Slot array antenna

A slot array antenna includes: first and second conductive members; and a ridge-shaped waveguide member on the second conductive member and conductive rods surrounding it. The waveguide member has a waveguide face which is opposed to a conductive surface of the first conductive member and which extends along a first direction. The first conductive member includes first and second slot groups each arranged along the first direction. The second conductive member has a throughhole which splits the waveguide member into first and second ridges. Some slots in the first and second slot groups are connected to a waveguide within the throughhole via a waveguide extending between the waveguide face of the first ridge and the conductive surface, and the remaining slots are connected to the waveguide within the throughhole via a waveguide extending between the waveguide face of the second ridge and the conductive surface.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 to Japanese Application No. 2018-113890 filed on Jun. 14, 2018, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a slot array antenna.

BACKGROUND

An array antenna (also referred to as an “antenna array”) which includes a plurality of radiating elements (also referred to as “antenna elements”) arrayed along a line or on a plane finds its use in various applications, e.g., radar and communication systems. In order to radiate electromagnetic waves from an array antenna, it is necessary to supply electromagnetic waves (e.g., radio-frequency signal waves) to each radiating element, from a circuit which generates electromagnetic waves. Such supply of signal waves is performed via a waveguide. A waveguide is also used to send electromagnetic waves that are received at the antenna elements to a reception circuit.

Conventionally, feed to an array antenna has often been achieved by using a microstrip line(s). However, in the case where the frequency of an electromagnetic wave to be transmitted or received by an array antenna is a high frequency above 30 gigahertz (GHz), as in the millimeter band, a microstrip line will incur a large dielectric loss, thus detracting from the efficiency of the antenna. Therefore, in such a radio frequency region, an alternative waveguide to replace a microstrip line is needed.

As alternative waveguide structures to the microstrip line and the hollow waveguide, the specification of U.S. Pat. No. 8,779,995, the specification of U.S. Pat. No. 8,803,638 and the specification of European Patent Application Publication No. 1331688, and Kirino et al., “A 76 GHz Multi-Layered Phased Array Antenna Using a Non-Metal Contact Metamaterial Waveguide”, IEEE Transaction on Antennas and Propagation, Vol. 60, No. 2, February 2012, pp 840-853, Kildal et al., “Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates”, IEEE Antennas and Wireless Propagation Letters, Vol. 8, 2009, pp. 84-87 and Syed Kamal Mustafa, Chalmers University of Technology, Master's Thesis “Hybrid Analog-Digital Beam-Steered Slot Antenna Array for mm-Wave Applications in Gap Waveguide Technology”, October 2015 disclose structures which guide electromagnetic waves by utilizing an artificial magnetic conductor (AMC) extending on both sides of a ridge-type waveguide. the specification of U.S. Pat. No. 8,779,995 and Kirino et al., “A 76 GHz Multi-Layered Phased Array Antenna Using a Non-Metal Contact Metamaterial Waveguide”, IEEE Transaction on Antennas and Propagation, Vol. 60, No. 2, February 2012, pp 840-853, Kildal et al., “Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates”, IEEE Antennas and Wireless Propagation Letters, Vol. 8, 2009, pp. 84-87 and Syed Kamal Mustafa, Chalmers University of Technology, Master's Thesis “Hybrid Analog-Digital Beam-Steered Slot Antenna Array for mm-Wave Applications in Gap Waveguide Technology”, October 2015, each disclose a slot array antenna utilizing such a waveguide structure.

On the other hand, Japanese Laid-Open Patent Publication No. 2005-167755 and the specification of U.S. Pat. No. 4,513,291 disclose a slot array antenna that includes a hollow waveguide having a plurality of slots.

The slot array antennas disclosed in Japanese Laid-Open Patent Publication No. 2005-167755 and the specification of U.S. Pat. No. 4,513,291 and Syed Kamal Mustafa, Chalmers University of Technology, Master's Thesis “Hybrid Analog-Digital Beam-Steered Slot Antenna Array for mm-Wave Applications in Gap Waveguide Technology”, October 2015 are able to radiate polarized waves whose electric field oscillates along a direction which is perpendicular to the direction that the waveguide extends. These slot array antennas include a plurality of rectangular slots as antenna elements, the rectangular slots being arrayed along the waveguide. Each of the plurality of slots is disposed so that its longitudinal direction coincides with the direction that the waveguide extends. Among the plurality of slots, any odd-numbered slot as counted from an end is located on one side of a center line of the waveguide, while any even-numbered slot is located on the other side of the center line of the waveguide. The interval between two adjacent slots along a direction that follows along the waveguide is approximately ½ of the wavelength of an electromagnetic wave propagating in the waveguide. With such a structure, even when the interval between slots along the direction following along the waveguide is shorter than the wavelength in the waveguide, the respective slots can be excited in the same phase.

SUMMARY

Example embodiments of the present disclosure provides techniques for providing slot array antennas each having good radiation characteristics, with a relatively simple construction.

A slot array antenna according to an example embodiment of the present disclosure includes a first electrically conductive member including a first electrically conductive surface on a front side and a second electrically conductive surface on a rear side, a second electrically conductive member including a third electrically conductive surface which is opposed to the second electrically conductive surface, a ridge-shaped waveguide member on the third electrically conductive surface, the waveguide member including an electrically-conductive waveguide surface which is opposed to the second electrically conductive surface and which extends along a first direction, and a plurality of electrically conductive rods disposed on both sides of the waveguide member, each including a root which is connected to the third electrically conductive surface and a leading end which is opposed to the second electrically conductive surface. The first electrically conductive member includes a plurality of slots. The plurality of slots includes a first slot group arranged along the first direction, and a second slot group being adjacent to the first slot group and arranged along the first direction. When viewed from a direction perpendicular to the waveguide surface, a center of each slot in the first slot group is located on one side of a center line of the waveguide surface, a center of each slot in the second slot group is located on another side of the center line of the waveguide surface, and a distance between the center of each slot in the first slot group and the second slot group and the center line of the waveguide surface is shorter than a distance between the center line of the waveguide surface and a center of an electrically conductive rod that is the closest to the center line. Along the first direction, a center of at least one slot in the first slot group is located between two adjacent slots in the second slot group. Along the first direction, the center of at least one slot in the second slot group is located between two adjacent slots in the first slot group. At least a central portion of an opening of each slot included in the first slot group and each slot included in the second slot group extends along the first direction, or along a direction that is inclined by an angle which is smaller than about 45 degrees from the first direction. The second electrically conductive member has a throughhole. The waveguide member is split by the throughhole into a first ridge and a second ridge. When viewed from a direction perpendicular to the waveguide surface, a center of the throughhole is located between one slot included in the first slot group and one slot included in the second slot group. A number of slots in the first slot group and the second slot group is or are connected to a waveguide within the throughhole via a first waveguide extending between the waveguide surface of the first ridge and the second electrically conductive surface. A remaining slot or slots in the first slot group and the second slot group is or are connected to the waveguide in the throughhole via a second waveguide extending between the waveguide surface of the second ridge and the second electrically conductive surface.

According to example embodiments of the present disclosure, slot array antennas having good radiation characteristics are realized with a relatively simple construction.

DETAILED DESCRIPTION

Prior to describing example embodiments of the present disclosure, findings that form the basis of the present disclosure will be described.

A ridge waveguide which is disclosed in the aforementioned specification of U.S. Pat. No. 8,779,995, the specification of U.S. Pat. No. 8,803,638 and the specification of European Patent Application Publication No. 1331688, and Kirino et al., “A 76 GHz Multi-Layered Phased Array Antenna Using a Non-Metal Contact Metamaterial Waveguide”, IEEE Transaction on Antennas and Propagation, Vol. 60, No. 2, February 2012, pp 840-853, Kildal et al., “Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates”, IEEE Antennas and Wireless Propagation Letters, Vol. 8, 2009, pp 84-87 and Syed Kamal Mustafa, Chalmers University of Technology, Master's Thesis “Hybrid Analog-Digital Beam-Steered Slot Antenna Array for mm-Wave Applications in Gap Waveguide Technology”, October 2015 is provided in a waffle iron structure which is capable of functioning as an artificial magnetic conductor. A ridge waveguide in which such an artificial magnetic conductor is utilized based on the present disclosure is able to realize an antenna feeding network with low losses in the microwave or the millimeter wave band. Moreover, use of such a ridge waveguide allows antenna elements to be disposed with a high density. Such a ridge waveguide may be referred to as a waffle-iron ridge waveguide (WRG) in the present specification. Hereinafter, an exemplary fundamental construction and operation of a waffle-iron ridge waveguide will be described.

An artificial magnetic conductor is a structure which artificially realizes the properties of a perfect magnetic conductor (PMC), which does not exist in nature. One property of a perfect magnetic conductor is that “a magnetic field on its surface has zero tangential component”. This property is the opposite of the property of a perfect electric conductor (PEC), i.e., “an electric field on its surface has zero tangential component”. Although no perfect magnetic conductor exists in nature, it can be embodied by an artificial structure, e.g., an array of a plurality of electrically conductive rods. An artificial magnetic conductor functions as a perfect magnetic conductor in a specific frequency band which is defined by its structure. An artificial magnetic conductor restrains or prevents an electromagnetic wave of any frequency that is contained in the specific frequency band (propagation-restricted band) from propagating along the surface of the artificial magnetic conductor. For this reason, the surface of an artificial magnetic conductor may be referred to as a high impedance surface.

In the waveguide devices disclosed in the specification of U.S. Pat. No. 8,779,995, the specification of U.S. Pat. No. 8,803,638 and the specification of European Patent Application Publication No. 1331688 and Kirino et al., “A 76 GHz Multi-Layered Phased Array Antenna Using a Non-Metal Contact Metamaterial Waveguide”, IEEE Transaction on Antennas and Propagation, Vol. 60, No. 2, February 2012, pp 840-853, Kildal et al., “Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates”, IEEE Antennas and Wireless Propagation Letters, Vol. 8, 2009, pp 84-87 and Syed Kamal Mustafa, Chalmers University of Technology, Master's Thesis “Hybrid Analog-Digital Beam-Steered Slot Antenna Array for mm-Wave Applications in Gap Waveguide Technology”, October 2015, an artificial magnetic conductor is realized by a plurality of electrically conductive rods which are arrayed along row and column directions. Such rods are projections which may also be referred to as posts or pins. Each of these waveguide devices includes, as a whole, a pair of opposing electrically conductive plates. One conductive plate has a ridge protruding toward the other conductive plate, and stretches of an artificial magnetic conductor extending on both sides of the ridge. An electrically-conductive upper face of the ridge is opposed to, via a gap, an electrically conductive surface of the other conductive plate. An electromagnetic wave (signal wave) of a wavelength which is contained in the propagation-restricted band of the artificial magnetic conductor propagates along the ridge, in the space (gap) between this conductive surface and the upper face of the ridge.

FIG. 1shows XYZ coordinates along X, Y and Z directions which are orthogonal to one another. The waveguide device100shown in the figure includes a plate-like (plate-shaped) first electrically conductive member110and a plate-like (plate-shaped) second electrically conductive member120, which are in opposing and parallel positions to each other. A plurality of electrically conductive rods124are arrayed on the second conductive member120.

Note that any structure appearing in a figure of the present application is shown in an orientation that is selected for ease of explanation, which in no way should limit its orientation when an example embodiment of the present disclosure is actually practiced. Moreover, the shape and size of a whole or a part of any structure that is shown in a figure should not limit its actual shape and size.

As shown inFIG. 2A, the first conductive member110has an electrically conductive surface110aon the side facing the second conductive member120. The conductive surface110ahas a two-dimensional expanse along a plane which is orthogonal to the axial direction (i.e., the Z direction) of the conductive rods124(i.e., a plane which is parallel to the XY plane). Although the conductive surface110ais shown to be a smooth plane in this example, the conductive surface110adoes not need to be a plane, as will be described later.

FIG. 3is a perspective view schematically showing the waveguide device100, illustrated so that the spacing between the first conductive member110and the second conductive member120is exaggerated for ease of understanding. In an actual waveguide device100, as shown inFIG. 1andFIG. 2A, the spacing between the first conductive member110and the second conductive member120is narrow, with the first conductive member110covering over all of the conductive rods124on the second conductive member120.

FIG. 1toFIG. 3only show portions of the waveguide device100. The conductive members110and120, the waveguide member122, and the plurality of conductive rods124actually extend to outside of the portions illustrated in the figures. At an end of the waveguide member122, as will be described later, a choke structure for preventing electromagnetic waves from leaking into the external space is provided. The choke structure may include a row of conductive rods that are adjacent to the end of the waveguide member122, for example.

SeeFIG. 2Aagain. The plurality of conductive rods124arrayed on the second conductive member120each have a leading end124aopposing the conductive surface110a. In the example shown in the figure, the leading ends124aof the plurality of conductive rods124are on the same plane. This plane defines the surface125of an artificial magnetic conductor. Each conductive rod124does not need to be entirely electrically conductive, so long as at least the surface (the upper face and the side faces) of the rod-like structure) is electrically conductive. Moreover, each second conductive member120does not need to be entirely electrically conductive, so long as it can support the plurality of conductive rods124to constitute an artificial magnetic conductor. Of the surfaces of the second conductive member120, a face carrying the plurality of conductive rods124may be electrically conductive, such that the electrical conductor electrically interconnects the surfaces of adjacent ones of the plurality of conductive rods124. In other words, the entire combination of the second conductive member120and the plurality of conductive rods124may at least include an electrically conductive surface with rises and falls opposing the conductive surface110aof the first conductive member110.

On the second conductive member120, a ridge-like waveguide member122is provided among the plurality of conductive rods124. More specifically, stretches of an artificial magnetic conductor are present on both sides of the waveguide member122, such that the waveguide member122is sandwiched between the stretches of artificial magnetic conductor on both sides. As can be seen fromFIG. 3, the waveguide member122in this example is supported on the second conductive member120, and extends linearly along the Y direction. In the example shown in the figure, the waveguide member122has the same height and width as those of the conductive rods124. As will be described later, however, the height and width of the waveguide member122may have respectively different values from those of the conductive rod124. Unlike the conductive rods124, the waveguide member122extends along a direction (which in this example is the Y direction) in which to guide electromagnetic waves along the conductive surface110a. Similarly, the waveguide member122does not need to be entirely electrically conductive, but may at least include an electrically conductive waveguide face122aopposing the conductive surface110aof the first conductive member110. The second conductive member120, the plurality of conductive rods124, and the waveguide member122may be portions of a continuous single-piece body. Furthermore, the first conductive member110may also be a portion of such a single-piece body.

On both sides of the waveguide member122, the space between the surface125of each stretch of artificial magnetic conductor and the conductive surface110aof the first conductive member110does not allow an electromagnetic wave of any frequency that is within a specific frequency band to propagate. This frequency band is called a “prohibited band”. The artificial magnetic conductor is designed so that the frequency of a signal wave to propagate in the waveguide device100(which may hereinafter be referred to as the “operating frequency”) is contained in the prohibited band. The prohibited band may be adjusted based on the following: the height of the conductive rods124, i.e., the depth of each groove formed between adjacent conductive rods124; the diameter of each conductive rod124; the interval between conductive rods124; and the size of the gap between the leading end124aand the conductive surface110aof each conductive rod124.

Next, with reference toFIG. 4, the dimensions, shape, positioning, and the like of each member in the structure shown inFIG. 2Awill be described. The waveguide device is used for at least one of transmission and reception of electromagnetic waves of a predetermined band (referred to as the “operating frequency band”). In the present specification, λo denotes a representative value of wavelengths in free space (e.g., a central wavelength corresponding to a center frequency in the operating frequency band) of an electromagnetic wave (signal wave) propagating in a waveguide extending between the conductive surface110aof the first conductive member110and the waveguide face122aof the waveguide member122. Moreover, λm denotes a wavelength, in free space, of an electromagnetic wave of the highest frequency in the operating frequency band. The end of each conductive rod124that is in contact with the second conductive member120is referred to as the “root”. As shown inFIG. 4, each conductive rod124has the leading end124aand the root124b. Examples of dimensions, shapes, positioning, and the like of the respective members are as follows.

(1) Width of the Conductive Rod

The width (i.e., the size along the X direction and the Y direction) of the conductive rod124may be set to less than λm/2. Within this range, resonance of the lowest order can be prevented from occurring along the X direction and the Y direction. Since resonance may possibly occur not only in the X and Y directions but also in any diagonal direction in an X-Y cross section, the diagonal length of an X-Y cross section of the conductive rod124is also preferably less than λm/2. The lower limit values for the rod width and diagonal length will conform to the minimum lengths that are producible under the given manufacturing method, but is not particularly limited.

(2) Distance from the Root of the Conductive Rod to the Conductive Surface of the First Conductive Member110

The distance from the root124bof each conductive rod124to the conductive surface110aof the first conductive member110may be longer than the height of the conductive rods124, while also being less than λm/2. When the distance is λm/2 or more, resonance may occur between the root124bof each conductive rod124and the conductive surface110a, thus reducing the effect of signal wave containment.

The distance from the root124bof each conductive rod124to the conductive surface110aof the first conductive member110corresponds to the spacing between the first conductive member110and the second conductive member120. For example, when a signal wave of 76.5±0.5 GHz (which belongs to the millimeter band or the extremely high frequency band) propagates in the waveguide, the wavelength of the signal wave is in the range from 3.8934 mm to 3.9446 mm. Therefore, λm equals 3.8934 mm in this case, so that the spacing between the first conductive member110and the second conductive member120may be set to less than a half of 3.8934 mm. So long as the first conductive member110and the second conductive member120realize such a narrow spacing while being disposed opposite from each other, the first conductive member110and the second conductive member120do not need to be strictly parallel. Moreover, when the spacing between the first conductive member110and the second conductive member120is less than λm/2, a whole or a part of the first conductive member110and/or the second conductive member120may be shaped as a curved surface. On the other hand, the conductive members110and120each have a planar shape (i.e., the shape of their region as perpendicularly projected onto the XY plane) and a planar size (i.e., the size of their region as perpendicularly projected onto the XY plane) which may be arbitrarily designed depending on the purpose.

Although the conductive surface120ais illustrated as a plane in the example shown inFIG. 2A, example embodiments of the present disclosure are not limited thereto. For example, as shown inFIG. 2B, the conductive surface120amay be the bottom parts of faces each of which has a cross section similar to a U-shape or a V-shape. The conductive surface120awill have such a structure when each conductive rod124or the waveguide member122is shaped with a width which increases toward the root. In this example, the waveguide member122and each the plurality of conductive rods124have slanted side faces at their root. The tilting angle of the waveguide member122and each conductive rod124at the top of their side faces is smaller than the tilting angle at their root. Even with such a structure, the device shown inFIG. 2Bcan function as the waveguide device according to an example embodiment of the present disclosure so long as the distance between the conductive surface110aand the conductive surface120ais less than a half of the wavelength λm.

(3) Distance L2from the Leading End of the Conductive Rod to the Conductive Surface

The distance L2from the leading end124aof each conductive rod124to the conductive surface110ais set to less than λm/2. When the distance is λm/2 or more, a propagation mode where electromagnetic waves reciprocate between the leading end124aof each conductive rod124and the conductive surface110amay occur, thus no longer being able to contain an electromagnetic wave. Note that, among the plurality of conductive rods124, at least those which are adjacent to the waveguide member122do not have their leading ends in electrical contact with the conductive surface110a. As used herein, the leading end of a conductive rod not being in electrical contact with the conductive surface means either of the following states: there being an air gap between the leading end and the conductive surface; or the leading end of the conductive rod and the conductive surface adjoining each other via an insulating layer which may exist in the leading end of the conductive rod or in the conductive surface.

(4) Arrangement and Shape of Conductive Rods

The interspace between two adjacent conductive rods124among the plurality of conductive rods124has a width of less than λm/2, for example. The width of the interspace between any two adjacent conductive rods124is defined by the shortest distance from the surface (side face) of one of the two conductive rods124to the surface (side face) of the other. This width of the interspace between rods is to be determined so that resonance of the lowest order will not occur in the regions between rods. The conditions under which resonance will occur are determined based by a combination of: the height of the conductive rods124; the distance between any two adjacent conductive rods; and the capacitance of the air gap between the leading end124aof each conductive rod124and the conductive surface110a. Therefore, the width of the interspace between rods may be appropriately determined depending on other design parameters. Although there is no clear lower limit to the width of the interspace between rods, for manufacturing ease, it may be e.g. λm/16 or more when an electromagnetic wave in the extremely high frequency range is to be propagated. Note that the interspace does not need to have a constant width. So long as it remains less than λm/2, the interspace between conductive rods124may vary.

The arrangement of the plurality of conductive rods124is not limited to the illustrated example, so long as it exhibits a function of an artificial magnetic conductor. The plurality of conductive rods124do not need to be arranged in orthogonal rows and columns; the rows and columns may be intersecting at angles other than 90 degrees. The plurality of conductive rods124do not need to form a linear array along rows or columns, but may be in a dispersed arrangement which does not present any straight-forward regularity. The conductive rods124may also vary in shape and size depending on the position on the second conductive member120.

The surface125of the artificial magnetic conductor that are constituted by the leading ends124aof the plurality of conductive rods124does not need to be a strict plane, but may be a plane with minute rises and falls, or even a curved surface. In other words, the conductive rods124do not need to be of uniform height, but rather the conductive rods124may be diverse so long as the array of conductive rods124is able to function as an artificial magnetic conductor.

Each conductive rod124does not need to have a prismatic shape as shown in the figure, but may have a cylindrical shape, for example. Furthermore, each conductive rod124does not need to have a simple columnar shape. The artificial magnetic conductor may also be realized by any structure other than an array of conductive rods124, and various artificial magnetic conductors are applicable to the waveguide device of the present disclosure. Note that, when the leading end124aof each conductive rod124has a prismatic shape, its diagonal length is preferably less than λm/2. When the leading end124aof each conductive rod124is shaped as an ellipse, the length of its major axis is preferably less than λm/2. Even when the leading end124ahas any other shape, the dimension across it is preferably less than λm/2 even at the longest position.

The height of each conductive rod124(in particular, those conductive rods124which are adjacent to the waveguide member122), i.e., the length from the root124bto the leading end124a, may be set to a value which is shorter than the distance (i.e., less than λm/2) between the conductive surface110aand the conductive surface120a, e.g., λo/4.

(5) Width of the Waveguide Face

The width of the waveguide face122aof the waveguide member122, i.e., the size of the waveguide face122aalong a direction which is orthogonal to the direction that the waveguide member122extends, may be set to less than λm/2 (e.g. λo/8). If the width of the waveguide face122ais λm/2 or more, resonance will occur along the width direction, which will prevent any WRG from operating as a simple transmission line.

(6) Height of the Waveguide Member

The height (i.e., the size along the Z direction in the example shown in the figure) of the waveguide member122is set to less than λm/2. The reason is that, if the distance is λm/2 or more, the distance between the root124bof each conductive rod124and the conductive surface110awill be λm/2 or more. Similarly, the height of each conductive rod124(in particular, those conductive rods124which are adjacent to the waveguide member122) is also set to less than λm/2.

(7) Distance L1Between the Waveguide Face and the Conductive Surface

The distance L1between the waveguide face122aof the waveguide member122and the conductive surface110ais set to less than λm/2. If the distance is λm/2 or more, resonance will occur between the waveguide face122aand the conductive surface110a, which will prevent functionality as a waveguide. In one example, the distance is λm/4 or less. In order to ensure manufacturing ease, when an electromagnetic wave in the extremely high frequency range is to propagate, the distance is preferably λm/16 or more, for example.

The lower limit of the distance L1between the conductive surface110aand the waveguide face122aand the lower limit of the distance L2between the conductive surface110aand the leading end124aof each conductive rod124depends on the machining precision, and also on the precision when assembling the two up-per/lower conductive members110and120so as to be apart by a constant distance. When a pressing technique or an injection technique is used, the practical lower limit of the aforementioned distance is about 50 micrometers (μm). In the case of using an MEMS (Micro-Electro-Mechanical System) to make a product in e.g. the terahertz range, the lower limit of the aforementioned distance is about 2 to about 3 μm.

Next, variants of waveguide structures including the waveguide member122, the conductive members110and120, and the plurality of conductive rods124will be described. The following variants are applicable to the WRG structure in any place in each example embodiment described below.

FIG. 5Ais a cross-sectional view showing an exemplary structure in which only the waveguide face122a, defining an upper face of the waveguide member122, is electrically conductive, while any portion of the waveguide member122other than the waveguide face122ais not electrically conductive. Both of the conductive member110and the conductive member120alike are only electrically conductive at their surface that has the waveguide member122provided thereon (i.e., the conductive surface110a,120a), while not being electrically conductive in any other portions. Thus, each of the waveguide member122, the conductive member110, and the conductive member120does not need to be electrically conductive.

FIG. 5Bis a diagram showing a variant in which the waveguide member122is not formed on the conductive member120. In this example, the waveguide member122is fixed to a supporting member (e.g., the inner wall of the housing) that supports the conductive members110and120. A gap exists between the waveguide member122and the conductive member120. Thus, the waveguide member122does not need to be connected to the conductive member120.

FIG. 5Cis a diagram showing an exemplary structure where the conductive member120, the waveguide member122, and each of the plurality of conductive rods124are composed of a dielectric surface that is coated with an electrically conductive material such as a metal. The conductive member120, the waveguide member122, and the plurality of conductive rods124are connected to one another via the electrical conductor. On the other hand, the conductive member110is made of an electrically conductive material such as a metal.

FIG. 5DandFIG. 5Eare diagrams each showing an exemplary structure in which dielectric layers110cand120care respectively provided on the outermost surfaces of conductive members110and120, a waveguide member122, and conductive rods124.FIG. 5Dshows an exemplary structure in which the surface of metal conductive members, which are electrical conductors, are covered with a dielectric layer.FIG. 5Eshows an example where the conductive member120is structured so that the surface of members which are composed of a dielectric, e.g., resin, is covered with an electrical conductor such as a metal, this metal layer being further coated with a dielectric layer. The dielectric layer that covers the metal surface may be a coating of resin or the like, or an oxide film of passivation coating or the like which is generated as the metal becomes oxidized.

The dielectric layer on the outermost surface will allow losses to be increased in the electromagnetic wave propagating through the WRG waveguide, but is able to protect the conductive surfaces110aand120a(which are electrically conductive) from corrosion. It also prevents influences of a DC voltage, or an AC voltage of such a low frequency that it is not capable of propagation on certain WRG waveguides.

FIG. 5Fis a diagram showing an example where the height of the waveguide member122is lower than the height of the conductive rods124, and the portion of the conductive surface110aof the conductive member110that is opposed to the waveguide face122aprotrudes toward the waveguide member122. Even such a structure will operate in a similar manner to the above-described construction, so long as the ranges of dimensions depicted inFIG. 4are satisfied.

FIG. 5Gis a diagram showing an example where, further in the structure ofFIG. 5F, portions of the conductive surface110athat oppose the conductive rods124protrude toward the conductive rods124. Even such a structure will operate in a similar manner to the above-described example, so long as the ranges of dimensions depicted inFIG. 4are satisfied. Instead of a structure in which the conductive surface110apartially protrudes, a structure in which the conductive surface110ais partially dented may be adopted.

FIG. 6Ais a diagram showing an example where a conductive surface110aof the conductive member110is shaped as a curved surface.FIG. 6Bis a diagram showing an example where also a conductive surface120aof the conductive member120is shaped as a curved surface. As demonstrated by these examples, the conductive surfaces110aand120amay not be shaped as planes, but may be shaped as curved surfaces. A conductive member having a conductive surface which is a curved surface is also qualifies as a conductive member having a “plate shape”.

In the waveguide device100of the above-described construction, a signal wave of the operating frequency is unable to propagate in the space between the surface125of the artificial magnetic conductor and the conductive surface110aof the conductive member110, but propagates in the space between the waveguide face122aof the waveguide member122and the conductive surface110aof the conductive member110. Unlike in a hollow waveguide, the width of the waveguide member122in such a waveguide structure does not need to be equal to or greater than a half of the wavelength of the electromagnetic wave to propagate. Moreover, the conductive member110and the conductive member120do not need to be electrically interconnected by a metal wall that extends along the thickness direction (i.e., in parallel to the YZ plane).

FIG. 7Aschematically shows an electromagnetic wave that propagates in a narrow space, i.e., a gap between the waveguide face122aof the waveguide member122and the conductive surface110aof the conductive member110. Three arrows inFIG. 7Aschematically indicate the orientation of an electric field of the propagating electromagnetic wave. The electric field of the propagating electromagnetic wave is perpendicular to the conductive surface110aof the conductive member110and to the waveguide face122a.

On both sides of the waveguide member122, stretches of artificial magnetic conductor that are created by the plurality of conductive rods124are present. An electromagnetic wave propagates in the gap between the waveguide face122aof the waveguide member122and the conductive surface110aof the conductive member110.FIG. 7Ais schematic, and does not accurately represent the magnitude of an electromagnetic field to be actually created by the electromagnetic wave. A part of the electromagnetic wave (electromagnetic field) propagating in the space over the waveguide face122amay have a lateral expanse, to the outside (i.e., toward where the artificial magnetic conductor exists) of the space that is delineated by the width of the waveguide face122a. In this example, the electromagnetic wave propagates in a direction (i.e., the Y direction) which is perpendicular to the plane ofFIG. 7A. As such, the waveguide member122does not need to extend linearly along the Y direction, but may include a bend(s) and/or a branching portion(s) not shown. Since the electromagnetic wave propagates along the waveguide face122aof the waveguide member122, the direction of propagation would change at a bend, whereas the direction of propagation would ramify into plural directions at a branching portion.

In the waveguide structure ofFIG. 7A, no metal wall (electric wall), which would be indispensable to a hollow waveguide, exists on both sides of the propagating electromagnetic wave. Therefore, in the waveguide structure of this example, “a constraint due to a metal wall (electric wall)” is not included in the boundary conditions for the electromagnetic field mode to be created by the propagating electromagnetic wave, and the width (size along the X direction) of the waveguide face122ais less than a half of the wavelength of the electromagnetic wave.

For reference,FIG. 7Bschematically shows a cross section of a hollow waveguide330. With arrows,FIG. 7Bschematically shows the orientation of an electric field of an electromagnetic field mode (TE10) that is created in the internal space332of the hollow waveguide330. The lengths of the arrows correspond to electric field intensities. The width of the internal space332of the hollow waveguide330needs to be set to be broader than a half of the wavelength. In other words, the width of the internal space332of the hollow waveguide330cannot be set to be smaller than a half of the wavelength of the propagating electromagnetic wave.

FIG. 7Cis a cross-sectional view showing an implementation where two waveguide members122are provided on the conductive member120. Thus, an artificial magnetic conductor that is created by the plurality of conductive rods124exists between the two adjacent waveguide members122. More accurately, stretches of artificial magnetic conductor created by the plurality of conductive rods124are present on both sides of each waveguide member122, such that each waveguide member122is able to independently propagate an electromagnetic wave.

For reference's sake,FIG. 7Dschematically shows a cross section of a waveguide device in which two hollow waveguides330are placed side-by-side. The two hollow waveguides330are electrically insulated from each other. Each space in which an electromagnetic wave is to propagate needs to be surrounded by a metal wall that defines the respective hollow waveguide330. Therefore, the interval between the internal spaces332in which electromagnetic waves are to propagate cannot be made smaller than a total of the thicknesses of two metal walls. Usually, a total of the thicknesses of two metal walls is longer than a half of the wavelength of a propagating electromagnetic wave. Therefore, it is difficult for the interval between the hollow waveguides330(i.e., interval between their centers) to be shorter than the wavelength of a propagating electromagnetic wave. Particularly for electromagnetic waves of wavelengths in the extremely high frequency range (i.e., electromagnetic wave wavelength: 10 mm or less) or even shorter wavelengths, a metal wall which is sufficiently thin relative to the wavelength is difficult to be formed. This presents a cost problem in commercially practical implementation.

On the other hand, a waveguide device100including an artificial magnetic conductor can easily realize a structure in which waveguide members122are placed close to one another. Thus, such a waveguide device100can be suitably used in an array antenna that includes plural antenna elements in a close arrangement.

Next, an exemplary construction for a slot antenna utilizing the aforementioned waveguide structure will be described. A “slot antenna” means an antenna device having one or plural slots (also referred to as “throughholes”) as antenna elements. In particular, a slot antenna having a plurality of slots as antenna elements will be referred to as a “slot array antenna” or a “slot antenna array”.

FIG. 8Ais a perspective view showing an exemplary slot antenna200which is capable of radiating an example of a polarized wave whose electric field oscillates along the X direction.FIG. 8Bis a diagram schematically showing a partial cross section which passes through the center of a slot112of the slot antenna200shown inFIG. 8A, the cross section being taken parallel to the XZ plane. The slot112of the slot antenna200is shaped so that its length direction coincides with the Y direction, and the position of its center along the X direction differs from the position of the center of the waveguide member122along the X direction. For simplicity, a construction in the case where the first conductive member110has one slot112will be described. As will be described later, a slot array antenna can be realized by providing two or more slots112.

The slot antenna200includes a first conductive member110, a second conductive member120, a waveguide member122, and an artificial magnetic conductor (which in this example includes a plurality of conductive rods124). The first conductive member110has a first conductive surface110awhich is shaped as a plane or a curved surface. The first conductive member110has the slot112. The second conductive member120has a second conductive surface120aopposing the first conductive surface110a. The waveguide member122has a stripe-shaped electrically-conductive waveguide face122aopposing the first conductive surface110aof the first conductive member110. In the present specification, a “stripe shape” means a shape which is defined by a single stripe, rather than a shape constituted by stripes. Not only shapes that extend linearly in one direction, but also any shape that bends or branches along the way is also encompassed by a “stripe shape”. A “stripe shape” may also be referred to as a “strip shape”.

Between the first conductive member110and the second conductive member120, the artificial magnetic conductor is at least disposed on both sides of the waveguide member122. Adjacent to the waveguide member122, plural conductive rods124functioning as the artificial magnetic conductor are disposed on both side of the waveguide member122.

The slot antenna200is used for at least one of transmission and reception of electromagnetic waves of a predetermined band. Assuming that, among the electromagnetic waves of the predetermined band, an electromagnetic wave of the highest frequency has a wavelength λm in free space, the width of the waveguide member122, the width of each conductive rod124, the width of a space between two adjacent conductive rods124, the distance between the first conductive surface110aand the second conductive surface120a, and the width of a space between any conductive rod124that is adjacent to the waveguide member122and the waveguide member122are all less than λm/2.

The slot112, which is a throughhole made in the first conductive member110, is a region that is surrounded by an electrically-conductive inner wall surface of the first conductive member110. As shown inFIG. 8B, the slot112has an opening112athat extends through the first conductive member110and is open on the first conductive surface110a. The opening112arefers to a portion of the slot112that can be regarded as coplanar with the first conductive surface110a. The opening112aof the slot112has: a length that is defined by a straight line (line segment) or a curve (including a combination of line segments); and a width, i.e., a dimension along a perpendicular direction to the length direction. Note that a straight line or curve that defines the length of the opening112ais an imaginary straight line or curve connecting between central points on the width of the opening from one end to the other end of the opening, rather than any line or curve that constitutes a part of an edge of the opening112a. In the case of an I-shaped slot112that extends like a line as illustrated in the figure, the length of the opening is equal to the length of that line. As will be described later, the slot112may also have a shape other than an I shape.

In the example ofFIG. 8A, the length of the slot112along the Y direction is set to a value which is greater than a half of the central wavelength λo of the signal wave in free space. When this condition is met, an electromagnetic wave of the wavelength λo is able to pass through the slot112. Having such a slot112, the slot antenna200is able to transmit or receive an electromagnetic wave whose electric field oscillates along a direction (the X direction) which is perpendicular to the direction that the waveguide member122extends (the Y direction).

FIG. 8Cis an upper plan view showing a relative positioning between the slot112, the waveguide member122, and the plurality of conductive rods124.FIG. 8Cillustrates the slot112as viewed from the normal direction of the conductive surface110aof the first conductive member110. InFIG. 8C, the waveguide member122and the plurality of conductive rods124that are on the rear side (i.e., the −Z direction side) of the first conductive member110are depicted by dotted lines. The waveguide face122aof the waveguide member122has two edges122b1and122b2defining the width of the waveguide face122a. In this example, when viewed from the normal direction of the first conductive surface110a, the width direction of the opening of the slot112coincides with the width direction of the waveguide face122a(i.e., both being the X direction). On the outside of one edge122b1of the waveguide face122a(which corresponds to the left-hand side inFIG. 8C), the entire opening of the slot112is opposed to the second conductive surface120aof the second conductive member120. When viewed from the normal direction of the first conductive surface110a, the opening of the slot112just lies close to the one edge122b1, without intersecting either of the two edges122b1and122b2of the waveguide face122a.

The slot antenna200is connected to an electronic circuit not shown (e.g., a millimeter wave integrated circuit). During transmission, an electromagnetic wave (signal wave) is supplied from this electronic circuit to the waveguide extending between the waveguide face122aof the waveguide member122and the conductive surface110aof the first conductive member110.

FIG. 8Dis a diagram schematically showing an example of an electric field which may be created inside the slot112at a moment during transmission or during reception. Arrows in the figure illustrate the orientation of the electric field, while the length of each arrow corresponds to the intensity of the electric field. The slot112has an I shape which is longer along the Y direction than along the X direction, such that the position of the center of the slot112along the X direction is located in the −X direction from the position of the center of the waveguide face122a. The oscillation direction of the electric field that is created inside the slot112is perpendicular to the inner wall surface of the slot112, and has an increasing amplitude toward the center. Therefore, near the center of the slot112, an electric field exists that oscillates along the width direction (the X direction) of the waveguide face122a. In other words, an electromagnetic wave having a strong field component along the X direction can be transmitted or received. Assuming that the X direction is the horizontal direction and that the Y direction is the vertical direction, a polarized wave in the horizontal direction can be transmitted or received.

In this example, the entire opening of the slot112is opposed to the second conductive surface120a. Without being limited to such construction, only a portion of the opening of the slot112may be opposed to the second conductive surface120a.

FIG. 9Ais an upper plan view showing an example where only a portion of the slot112is opposed to the second conductive surface120a. In this construction, the slot112is located more in the +X direction than inFIG. 8C. As a result, a portion of the slot112is opposed to the second conductive surface120a, while another portion of the slot112is opposed to the waveguide face122a. With such an arrangement of the slot112, too, an electromagnetic wave whose electric field oscillates along the X direction can be transmitted or received.

FIG. 9Bis an upper plan view showing another example where only a portion of the slot112is opposed to the second conductive surface120a. In this example, in plan view, the length direction of the slot112intersects the direction that the waveguide face122aextends (i.e., the Y direction). The angle that is created between the length direction of the slot112and the direction that the waveguide face122aextends is smaller than 45 degrees. When viewed from the normal direction of the conductive surface110a,120a, the slot112has a portion overlapping the second conductive surface120a, a portion overlapping the waveguide face122a, and a portion overlapping the conductive rod124. The main direction of an electric field of an electromagnetic wave to be transmitted or received is not the X direction itself but a direction that intersects the width direction (the X direction) of the waveguide face122aat an angle which is smaller than 45 degrees. However, even in this case, it is possible to transmit or receive an electromagnetic wave having a stronger field component along the width direction of the waveguide face122a(the X direction) than along the direction that the waveguide face122aextends (the Y direction).

Thus, when viewed from the normal direction of the first conductive surface110a, the length direction of the slot112intersects the direction that the waveguide face122aextends at an angle which is smaller than 45 degrees, and the center of the opening of the slot112is located in the X direction of the center line of the waveguide face122a. Such construction enables at least one of transmission and reception of an electromagnetic wave having a greater field component along the X direction than along the Y direction.

Although the above example illustrates that the slot112is I-shaped, the slot112may have any other shape. According to example embodiments of the present disclosure, the shape and arrangement of the slot may be arbitrary so long as the following requirements (1) to (3) are satisfied.

(1) When viewed from the normal direction of the first conductive surface110a, at least in the central portion of the length direction of the opening, the opening of the slot112includes a portion in which the angle made between the width direction of the opening and the width direction of the waveguide face122ais smaller than 45 degrees (referred to as a “small-angle portion”).

(2) When viewed from the normal direction of the first conductive surface110a, at least a portion of the small-angle portion overlaps the second conductive surface120aon the outside of one (122b1) of the two edges of the waveguide face122a.

(3) When viewed from the normal direction of the first conductive surface110a, the small-angle portion intersects the one122b1of the two edges of the waveguide face122abut does not intersect the other122b2of the two edges, or is located, at a shorter distance than the width of the waveguide face122a, from the one122b1of the two edges.

FIGS. 10A through 10Eshow some example shapes for the opening of the slot112that may be used in the slot antenna200. In each of these figures, a double-headed arrow represents the length direction of the opening of the slot112. The length of the double-headed arrow indicates the length of the opening of the slot112. The opening of the slot112in each example has: a length that is defined by a straight line (line segment) or a curve (including a combination of line segments); and a width, i.e., a dimension along a perpendicular direction to the length direction. In the following description, the opening of the slot112may simply be referred to as the slot112. In any of these examples, the length of the slot112is set to a value such that higher-order resonance will not occur and that the slot impedance will not be too small. Typically, the length of the slot112is set to a value which is greater than λo/2 and less than λo, where λo is a wavelength in free space of an electromagnetic wave at the center frequency of the operating frequency band of the slot antenna200.

FIG. 10Ashows an exemplary of an I-shaped slot112that has been described above. In the I-shaped slot112, a length is defined by a line segment interconnecting both ends of the slot112. The width direction remains the same wherever along the length direction. Both ends of the slot112may be rounded or flat. An I-shaped slot of a shape similar to an ellipse, or a rectangular shape, may also be used. In the case of adopting an I-shaped slot112, it is to be disposed so that the entire opening of the slot112corresponds to the “small-angle portion”. That is, the I-shaped slot112is disposed so that the angle between the width direction and the width direction of the waveguide face122ais smaller than 45 degrees across the entire opening.

FIG. 10Bshows an exemplary slot112whose length is defined along a U-shaped curve (which in this example is a combination of three line segments). The slot112of this example includes a pair of parallel linear portions and another linear portion connecting the ends thereof. A shape that results by rotating the slot112shown inFIG. 10Bclockwise by 90 degrees would resemble the alphabetical letter “U”. Therefore, such a slot112may be referred to as a “U-shaped slot” in the present specification. In the case of adopting a U-shaped slot, it is to be disposed so that a bottom corresponding to the central portion (i.e., the right linear portion inFIG. 10B) corresponds to the “small-angle portion”.

FIG. 10Cshows an exemplary slot112whose length is defined along an inverted Z-shaped curve (which in this example is a combination of three line segments). A slot that results by inverting the slot shown inFIG. 10Cfrom right to left, whose length is defined along a Z-shaped curve, may be used. Such a slot112may be referred to as a “Z-shaped slot” in the present specification. A Z-shaped slot also includes a pair of parallel linear portions and another linear portion connecting the ends thereof. In the case of adopting a Z-shaped slot, it is to be disposed so that its middle linear portion corresponds to the “small-angle portion”.

FIG. 10Dshows an exemplary slot112having a shape resembling the alphabetical letter “H”. Such a slot112includes a pair of parallel linear portions and another linear portion interconnecting the central portions of the pair of linear portions. Such a slot112may be referred to as an “H-shaped slot”. The length of an H-shaped slot112is defined as a sum of: a half of a sum of the lengths of the pair of parallel linear portions; and the distance between the centers of the pair of linear portions. In the case of adopting an H-shaped slot, it is to be disposed so that its middle linear portion corresponds to the “small-angle portion”.

FIG. 10Eshows an exemplary slot112whose length is defined by an arc-shaped curve. Alternatively, a slot whose length is defined by any curve other than an arc shape may also be used. Such a slot112may be referred to as a “curve-shaped slot”. In any curve-shaped slot that does not include a linear portion, its width direction will continuously change from position to position along the length direction. In the case of adopting a curve-shaped slot112, too, it is to be disposed so that the angle made between the width direction in its central portion and the width direction of the waveguide face122ais smaller than 45 degrees.

Next, with reference toFIGS. 11A through 11E, several examples of relative positioning between the slot112and the waveguide face122awill be described. InFIGS. 11A through 11E, the small-angle portion of the opening of the slot112is shown hatched. All ofFIGS. 11A through 11Eare diagrams viewed from the normal direction of the first conductive surface110a. For ease of viewing, elements other than the slot112and the waveguide face122aare omitted from illustration.

FIG. 11Ashows an example where the slot112is U-shaped and a portion of the opening of the slot112is opposed to the waveguide face122a. When viewed from the normal direction of the first conductive surface110a(which is identical to the normal direction of the waveguide face122a), the small-angle portion112sin the slot112of this example intersects one of the two edges of the waveguide face122abut does not intersect the other edge. A portion of the small-angle portion112sis opposed to the waveguide face122a, while another portion is opposed to the second conductive surface120a. In this example, a polarized wave whose electric field oscillates along a direction that is inclined by an angle from the width direction of the waveguide face122a, the angle being smaller than 45 degrees, is transmitted or received.

FIG. 11Bshows an example where the slot112is U-shaped and the entire opening of the slot112is not opposed to the waveguide face122a. When viewed from the normal direction of the first conductive surface110a, the small-angle portion112sin the slot112of this example intersects neither of the two edges of the waveguide face122a, but abuts with one of the two edges. The entire small-angle portion112sis opposed to the second conductive surface120a. Since the width direction of the small-angle portion112scoincides with the width direction of the waveguide face122a, a polarized wave whose electric field oscillates along this direction is transmitted or received.

FIG. 11Cshows an example where the slot112is a curve-shaped (or crescent-shaped) slot, such that a portion of the opening of the slot112is opposed to the waveguide face122a. When viewed from the normal direction of the first conductive surface110a, the small-angle portion112sof the slot112of this example intersects one of the two edges of the waveguide face122abut does not intersect the other. A portion of the small-angle portion112sis opposed to the waveguide face122a, while another portion is opposed to the second conductive surface120a. In this example, near the central portion of the slot112, an electromagnetic wave whose electric field oscillates along a direction which approximates the width direction of the waveguide face122ais transmitted or received.

FIG. 11Dshows an example where the slot112is Z-shaped slot and only an end of the opening of the slot112is opposed to the waveguide face122a. When viewed from the normal direction of the first conductive surface110a, the small-angle portion112soverlaps the second conductive surface120aon the outside of one of the two edges of the waveguide face122a. The small-angle portion112sis located, at a shorter distance D than the width W of the waveguide face122a, from the one of the two edges. Thus, in plan view, the small-angle portion112smay be distant from the waveguide face122a. If it is too distant, however, an electromagnetic field of sufficient intensity will not be created in the slot112. Therefore, in the example ofFIG. 11D, the distance D between the small-angle portion112sand the closer edge of the waveguide face122ain plan view is made shorter than the width W of the waveguide face122a. This condition being satisfied can prevent the intensity of the electromagnetic field within the slot112from becoming too small. In the present specification, the distance D between the small-angle portion112sand one of the edges of the waveguide face122ais meant to be a distance from that edge to a place within the region of the small-angle portion112sthat is shortest in distance to that edge. In the case of adopting the slot112ofFIG. 11D, near the central portion of the small-angle portion112s, a polarized wave whose electric field oscillates along a direction that intersects the width direction of the waveguide face122aat an angle which is smaller than 45 degrees is transmitted or received.

FIG. 11Eshows an example where the slot112is an H-shaped slot, such that the opening of the slot112is disposed astride two edges of the waveguide face122a. When viewed from the normal direction of the first conductive surface110a, the small-angle portion112sintersects one of the two edges of the waveguide face122abut does not intersect the other. However, portions of the opening of the slot112except for the small-angle portion112s(two ends) each intersect both of the two edges of the waveguide face122a. With such construction, too, at the central portion of the slot112, a polarized wave whose electric field oscillates along the width direction of the waveguide face122acan be transmitted or received.

As described above, the shape and arrangement of the slot112to be adopted in example embodiments of the present disclosure may be various. Satisfying the above requirements (1) to (3) enables at least one of transmission and reception of a polarized wave whose electric field oscillates along the width direction of the waveguide face122aor a direction that intersects this direction at an angle which is smaller than 45 degrees.

Next, an exemplary construction of a slot antenna (slot array antenna) having a plurality of slots will be described.

FIG. 12is a perspective view schematically showing an exemplary construction for a slot array antenna200A having a plurality of slots112which are disposed alongside the waveguide face122a.FIG. 13is an upper plan view showing relative positioning between the plurality of slots112, the waveguide face122a, and the plurality of conductive rods124in this example. In this example, the first conductive member110has a plurality of slots112that are located along one122b1of the two edges of the waveguide face122aand a plurality of slots112that are located along the other122b2of the two edges. In the following description, the former plurality of slots may be referred to as “first type of slots”, and as an aggregation they may be referred to as the “first slot group”. The latter plurality of slots may be referred to as the second type of slots”, and as an aggregation they may be referred to as the “second slot group”. Each of the plurality of slots112has an I shape. The length direction of each slot112coincides with the direction that the waveguide member122extends (i.e., the Y direction). The entire opening of each slot112is opposed to the second conductive surface120a, but is not opposed to the waveguide face122aand the leading ends of the plurality of conductive rods124. Stated otherwise, when viewed from the normal direction of the first conductive surface110a, the opening of each slot112does not overlap the waveguide member122and the artificial magnetic conductor.

In this example, a plurality of first type of slots and a plurality of second type of slots alternate. In other words, regarding a direction following along the waveguide face122a(i.e., the Y direction), any second type of slot is located between two first type of slots adjacent to each other along the Y direction, among the plurality of first type of slots. Similarly, regarding the Y direction, any first type of slots is located between two second type of slots adjacent to each other along the Y direction, among the plurality of second type of slots. Such an arrangement for the slots112may be called a “staggered arrangement”.

The interval between the centers of two adjacent ones of the plurality of slots112along the Y direction is set to λg/2. Herein, λg is a wavelength of an electromagnetic wave (having a free space wavelength of λo) at the center frequency in the operating frequency band of the slot array antenna200A when propagating in the waveguide extending between the waveguide face122aand the first conductive surface110a. By ensuring that the interval between the centers of two adjacent slots112along the Y direction is λg/2, during signal wave transmission, the phase of the signal wave can be shifted by a half wavelength (180 degrees or n) at the positions of the two adjacent slots112. As a result, electromagnetic waves whose electric field oscillates along the same direction can be radiated from the plurality of slots112. In other words, electromagnetic waves with an equal phase can be radiated from the plurality of slots112.

Note that the interval, as taken along the Y direction, between the centers of two adjacent slots112along the direction following along the waveguide member122(i.e., the Y direction) does not need to be λg/2. Similar effects can be obtained so long as: the distance between any two closest first type of slots and the distance between any two closest second type of slots regarding the Y direction are an integer multiple of λg; and the distance between any closest ones of the first type of slots and the second type of slots regarding the Y direction is a half-integer multiple of λg. Depending on the purpose, the above conditions regarding distance do not need to be strictly satisfied. For example, regarding the Y direction, the distance between any two closest first type of slots and the distance between any two closest second type of slots may be an integer multiple of a given distance a (where a is equal to or greater than 0.5λo and smaller than 1.5λo), and the distance between any closest ones of the first type of slots and the second type of slots along the Y direction may be a half-integer multiple of the distance a.

Based on such construction, an array antenna can be realized such that an electromagnetic wave which has an equal phase and whose electric field oscillates along the width direction of the waveguide face122ais transmitted from each of the plurality of slots112. Therefore, assuming that the X direction is the horizontal direction and that the Y direction is the vertical direction, for example, a high-gain array antenna can be realized that is capable of transmitting or receiving a polarized wave whose electric field oscillates along the horizontal direction.

The aforementioned shape, arrangement, and number of slots112are only examples; various modifications thereof may be possible. Hereinafter, some variants will be illustrated.

FIG. 14Ashows an example where a portion of each slot112is opposed to the waveguide face122a. With such an arrangement, too, a polarized wave whose electric field oscillates along the X direction can be transmitted or received.

FIG. 14Bshows an example where the length direction of each slot112is inclined by an angle which is smaller than 45 degrees from the direction that the waveguide face122aextends (the Y direction). With such an arrangement, a polarized wave whose electric field oscillates along a direction that is inclined from the X direction can be transmitted or received.

Although the above example illustrates that the shape of each slot112is an I shape, each slot112may alternatively have another shape. Among the plurality of slots112, the first type of slots being located along one edge122b1of the waveguide face122amay satisfy the aforementioned requirements (1) to (3). On the other hand, the second type of slots being located along the other edge122b2of the waveguide face122amay satisfy the following requirements (1′) to (3′).

(1′) When viewed from the normal direction of the first conductive surface110a, at least in the central portion of the length direction of the opening, the opening of the slot112includes a portion in which the angle made between the width direction of the opening and the width direction of the waveguide face122ais smaller than 45 degrees (small-angle portion).

(2′) When viewed from the normal direction of the first conductive surface110a, at least a portion of the small-angle portion overlaps the second conductive surface120aon the outside of the other (122b2) of the two edges of the waveguide face122a(corresponding to the right-hand side ofFIG. 14).

(3′) When viewed from the normal direction of the first conductive surface110a, the small-angle portion intersects the other122b2of the two edges of the waveguide face122abut does not intersect the one122b1of the two edges, or is located, at a shorter distance than the width of the waveguide face122a, from the other122b2of the two edges.

While being substantially identical to the requirements (1) to (3), the requirements (1′) to (3′) define a distinct relative positioning between the slots112and the two edges of the waveguide face122a.

Hereinafter, some other examples of the shape and arrangement of the slot112will be illustrated.

FIG. 15Ashows an example where each slot112is U-shaped.FIG. 15Bshows an example where each slot112is Z-shaped.FIG. 15Cshows an example where each slot112is H-shaped.FIG. 15Dshows an example where each slot112is curve-shaped. In any of the examples ofFIGS. 15A through 15D, the distance between the centers of two adjacent slots112along the Y direction is set to λg/2. Depending on the purpose, however, it may be set to a value other than λg/2. The width direction of the central portion of each slot112substantially coincides with the width direction of the waveguide face122a(the X direction). As a result, an electromagnetic wave having a strong field component along the X direction can be transmitted or received. In each of the examples shown inFIGS. 15A through 15D, the position of each slot112along the X direction may be slightly altered so that the small-angle portion near the center is opposed to the waveguide face122a. Alternatively, each slot112may be rotated around an axis which is parallel to the Z axis, so that a polarized wave whose electric field oscillates along a direction that is inclined from the X direction is transmitted or received.

Next, an example of a slot array antenna including a plurality of waveguide members will be described.

FIG. 16is an upper plan view schematically showing the construction of a slot array antenna having a plurality of waveguide members122.FIG. 16shows relative positioning between a plurality of slots112and the plurality of waveguide members122and plurality of conductive rods124. The plurality of waveguide members of the slot array antenna in this example include two adjacent waveguide members122. The number of waveguide members122is not limited to two as illustrated, but may be a further greater number.

In the following description, regarding the two waveguide members122shown inFIG. 16, the left waveguide member122may be referred to as the “first waveguide member”, and the right waveguide member122as the “second waveguide member”. The first conductive member110has a plurality of slots112that are arranged along the first waveguide member and a plurality of slots112that are arranged along the second waveguide member.

With such construction, a slot array antenna having a plurality of slots112arranged in a two-dimensional array can be realized. From each slot112, an electromagnetic wave having a strong field component along the X direction or a direction that is inclined by an angle which is smaller than 45 degrees from the X direction can be transmitted or received.

Next, example embodiments of slot array antennas having a plurality of waveguide members122will be described.

FIG. 17Ais an upper plan view of a slot array antenna300according to an illustrative example embodiment as viewed from the +Z direction.FIG. 17Bis cross-sectional view taken along line B-B inFIG. 17A. The slot array antenna300includes: a first conductive member110; a second conductive member120; a third conductive member130; a plurality of waveguide members122U and a plurality of conductive rods124U on the second conductive member120; and a waveguide member122L and a plurality of conductive rods124L on the third conductive member130. The first conductive member110, the second conductive member120, and the third conductive member130are layered in this order, with gaps therebetween. InFIG. 17B, for ease of understanding, the plurality of waveguide members122U and122L are shown hatched.

The first conductive member110has a first conductive surface110bon the front side and a second conductive surface110aon the rear side. The second conductive member120has a third conductive surface120aon the front side, which is opposed to the second conductive surface110a, and a fourth conductive surface120bon the opposite side. The third conductive member130has a fifth conductive surface130aon the front side, which is opposed to the fourth conductive surface120b. As used herein, “the front side” means the side at which an electromagnetic wave is radiated or the side at which an electromagnetic wave arrives, whereas “the rear side” means the opposite side to the front side.

In the slot array antenna300shown, a first waveguide device100aand a second waveguide device100bare layered upon each other. The first waveguide device100aincludes the plurality of waveguide members122U directly coupling to a plurality of slots112. The second waveguide device100bincludes the waveguide member122L coupling to the plurality of waveguide members122U of the first waveguide device100a. The waveguide member122L and each conductive rod124L of the second waveguide device100bare disposed on the third conductive member130. The second waveguide device100bis basically similar in construction to the first waveguide device100a.

As shown inFIG. 17A, the first conductive member110has the plurality of slots112, which are arranged along the first direction (the Y direction) and along a second direction (the X direction) that intersects (e.g., being orthogonal in this example) the first direction. The waveguide face122aof each waveguide member122U extends along the Y direction. The waveguide face122aof each waveguide member122U couples to a first slot group (corresponding to the aforementioned first type of slots) including six slots that are arranged along the Y direction and a second slot group (corresponding to the aforementioned second type of slots) including six slots that are arranged along the Y direction, among the plurality of slots112. Although the conductive member110in this example has 48 slots112, the number of slots112is not limited to this example. Moreover, the shape and position of each slot112is not limited to this example. The interval between the centers of any two adjacent waveguide faces122amay be set to be shorter than the wavelength λo, and more preferably, shorter than the wavelength λo/2, for example.

FIG. 17Cis a diagram showing a planar layout of the plurality of waveguide members122U in the first waveguide device100a.FIG. 17Dis a diagram showing a planar layout of a waveguide member122L in the second waveguide device100b. As is clear from these figures, the waveguide members122U of the first waveguide device100aextend linearly, and include no branching portions or bends; on the other hand, the waveguide member122L of the second waveguide device100bincludes both branching portions and bends. The combination of the “second conductive member120” and the “third conductive member140” in the second waveguide device100bcorresponds to the combination in the first waveguide device100aof the “first conductive member110” and the “second conductive member120”.

The waveguide members122U of the first waveguide device100acouple to the waveguide member122L of the second waveguide device100b, through ports (throughholes)145U that are provided in the second conductive member120. Stated otherwise, an electromagnetic wave which has propagated through the waveguide member122L of the second waveguide device100bpasses through a port145U to reach a waveguide member122U of the first waveguide device100a, and propagates through the waveguide member122U of the first waveguide device100a. In this case, each slot112functions as a radiating element to allow an electromagnetic wave which has propagated through the waveguide to be radiated into space. Conversely, when an electromagnetic wave which has propagated in space impinges on a slot112, the electromagnetic wave couples to the waveguide member122U of the first waveguide device100athat lies directly under that slot112, and propagates through the waveguide member122U. An electromagnetic wave which has propagated through a waveguide member122U may also pass through a port145U to reach the waveguide member122L of the second waveguide device100b, and propagates through the waveguide member122L. Via a port145L of the third conductive member130, the waveguide member122L of the second waveguide device100bmay couple to an external waveguide device or an electronic circuit (e.g., a radio frequency circuit). As one example,FIG. 17Dillustrates an electronic circuit310which is connected to the port145L. Without being limited to a specific position, the electronic circuit310may be provided at any arbitrary position. The electronic circuit310may be provided on a circuit board which is on the rear surface side (i.e., the lower side inFIG. 17B) of the third conductive member130, for example. Such an electronic circuit310may include a microwave integrated circuit, e.g. an MMIC (Monolithic Microwave Integrated Circuit) that generates millimeter waves, for example. In addition to the microwave integrated circuit, the electronic circuit310may further include another circuit, e.g., a signal processing circuit. Such a signal processing circuit may be configured to execute various processes that are necessary for the operation of a radar system that includes a slot antenna array, for example. The electronic circuit310may include a communication circuit. The communication circuit may be configured to execute various processes that are necessary for the operation of a communication system that includes a slot antenna array.

The first conductive member110shown inFIG. 17Amay be called a “radiation layer”. The entirety of the second conductive member120, the plurality of waveguide members122U, and the plurality of conductive rods124U shown inFIG. 17Dmay be called an “excitation layer”. The entirety of the third conductive member130, the waveguide member122L, and the plurality of conductive rods124L shown inFIG. 17Dmay be called a “distribution layer”. Moreover, the “excitation layer” and the “distribution layer” may be collectively called a “feeding layer”. Each of the “radiation layer”, the “excitation layer”, and the “distribution layer” can be mass-produced by processing a single metal plate. The radiation layer, the excitation layer, the distribution layer, and any electronic circuitry to be provided on the rear face side of the distribution layer may be produced as a single-module product.

In the array antenna of this example, as can be seen fromFIG. 17B, a radiation layer, an excitation layer, and a distribution layer are layered, which are in plate form. Therefore, a flat and low-profile flat panel antenna is realized as a whole. For example, the height (thickness) of a multilayer structure having a cross-sectional construction as shown inFIG. 17Bcan be 10 mm or less.

With the waveguide member122L shown inFIG. 17D, the distances from the port145L of the third conductive member130to the respective ports145U (seeFIG. 17C) of the second conductive member120as measured along the waveguide are all set to an identical value. Therefore, a signal wave which is input to the waveguide member122L reaches the four ports145U of the second conductive member120all in the same phase, from the port145L of the third conductive member130. As a result, the four waveguide members122U on the second conductive member120can be excited in the same phase.

Depending on the purpose, it is not necessary for all slots112functioning as antenna elements to radiate electromagnetic waves in the same phase. InFIG. 17D, the distances from the port145L of the third conductive member130to the respective ports145U of the second conductive member120shown inFIG. 17C, as measured along the waveguide, may differ from one another. The network patterns of the waveguide members122U and122L in the excitation layer and the distribution layer may be arbitrary, without being limited to what is shown.

The electronic circuit310is connected to a waveguide extending above each waveguide member122U in the excitation layer, via the ports145U and145L shown inFIG. 17CandFIG. 17D. A signal wave which is output from the electronic circuit310is subject to branching in the distribution layer, and then propagates on the plurality of waveguide members122U in the excitation layer, until reaching the plurality of slots112. In order to ensure that the signal waves have an equal phase at the positions of two adjacent slots112along the X direction, the total waveguide lengths from the electronic circuit310to the two adjacent slots112along the X direction may be designed to be substantially equal, for example.

Although the present example embodiment illustrates that four waveguide members122U are provided on the second conductive member120, the number of waveguide members122U may be any arbitrary number which is one or greater. The number of rows of slots112in the first conductive member110is to be determined based on the number of waveguide members122U. When there is one waveguide member122U, the first conductive member110may only include two rows of slots in a staggered arrangement (a first slot group and a second slot group) coupling to that waveguide member122U. This similarly applies to the following example embodiments.

Next, other example embodiments of the present disclosure will be described.

FIG. 18Ais a plan view showing a slot array antenna300A according to another example embodiment of the present disclosure.FIG. 18Bis a side view showing the slot array antenna300A as viewed from the −Y direction. The slot array antenna300A includes a first conductive member110, a second conductive member120, and a third conductive member130, which are layered with gaps therebetween. On the second conductive member120, a plurality of waveguide members122U and a plurality of conductive rods124U are disposed. On the third conductive member120, too, a plurality of waveguide members122L and a plurality of conductive rods124L are disposed. The first conductive member110constitutes a radiation layer210. The second conductive member120and the plurality of waveguide members122U and plurality of conductive rods124U thereon constitute an excitation layer220. The third conductive member130and the plurality of waveguide members122L and the plurality of conductive rods124L thereon constitute a distribution layer230. Each conductive member110,120or130may be shaped by processing a metal plate, for example. Alternatively, each conductive member110,120or130may be produced by plating a shaped piece of resin (plastic).

FIG. 19Ais a cross-sectional view showing enlarged a part of the construction of the radiation layer210and the excitation layer220. As shown inFIG. 19A, the rows of waveguide members122U and the rows of conductive rods124U upon the second conductive member120alternate along the X direction. In this example, the height of each waveguide member122U (i.e., the dimension along the Z direction) is smaller than the height of each conductive rod. With such structure, isolation between signal waves propagating along the respective waveguide members122U can be enhanced.

FIG. 19Bis a diagram showing enlarged a part of the radiation layer210. The first conductive member110constituting the radiation layer210has a plurality of slots112. The plurality of slots112constitute a plurality of slot sequences.

Each slot sequence includes a first slot group and a second slot group each of which extends along the first direction (the Y direction). A first slot group includes a plurality of slots112arranged along the Y direction. A second slot group also includes a plurality of slots112arranged along the Y direction. Each second slot group lies next to a first slot group. The position of each slot in a first slot group regarding the Y direction is different from the position of each slot in a second slot group regarding the Y direction. Along the Y direction, the center of (each of) one or more slots in a first slot group is located between two adjacent slots in a second slot group. Similarly, along the Y direction, the center of (each of) one or more slots in a second slot group is located between two adjacent slots in a first slot group. In the example ofFIG. 18A, the position of any first slot group along the Y direction is offset from the position of any second slot group along the Y direction by a length corresponding to a half of the wavelength of an electromagnetic wave within the waveguide. The first slot group and the second slot group are arrayed in a “staggered arrangement” as aforementioned.

FIG. 19Bshows, with a broken line, a center line C of a waveguide face of a waveguide member that is the closest to a given first slot group and a given second slot group. As in the example ofFIG. 19B, the distance from the center line C to each slot may differ from slot to slot. In the example ofFIG. 19B, the closer to the end of the slot sequence, the closer to the center line C of the waveguide face the slot becomes. Moreover, the slots do not need to be identical in shape and width, either; they may vary in shape and width depending on the position within the slot sequence. By additionally introducing such characteristics to the first slot group and the second slot group, the radiation pattern from the slot antenna can be adjusted. In the case where the distance of each slot from the center line C varies depending on the position within the slot group, the direction along which the slots flank one another to constitute that slot group does not strictly coincide with the direction that the waveguide face extends. However, so long as the shifts in the slot sequence position remains less than twice the width of the waveguide face, it is said in the present specification that the slots are arranged along the direction that the waveguide face extends.

The first conductive surface110bof the first conductive member110on the front side has a shape defining a plurality of horns114flanking one another along the X direction. Each horn114is structured so as to extend along the first direction (the Y direction). Each horn114has a pair of electrically-conductive wall faces114a(hereinafter also referred to as electrically conductive walls114a) rising from the first conductive surface110band extending along the first direction. When viewed from a direction which is perpendicular to the first conductive surface110b, a first slot group and a second slot group are located between the pair of wall faces114a. In this example, the plurality of horns114each accommodate a plurality of slot sequences; in other words, each horn114accommodates a first slot group and a second slot group. As used herein, that “a horn114accommodates a slot sequence” means that the slot sequence is surrounded by the electrically conductive walls of the horn114.

The plurality of horns114are arranged so as to flank one another along the second direction (the X direction). In the example ofFIG. 18A, eight rows of horns114are provided. With such structure, electromagnetic waves of different phases can be radiated from the slots112within the plurality of horns114.

As shown inFIG. 19B, each horn114includes the pair of electrically conductive walls114aextending along the longitudinal direction. Each electrically conductive wall114ahas a shape resembling a staircase (convex form). Without being limited to a staircase, the shape of the electrically conductive wall114amay be an inclined plane, for example.

At the bottom of each horn114, a plurality of slots112(a first slot group and a second slot group) are provided. The shape of the opening of each slot112according to the present example embodiment is rectangular, and its longitudinal direction coincides with the Y direction. However, without being limited to such a shape and arrangement, adjustments are possible in accordance with the required antenna characteristics.

FIG. 20Ais a plan view showing the excitation layer220.FIG. 20Bis a perspective view showing enlarged a part of the excitation layer220.FIG. 20Cis a plan view showing enlarged a part of the excitation layer220. The excitation layer220includes the second conductive member120as well as the plurality of waveguide members122U and the plurality of conductive rods124U thereon. In the central portion of each waveguide member122U, the second conductive member120has a port145U (throughhole) to serve as a feeding point. Hereinafter, the port145U may be referred to as a “feeding slot”. The opening of the port145U is shaped so as to include a lateral portion extending along the X direction and a pair of vertical portions extending along the Y direction from both ends of the lateral portion. In this example, the pair of vertical portions extend in mutually opposite directions from both ends of the lateral portion. The plurality of waveguide members122U are arranged along the X direction. The waveguide face of each waveguide member122U has a plurality of dents (recesses) near the port145U and near both ends of the waveguide face. The position and depth of each dent are appropriately designed so as to achieve desired radiation characteristics or reception characteristics. The plurality of conductive rods124U constitute a plurality of rod rows extending alongside the plurality of waveguide members122U. In this example, one rod row is provided between two adjacent waveguide members122U.

As shown inFIG. 20B, the shape of each conductive rod124U as viewed from the +Z direction is rectangular. As compared to the case where the shape is a square, each rod124U has a smaller dimension along the Y direction. Moreover, the width of any interspace between two adjacent rods124U along the Y direction may be set to a range of λm/10 or less, for example. As a result, the period of arrangement of the rods124U along the Y direction (i.e., the distance between the centers of adjacent rods) can be set to a value which is equal to or greater than λm/9 and smaller than λm/5. With such an interval of arrangement, leakage of a radio frequency signal propagating along the waveguide members122U can be prevented.

FIG. 20Dis a diagram for describing relative positioning between a port145U in the second conductive member120and a slot112A included in a first slot group and a slot112B included in a second slot group on the first conductive member110. As illustrated, when viewed from a direction which is perpendicular to the waveguide face of the waveguide member122U (the +Z direction), the center of each slot112A in the first slot group is located on one side (i.e., the left side in this figure) of a line C extending through the center of the waveguide face (referred to as the “center line”), whereas the center of each slot in the second slot group is located on another side of the center line C of the waveguide face (i.e., the right side in this figure). Another way of expressing this relative positioning may be that the center line C passes between a row constituted by the centers of the slots in the first slot group and a row constituted by the centers of the slots in the second slot group. When viewed from the +Z direction, the distance from the center of each slot in the first slot group or the second slot group to the center line C of the waveguide face is shorter than the distance between the center line C of the waveguide face and the center of the conductive rod124U that is the closest to the center line C. Similarly, when viewed from the +Z direction, the center of the port145U is located between the slot112A included in the first slot group and the slot112B included in the second slot group. More specifically, when viewed from a direction perpendicular to the waveguide face, the center of the port145U is located between a central portion of a region in which the first slot group is distributed and a central portion of a region in which the second slot group is distributed. Although the present example embodiment illustrates that the port145U overlaps neither slot, the port145U may overlap at least one of them.

As shown inFIG. 20D, in this example, the opening of each port145U is shaped so as to include: a lateral portion1451extending along the second direction (the X direction) that intersects the first direction (the Y direction); a first vertical portion145t1extending along the Y direction and being connected to one end of the lateral portion1451; and a second vertical portion145t2extending along the Y direction and being connected to another end of the lateral portion1451. Note that the direction that the vertical portions145t1and145t2extend may not be orthogonal to the direction that the lateral portion1451extends. When the first direction (the +Y direction) is regarded as a positive direction and an opposite direction (the −Y direction) of the first direction is regarded as a negative direction, a positive end145p1of the first vertical portion145t1is closer to the lateral portion1451than is a negative end145n1of the first vertical portion145t1. Moreover, a negative end145n2of the second vertical portion145t2is closer to the lateral portion1451than is a positive end145p2of the second vertical portion145t2. The positive end145p1of the first vertical portion145t1has a smaller distance to the center of the slot112A in the first slot group that is the closest to the lateral portion1451than does the negative end145n1of the first vertical portion145t1. Moreover, the negative end145n2of the second vertical portion145t2has a smaller distance to the center of the slot112B in the second slot group that is the closest to the lateral portion1451than does the positive end145p2of the second vertical portion145t2.

In the example ofFIG. 20D, along the first direction (the Y direction), the first vertical portion145t1has a partial overlap with the closest slot112B in the second slot group. Moreover, along the Y direction, the second vertical portion145t2has a partial overlap with the closest slot112A in the first slot group. Without being such structure, the slots and throughholes (ports) may be arranged in any manner so that, along the Y direction, at least one of the first vertical portion145t1and the second vertical portion145t2has at least a partial overlap with at least one slot included in the first slot group and the second slot group.

Although the present example embodiment illustrates that the opening of each slot112as viewed from the +Z direction has a rectangular shape (I shape) extending along the Y direction, it may have other shapes as illustrated inFIGS. 10A through 10E. The arrangement of the slots112is also not limited to the illustrated example; various arrangements are possible, as has been described with reference to e.g.FIGS. 11A through 11E. In example embodiments of the present disclosure, the opening of each slot in the first slot groups and the second slot groups has, in at least a central portion thereof, a shape extending along the Y direction or along a direction that is inclined by an angle which is smaller than 45 degrees from the Y direction. With such construction, an electromagnetic wave having a greater field component along the X direction than along the Y direction can be radiated. It is not necessary that the plurality of slots112are all in the same orientation, either. Depending on the desired radiation characteristics or reception characteristics, implementations in which the plurality of slots112have respectively different orientations may also be possible. Moreover, the plurality of slots included in each first slot group or each second slot group may not be at equal interval along the Y direction.

When viewed from a direction perpendicular to the waveguide face, each port145U is located in a central portion of the corresponding waveguide member122U, and located between the central portion of the first slot group and the central portion of the second slot group. The position of each port145U may be shifted from the central portion of the waveguide member122U.

FIG. 21Ais a plan view showing a construction for the distribution layer230.FIG. 21Bis a diagram showing enlarged a part of the distribution layer230. The third conductive member130in the distribution layer230has plurality of ports145L (throughholes). In this example, there are eight ports145L. The ports145L are arranged along the X direction, while being shifted in position along the Y direction.

On the conductive surface130aof the third conductive member130, the plurality of waveguide members122L and the plurality of conductive rods124L are disposed. The plurality of waveguide members122L are respectively connected to the plurality of ports145L at one end. Each of the plurality of waveguide members122L is independent, and has one or more bends. Each waveguide member122L extends from the port145L to a position opposed to the corresponding port145U in the second conductive member120, along a path having a respectively different length. With such construction, electromagnetic waves of different phases can be supplied to the plurality of ports145U in the second conductive member120.

The plurality of conductive rods124L are arranged in a two-dimensional array along the X direction and along the Y direction. The conductive rods124L surround each port145L and each waveguide member122L. Via a waveguide not shown, each port145L is to be connected to a terminal of an electronic circuit including a microwave integrated circuit such as an MMIC. In other words, via the plurality of ports145L, the electronic circuit is connected to the waveguides extending between the waveguide members122L and the second conductive member120. Note that a structure for connecting an electronic circuit and a waveguide is disclosed in US Patent Application Publication Nos. 2018-0351261, 2019-0006743, 2019-0139914, 2019-0067780, and 2019-0140344, and International Patent Application Publication No. 2018/105513, for example. The entire disclosure of these publications is incorporated herein by reference.

As shown inFIG. 21B, each waveguide member122L has a dent(s) at a bend(s). Moreover, a recess is made in one end of each waveguide member122L that is connected to a port145L. Each waveguide member122L also has one or more bumps. Such a dent(s) and a bump(s) are provided so that an impedance of the waveguide extending between each waveguide member122L and the second conductive member120and an impedance of the port145U in the second conductive member120will match each other. Such a dent(s) and a bump(s) suppress reflection of signal waves.

FIG. 22Ais a cross-sectional view of the slot array antenna300A taken along a plane which passes through the center of one waveguide member122U on the second conductive member120and which is parallel to the YZ plane.FIG. 22Bis a diagram showing enlarged a part of the structure shown inFIG. 22A. The waveguide member122U is split in two portions by the port145U. The two portions will be referred to as a first ridge122U1and a second ridge122U2. The first ridge122U1and the second ridge122U2each have a pair of electrically-conductive end faces122e, which are opposed to each other via the port145U. The pair of end faces122eof the first ridge122U1and the second ridge122U2and the port145U define a hollow waveguide. Among the slots in the first slot group and the second slot group, a number of slots that are arranged along the first ridge122U1are connected to the waveguide within the port145U and the waveguide in the underlying layer, via the first waveguide extending between the waveguide face of the first ridge122U1and the second conductive surface on the rear side of the first conductive member110. Similarly, among the slots in the first slot group and the second slot group, the remaining slots that are arranged along the second ridge122U2are connected to the waveguide in the port145U and the waveguide in the underlying layer, via the second waveguide extending between the waveguide face of the second ridge122U2and the second conductive surface on the rear side of the first conductive member110. The waveguide in the underlying layer as referred to in this example is a ridge waveguide that is created between the waveguide face of the waveguide member122L and the fourth conductive surface on the rear side of the second conductive member120. Without being limited to a ridge waveguide, the waveguide in the underlying layer of the port145U may be any other waveguide, e.g., a hollow waveguide.

According to the present example embodiment, a single feeding point in each slot sequence exists, only at one place along the way (e.g., in the center) of the slot sequence. Through the port145U, feeding occurs from one place at a midpoint between the first and second slot groups, to each slot in the first and second slot groups. An electromagnetic wave which is supplied from the port145U serving as a feeding slot can be radiated from each slot as a laterally polarized wave or an obliquely polarized wave. As compared to a construction where feeding occurs from both ends of a slot sequence, the device construction can be simplified. More-over, the device can be downsized as compared to a slot array antenna in which a hollow waveguide is used. Therefore, even in the case where high-frequency electromagnetic waves such as millimeter waves are used, good radiation characteristics or reception characteristics can be achieved.

Next, a variant of the present example embodiment will be described.

FIG. 23is diagram showing a slot array antenna300B according to this variant.FIG. 24Ais a plan view showing an excitation layer220according to this variant.FIG. 24Bis a diagram showing enlarged a part of the excitation layer220in this variant. This variant differs from the above-described example embodiment in that the opening of each of the plurality of ports145U in the second conductive member120is H-shaped; otherwise, it is similar to the above-described example embodiment.

FIG. 24Cis a diagram for describing relative positioning between respective elements in this variant. InFIG. 24C, the waveguide members122U, the conductive rods124U, and the ports145U in the excitation layer220are shown with solid lines. The slots122A and122B in the radiation layer210and electrically conductive walls114aof the horns114are shown with dotted lines. The conductive rods124L in the distribution layer230are shown with broken lines. Note that the waveguide members122L in the distribution layer230are not shown inFIG. 24C.

The opening of each port145U in this example has an H shape that includes a lateral portion1451, a first vertical portion145t1, and a second vertical portion145t2. One end of the lateral portion1451is located between both ends of the first vertical portion145t1, whereas another end of the lateral portion1451is located between both ends of the second vertical portion145t2.

In this example, the slots112A in the first slot group and the slots112B in the second slot group, which are in a staggered arrangement, slightly overlap the ports145U which are located below. The ports145U feed an electromagnetic wave. Moreover, the conductive rods124L in the distribution layer230and the ports145U slightly overlap. As a result, in see-through view to the central slots112A and112B from the +Z direction, ends of the ports145U are visible, as illustrated inFIG. 23. When an electromagnetic wave passes through a port145U, a strong electric field will occur in the central portion thereof, whereas only a minute electric field will occur in the periphery. Therefore, even if overlaps exist between ends of the ports145U and ends of the slots112A and112B, the antenna functionality is not necessary undermined. Such structure will allow the interval of arrangement between the slots112A and112B to be selected more freely, thus making it easy to improve the directivity of the slot array antenna300B. As in this example, when viewed from a direction perpendicular to the waveguide face of the waveguide member122U, at least a portion of each port145U (throughhole) may over-lap at least one of: one slot included in the first slot group; and one slot included in the second slot group.

FIG. 24Dis a diagram showing another variant. In this example, the shape of each port145U differs from that in the example shown inFIG. 24C; otherwise, it is similar to the example ofFIG. 24C. In the example shown inFIG. 24D, too, the opening of each port145U is shaped so as to include: a lateral portion1451extending along the X direction; a first vertical portion145t1extending along the Y direction and being connected to one end of the lateral portion1451; and a second vertical portion145t2extending along the Y direction and being connected to another end of the lateral portion1451. The directions that the vertical portions145t1and145t2extend may not be orthogonal to the direction that the lateral portion1451extends. When the first direction (the +Y direction) is regarded as a positive direction and an opposite direction (the −Y direction) of the first direction is regarded as a negative direction, a negative end of the first vertical portion145t1is closer to the lateral portion1451than is the positive end of the first vertical portion145t1. Moreover, a positive end of the second vertical portion145t2is closer to the lateral portion1451than is a negative end of the second vertical portion145t2. When viewed from a direction perpendicular to the waveguide face of the waveguide member122U, the positive end of the first vertical portion145t1at least partially overlaps the slot112A in the first slot group that is the closest to the lateral portion1451, and the negative end of the second vertical portion145t2at least partially overlaps the slot112B in the second slot group that is the closest to the lateral portion. With such construction, too, characteristics similar to those of the aforementioned construction are obtained.

The slot array antenna in each of the example embodiments that have been described with reference toFIGS. 17A through 24Dhas a plurality of sets each including a combination of a first slot group, a second slot group, a waveguide member122U, and a throughhole (port145U). The plurality of sets of combinations are arranged along the X direction, which intersects the first direction (the Y direction). The plurality of conductive rods124U are located around each waveguide member122U. Example embodiments of the present disclosure are not limited to such an implementation. For example, the slot array antenna may only include a single combination of a first slot group, a second slot group, a waveguide member122U, and a throughhole (port145U). Moreover, when constructing an excitation layer and a distribution layer, various circuit elements in waveguides can be utilized. Examples thereof are disclosed in U.S. Pat. Nos. 10,042,045, 10,090,600, 1,015,8158, International Patent Application Publication No. 2018/207796, International Patent Application Publication No. 2018/207838, and US Patent Application Publication No. 2019-0074569, for example. The entire disclosure of these publications is incorporated herein by reference.

A slot array antenna according to an example embodiment of the present disclosure can be suitably used in a radar device or a radar system to be incorporated in moving entities such as vehicles, marine vessels, aircraft, robots, or the like, for example. A radar device would include a slot array antenna according to an example embodiment of the present disclosure and a microwave integrated circuit, e.g., MMIC, that is connected to the slot array antenna. A radar system would include the radar device and a signal processing circuit that is connected to the microwave integrated circuit of the radar device. The signal processing circuit may be configured to estimate an azimuth of each arriving wave by executing an algorithm such as the MUSIC method, the ESPRIT method, or the SAGE method, and output a signal indicating the estimation result. The signal processing circuit may further be configured to estimate the distance to each target as a wave source of an arriving wave, the relative velocity of the target, and the azimuth of the target by using a known algorithm, and output a signal indicating the estimation result.

In the present disclosure, the term “signal processing circuit” is not limited to a single circuit, but encompasses any implementation in which a combination of plural circuits is conceptually regarded as a single functional part. The signal processing circuit may be realized by one or more System-on-Chips (SoCs). For example, a part or a whole of the signal processing circuit may be an FPGA (Field-Programmable Gate Array), which is a programmable logic device (PLD). In that case, the signal processing circuit includes a plurality of computation elements (e.g., general-purpose logics and multipliers) and a plurality of memory elements (e.g., look-up tables or memory blocks). Alternatively, the signal processing circuit may be a set of a general-purpose processor(s) and a main memory device(s). The signal processing circuit may be a circuit which includes a processor core(s) and a memory device(s). These may function as the signal processing circuit.

A slot antenna array according to an example embodiment of the present disclosure includes a waffle iron structure which permits downsizing, and thus allows the area of the face on which antenna elements are arrayed to be significantly reduced, as com-pared to conventional constructions. Therefore, a radar system incorporating the slot array antenna can be easily mounted in a narrow place such as a face of a rearview mirror in a vehicle that is opposite to its specular surface, or a small-sized moving entity such as a UAV (an Unmanned Aerial Vehicle, a so-called drone). Note that, without being limited to the implementation where it is mounted in a vehicle, a radar system may be used while being fixed on the road or a building, for example.

A slot array antenna according to an example embodiment of the present disclosure can also be used in a wireless communication system. Such a wireless communication system would include a slot array antenna according to any of the above example embodiments and a communication circuit (a transmission circuit or a reception circuit) that is connected to the slot array antenna. The transmission circuit may be, for example, configured to supply a signal wave representing a signal for transmission to a waveguide within the slot array antenna. The reception circuit may be con-figured to demodulate a signal wave which has been received via the slot array antenna, and output it as an analog or digital signal.

A slot array antenna according to an example embodiment of the present disclosure can further be used as an antenna in an indoor positioning system (IPS). An indoor positioning system is able to identify the position of a moving entity, such as a person or an automated guided vehicle (AGV), that is in a building. A slot array antenna can also be used as a radio wave transmitter (beacon) for use in a system which provides information to an information terminal device (e.g., a smartphone) that is carried by a person who has visited a store or any other facility. In such a system, once every several seconds, a beacon may radiate an electromagnetic wave carrying an ID or other information super-posed thereon, for example. When the information terminal device receives this electromagnetic wave, the information terminal de-vice transmits the received information to a remote server computer via telecommunication lines. Based on the information that has been received from the information terminal device, the server computer identifies the position of that information terminal de-vice, and provides information which is associated with that position (e.g., product information or a coupon) to the information terminal device.

Application examples of a radar system, a communication system, and various monitoring systems including a slot array antenna having a WRG structure are disclosed in the specification of U.S. Pat. No. 9,786,995 and the specification of U.S. Pat. No. 10,027,032, for example. The entire disclosure of these publications is incorporated herein by reference. A slot array antenna according to the present disclosure is applicable to each application example that is disclosed in these publications.

A slot array antenna according to the present disclosure is usable in any technological field that utilizes electromagnetic waves. For example, it is available to various applications where transmission/reception of electromagnetic waves of the gigahertz band or the terahertz band is performed. In particular, they may be suitably used in onboard radar systems, various types of monitoring systems, indoor positioning systems, wireless communication systems, etc., where downsizing is desired.

This application is based on Japanese Patent Applications No. 2018-113890 filed on Jun. 14, 2018, the entire contents of which are hereby incorporated by reference.