TRANSMISSION DEVICE AND ANTENNA

A transmission device including: a transmission substrate for transmitting a signal, the transmission substrate including a feeding line and a capacitive coupling conductor that are provided on one side of a plate-shaped dielectric substrate and a ground conductor that is provided on other side of the dielectric substrate; and a connector for inputting and outputting a signal, the connector including an inner conductor and an outer conductor that is provided outside of the inner conductor, wherein the connector is provided on the one side of the dielectric substrate on which the feeding line and the capacitive coupling conductor of the transmission substrate are provided, and the inner conductor of the connector is connected to the feeding line, the outer conductor is connected to the capacitive coupling conductor, and the ground conductor of the transmission substrate is not connected to the outer conductor of the connector.

TECHNICAL FIELD

The present disclosure relates to a transmission device and an antenna.

BACKGROUND ART

Patent document 1 describes a connection structure of a microstrip line which includes a center conductor with a predetermined width arranged on one side of a substrate and a ground conductor arranged on the other side of the substrate, wherein an earth pattern connected to the ground conductor is formed on a conductor arrangement surface where the center conductor of the substrate is arranged, a connector with a connector inner conductor and a connector outer conductor is installed to the conductor arrangement surface, the connector inner conductor is connected to the center conductor of the microstrip line, and the connector outer conductor is connected to the earth pattern.

CITATION LIST

Patent Literature

[Patent Document 1] Microfilm of Japanese Utility Model Application No. H01-140181 (Japanese Unexamined Utility Model Application Publication No. H03-079510)

SUMMARY OF INVENTION

Technical Problem

By the way, in a microstrip antenna or the like, a transmission device which includes a feeding line on one side of a dielectric substrate and a transmission substrate (a so-called printed circuit board) and a connector on the other side of the dielectric substrate is used. Here, a radiating element that transmits and receives radio waves is connected to the feeding line, a ground conductor is provided to the transmission substrate, and the connector is connected with a coaxial cable and serves as a signal input/output: terminal. Connectors with a small outer dimension such as SMPM (Sub Miniature Push-on Mini) are mounted on a side of the transmission substrate where the feeding line is provided. For this reason, an outer conductor of the connector and the ground conductor of the transmission substrate have been connected via a through-hole or the like in the dielectric substrate whose inside is covered with a conductor. However, the provision of the through-hole or the like increases the manufacturing cost of the transmission device. Therefore, it is required not to provide the through-hole or the like that connects the outer conductor of the connector with the ground conductor of the transmission substrate.

The present invention provides a transmission device or the like that can operate without connecting the ground conductor of the transmission substrate with the outer conductor of the connector.

Solution to Problem

The invention recited in claim1is a transmission device including: a transmission substrate for transmitting a signal, the transmission substrate including a feeding line and a capacitive coupling conductor that are provided on one side of a plate-shaped dielectric substrate and a ground conductor that is provided on other side of the dielectric substrate; and a connector for inputting and outputting a signal, the connector including an inner conductor and an outer conductor that is provided outside of the inner conductor, wherein the connector is provided on the one side of the dielectric substrate on which the feeding line and the capacitive coupling conductor of the transmission substrate are provided, and the inner conductor of the connector is connected to the feeding line, the outer conductor is connected to the capacitive coupling conductor, and the ground conductor of the transmission substrate is not connected to the outer conductor of the connector.

The invention recited in claim2is the transmission device according to claim1, wherein, in the transmission substrate, the capacitive coupling conductor and the ground conductor face each other via the dielectric substrate.

The invention recited in claim3is the transmission device according to claim2, wherein the ground conductor of the transmission substrate and the outer conductor of the connector are capacitively coupled.

The invention recited in claim4is the transmission device according to any one of claims1to3, wherein, in the capacitive coupling conductor, an opening is formed at a center portion and a gap is formed from an outer edge to the opening, and an end of the feeding line is located at the gap.

The invention recited in claim5is the transmission device according to any one of claims1to4, wherein a shape surrounding the outer edge of the capacitive coupling conductor is any one of polygonal, circular and oval.

The invention recited in claim6is the transmission device according to any one of claims1to5, wherein a dimension from a center of the connector to an outer edge of the capacitive coupling conductor is more than ¼ and less than ½ of an effective wavelength in the dielectric substrate.

The invention recited in claim7is the transmission device according to any one of claims1to5, wherein, among a dimension from a center of the connector to an outer edge of the capacitive coupling conductor, the transmission device transmits a signal with a lower limit of a frequency at which a minimum dimension corresponds to ¼ of an effective wavelength and with an upper limit of a frequency at which a maximum dimension corresponds to ½ of the effective wavelength.

The invention recited in claim8is an antenna including: a radiating element transmitting and receiving radio waves; and a transmission device according to any one of claims1to7which the radiating element is connected to and transmits a signal based on the radio waves transmitted and received by the radiating element.

The invention recited in claim9is the antenna according to claim8, wherein, among a dimension from a center of the connector to an outer edge of the capacitive coupling conductor, the radiating element transmits and receives radio waves with a lower limit of a frequency at which a minimum dimension corresponds to ¼ of an effective wavelength and with an upper limit of a frequency at which a maximum dimension corresponds to ½ of the effective wavelength.

Effect of the Invention

According to the invention recited in claims1and8, the transmission device or the antenna can operate without connecting the ground conductor of the transmission substrate with the outer conductor of the connector.

According to the invention recited in claim2, compared to the case of not facing each other, coupling capacitance can be increased.

According to the invention recited in claim3, a DC connection is not required.

According to the invention recited in claim4, the transmission device can be composed of a single conductor layer.

According to the invention recited in claim5, the transmission device can have a shape according to the purpose.

According to the invention recited in claim6, a shape of the capacitive coupling conductor can be set based on the effective wavelength.

According to the invention recited in claims7and9, a shape of the capacitive coupling conductor can be set based on a frequency band.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the exemplary embodiment, a microstrip antenna is used as an example to describe a transmission device. A transmission device is a device that transmits a signal, and a coaxial cable is connected to the signal input/output via a connector. A transmission device does not include an antenna element. Therefore, the transmission device may be used as a microstrip antenna by being connected with an antenna element, or may be used as a filter by being connected with a filter element that extracts a specific frequency signal from the signal. Furthermore, elements with other functions may be connected to the transmission device.

FIGS.1A and1Billustrate a microstrip antenna in a millimeter wave band.FIG.1Aillustrates a microstrip antenna1using a connector120with a small outer dimension, andFIG.1Billustrates a microstrip antenna2using a connector220with a large outer dimension. InFIG.1A, the microstrip antenna1is shown at an upper side of the paper and a perspective view of the connector120is shown at a lower side of the paper. Similarly, inFIG.1B, the microstrip antenna2is shown at the upper side of the paper and a perspective view of the connector220is shown at the lower side of the paper. In the microstrip antenna1inFIG.1A, a direction to the right of the paper is referred to as x direction, a direction to the upper side of the paper is referred to as y direction, and a direction to a surface of the paper is referred to as z direction. The same is applied to the microstrip antenna2inFIG.1B. Here, it is assumed that the microstrip antenna1and the microstrip antenna2transmit and receive radio waves in the millimeter wave band.

The microstrip antenna1shown inFIG.1Aincludes a transmission device100and a radiating element300. The transmission device100includes a transmission substrate110and the connector120. The transmission substrate110includes a plate-shaped dielectric substrate111, a feeding line112provided on one side of the dielectric substrate111(hereinafter referred to as a front surface), and a ground conductor113(only the sign thereof is denoted) provided on the other side of the dielectric substrate111back surface). The (hereinafter referred to as a transmission substrate110includes a capacitive coupling conductor114(seeFIG.2Aor the like described later) on the front surface, but illustration thereof is omitted inFIG.1A. The radiating element300is provided to be connected to the feeding line112of the dielectric substrate111. The radiating element300of the microstrip antenna1transmits and receives radio waves, and is just denoted here as radiating element300.

The dielectric substrate111is configured by, for example, impregnating a glass fabric base with epoxy resin, polyimide resin, fluorine resin or the like. The feeding line112and the ground conductor113are composed of conductors such as copper (Cu) foil. Here, the conductor means a conductor that is a good conductor of electricity. The feeding line112is provided on the front surface of the dielectric substrate111in a shape of a strip with a predetermined width. The width of the feeding line112is set according to a characteristic impedance with respect to the signal to be transmitted. The ground conductor113is provided to cover the entire back surface of the dielectric substrate111. The ground conductor113does not necessarily have to cover the entire back surface of the dielectric substrate111, but only needs to be provided to face the feeding line112. Here, the transmission substrate110is a dielectric substrate111in which a conductor such as copper (Cu) foil is provided on both sides and the copper foil is processed into the feeding line112and ground conductor113. In other words, the transmission substrate110includes the dielectric substrate111as well as the feeding line112and ground conductor113. The transmission substrate110is sometimes described as a printed circuit board. The configuration in which the feeding line112is provided on the front surface of the dielectric substrate111and the ground conductor113is provided on the back surface thereof may be described as a microstrip line.

The radiating element300shown inFIG.1Ais a so-called patch antenna, which has a radiating part and a ground plate. The radiating part is composed of a conductor on the front surface of the dielectric substrate111. InFIG.1A, a planar shape of the radiating section is square as one specific example. The ground conductor113is provided on the back surface of the dielectric substrate111to function as the ground plate. The ground conductor113is provided to face the radiating part. The radiating part is configured by processing the same conductor as the feeding line112. Hereinafter, the radiating part is referred to as the radiating element300, and description of the ground plate will be omitted. The radiating element300does not have to be a patch antenna as long as being connected to and fed by the feeding line112.

The microstrip antenna1shown inFIG.1Ahas nine radiating elements300on the front surface of the dielectric substrate111, three of which are arranged in the right direction on the paper (the x direction) and three of which are arranged in the upper direction on the paper (the y direction). The feeding line112connects the three radiating elements300in sequence in the upper direction on the paper (the y direction). The microstrip antenna1shown inFIG.1Aincludes three feeding lines112. One end of each of the feeding lines112(an end at the lower side on the paper and in the −y direction) is connected to the connector120. Here, the connector120is, for example, SMPM with a small outer dimension. If the outer dimension of the connector120is small, the connector120is arranged at the pitch of arrangement of the radiating elements300in the left-right direction on the paper (±x direction).

An antenna with multiple radiating elements, such as the microstrip antenna1, is used for wireless communication in MIMO (Multiple Input Multiple Output) method in which signals are transmitted simultaneously from multiple radiating elements on the transmitting side and the signals are received by multiple radiating elements on the receiving side to speed up communication, or used for shaping the shape of radiated radio waves (for example, beamforming or the like).

The microstrip antenna2shown inFIG.1Bincludes a transmission device200and a radiating element300. The transmission device200includes a transmission substrate210and a connector220. The transmission substrate210includes a dielectric substrate211, a feeding line212provided on a front surface of the dielectric substrate211, and a ground conductor213(only the sign thereof is denoted) provided on a back surface of the dielectric substrate211. The radiating element300is provided to be connected to the feeding line212of the dielectric substrate211.

The microstrip antenna2shown inFIG.1Bhas nine radiating elements300arranged on the front surface of the dielectric substrate211. The microstrip antenna2has three feeding lines212to connect the three radiating elements300in the upper direction on the paper (the y direction). One end of each of the feeding lines212(an end at the lower side on the paper and in the −y direction) is connected to the connector220. Since the microstrip antenna1and the microstrip antenna2transmit and receive radio waves in the same millimeter wave band, the shape and arrangement of the nine radiating elements300are the same as in the microstrip antenna1. Here, the connector220is, for example, SMA (Sub Miniature Type A) whose outer dimension is larger than the outer dimension of SMPM described above. As shown inFIG.1B, in a case where the outer dimension of the connector220is large, the connectors220are not arranged in a pitch as the arrangement of the radiating elements300in the left-right direction on the paper (±x direction). Therefore, the connectors220are arranged at a pitch larger than the pitch of the arrangement of the radiating elements300in a lateral direction (x direction) on the paper surface. Thus, the feeding lines212are configured to be bent to absorb the difference in pitch.

Based on the above description, the dielectric substrate211of the microstrip antenna2using the connector220with a large outer dimension is larger than the dielectric substrate111of the microstrip antenna1using the connector120with a small outer dimension. In addition, the feeding line212of the microstrip antenna2using the connector220with a large outer dimension is longer than the feeding line112of the microstrip antenna1using the connector120with a small outer dimension, which leads to a big loss. Therefore, it is preferable to use connectors with a small outer dimension for antennas that transmit and receive radio waves with short wavelengths such as the millimeter wave band.

As can be seen from the perspective view shown in the lower side ofFIG.1B, in the case of the connector220with a large outer dimension such as SMA, a through hole is provided in the dielectric substrate211, and the connector220is inserted and mounted from the back surface on which the ground conductor213of dielectric substrate211is provided. In other words, an outer conductor of the connector220contacts the ground conductor213, and an inner conductor (a core wire) of the connector220is connected to the feeding line212through the through hole.

On the other hand, as can be seen from the perspective view shown in the lower side ofFIG.1A, the connector120with a small outer dimension such as SMPM is mounted on the front surface of the dielectric substrate111, that is, the front surface where the feeding line112is provided. In other words, an outer conductor of the connector120and the ground conductor113provided on the dielectric substrate111are placed on different surfaces of the transmission substrate110. Therefore, the outer conductor of the connector120and the ground conductor113of the transmission substrate110were connected via a through hole or the like provided with a conductor inside thereof (for example, a metal-plated through hole) in the dielectric substrate111. However, formation of such a through hole increases the manufacturing cost of the microstrip antenna1.

The transmission device100to which the exemplary embodiment is applied operates without connecting (even without contact) the ground conductor113of the transmission substrate110to the outer conductor123of the connector120(seeFIG.2Bdescribed later). In other words, the transmission device100to which the exemplary embodiment is applied does not require a through hole to be provided.

The First Exemplary Embodiment

FIGS.2A to2Cillustrate the transmission device100to which the first exemplary embodiment is applied.FIG.2Ais a perspective view in a state where the transmission substrate110and the connector120are in close proximity,FIG.2Bis a perspective view of the connector120, andFIG.2Cis a perspective view in a state where the connector120is mounted on the transmission substrate110. InFIGS.2A to2C, the x, y, and z directions are set as shown in the figures.

As shown inFIG.2A, the transmission substrate110includes the dielectric substrate111, the feeding line112, the ground conductor113, and a capacitive coupling conductor114. The feeding line112and the capacitive coupling conductor114are provided on the front surface of the dielectric substrate111(a surface in the +x direction). The feeding line112and the capacitive coupling conductor114are configured by a conductor (such as a copper foil) provided on the front surface of the dielectric substrate111. The feeding line112and the capacitive coupling conductor114are not connected to each other.

A planar shape of the feeding line112(viewed from the +z direction) is a strip shape as described above. A width W of the feeding line112is determined by a relative permittivity of the dielectric substrate111or the like, and the width W is set to a characteristic impedance for a signal transmission. The characteristic impedance is, for example, 50Ω.

The capacitive coupling conductor114is a conductor whose planar shape is U-shaped. A shape of the capacitive coupling conductor114surrounding an outer edge thereof is square115(seeFIG.3B. Here, it is rectangular). A circular opening a is provided at a center portion of the capacitive coupling conductor114, and a gap β from the outer edge to the opening a is provided at upper side (in the +y direction). In other words, the shape of the capacitive coupling conductor114surrounding the outer edge thereof is square, and the capacitive coupling conductor114has U-shape whose upper side is opened. A lower end (an end in the −y direction) of the feeding line112is positioned at the gap β of the capacitive coupling conductor114. Furthermore, a part of the capacitive coupling conductor114is removed from the square115at a lower right (an end in the −y and +x directions) and a lower left (an end in the −y and −x directions). The shape of the capacitive coupling conductor114surrounding the outer edge thereof is not limited to a square, a circle to be described later, or a pentagon, but may be a shape in which a part is removed from these shapes or in which another shape is added to these shapes. The shape of the capacitive coupling conductor114surrounding the outer edge thereof is a shape that encloses (connects) along the outer edge of the capacitive coupling conductor114as if no gap is provided and further encloses to include a part that has been removed. By making the planar shape of the capacitive coupling conductor114U-shaped, the feeding line112and the capacitive coupling conductor114are configured by one layer of conductor.

The ground conductor113is provided on the entire back surface of the dielectric substrate111, though only sign thereof is indicated. Therefore, the feeding line112and the capacitive coupling conductor114face the ground conductor113across the dielectric substrate111.

The connector120is an SMPM, and includes an insulator121, an inner conductor122, and an outer conductor123as shown inFIG.2B. The inner conductor122is a conductor through which a signal passes, and is sometimes referred to as a core wire. The inner conductor122is bent in an L-shape. That is, the inner conductor122includes a portion that is perpendicular to the dielectric substrate111and a portion that is parallel to the dielectric substrate111. A top end of the portion of the inner conductor122that is parallel to the dielectric substrate111is connected to the feeding line112of the transmission substrate110.

The outer conductor123includes a mounting portion123athat is mounted on the transmission substrate110and a connecting portion123bthat is connected to the coaxial cable. The mounting portion123ahas a flat bottom surface123a1, which is a surface at the side of the transmission substrate110(in the −z direction). The bottom surface123a1of the mounting portion123aof the connector120is connected to the capacitive coupling conductor114of the transmission substrate110. The connecting portion123bmay be configured to be easily connected to a connector on a side of the coaxial cable by a push-on locking mechanism.

The insulator121is provided between the inner conductor122and the outer conductor123. The insulator121provides insulation against direct current between the inner conductor122and the outer conductor123. The inner conductor122and the outer conductor123are composed of copper or copper alloy. The insulator121is composed of a resin such as polytetrafluoroethylene which has low loss to a high frequency signal. The shape of the connector120(the insulator121, the inner conductor122, and the outer conductor123) shown inFIG.2Bis a specific example, thus it may be other shapes.

As shown inFIG.2C, the connector120is mounted on the dielectric substrate111. Connection between the inner conductor122and the feeding line112and connection between the outer conductor123and the capacitive coupling conductor114can be made by solder or the like. The inner conductor122of the connector120is referred to as Port1, and the upper end of the feeding line112(the end in the +y direction) is referred to as Port2.

FIGS.3A to3Cillustrate the transmission device100to which the first exemplary embodiment is applied.FIG.3Ais a plan view,FIG.3Bis a side view, andFIG.3Cshows parameters of Example 1 used in a simulation. InFIG.3A, the right direction on the paper is the x direction, the upper direction on the paper is the y direction, and the front surface direction on the paper is the z direction. InFIG.3B, the right direction on the paper is the z direction, the upper direction on the paper is the y direction, and the back surface direction on the paper is the z direction. The connector120is a male type.

The plan view ofFIG.3Ais seen from a side of the connector120mounted on the transmission substrate110. The connector120is provided to overlap the feeding line112and the capacitive coupling conductor114on the transmission substrate110. InFIG.3A, the feeding line112and the capacitive coupling conductor114are shown with thick lines, and the connector120is shown with thin lines. The capacitive coupling conductor114which is hidden due to the connector120is shown with a dashed line. Here, the center of a portion of the inner conductor122of the connector120that is perpendicular to the dielectric substrate111, namely, the center of the inner conductor122on a side to which the coaxial cable is connected is referred to as a center O of the connector120. Then, a dimension from the center O of the connector120to an end of the capacitive coupling conductor114in the +x direction is referred to as Rx+, that to an end of the capacitive coupling conductor114in the −x direction is referred to as Rx−, that to an end of the capacitive coupling conductor114in the +y direction is referred to as Ry+, and that to an end of the capacitive coupling conductor114in the −y direction is referred to as Ry−.

The side view ofFIG.3Bshows the transmission device100shown inFIG.3Aseen from the −x direction side. As described above, the transmission substrate110includes the dielectric substrate111, the feeding line112and the capacitive coupling conductor114that are provided on the front surface of the dielectric substrate111(the surface in the +z direction), and the ground conductor113provided on the back surface of the dielectric substrate111(the surface in the −z direction). The mounting portion123aof the outer conductor123of the connector120is connected to the capacitive coupling conductor114, and the inner conductor122of the connector120is connected to the feeding line112. InFIG.3B, a portion of the inner conductor122hidden due to the outer conductor123of the connector120is shown with a dashed line.

As can be seen fromFIG.3B, the outer conductor123of the connector120and the ground conductor113of the transmission substrate110face each other via the dielectric substrate111. There is no DC connection between the outer conductor123of the connector120and the ground conductor113of the transmission substrate110. In other words, the outer conductor123of the connector120and the ground conductor113of the transmission substrate110are capacitively coupled via the capacitive coupling conductor114. It is possible to increase the coupling capacitance by facing the capacitive coupling conductor114and the ground conductor113each other.

The shape of the top end of the feeding line112(the portion connected to the inner conductor122of the connector120) is defined to facilitate connection with the inner conductor122of the connector120. Area of the capacitive coupling conductor114is set according to the wavelength of the signal, the amount of capacitive coupling, as well as the shape of the bottom123a1of the mounting portion123ain the outer conductor123of the connector120.

FIG.3Cshows dimensions of parameters of the capacitive coupling conductor114when matched in 28 GHZ band. The relative permittivity εr of the dielectric substrate111is 2.19 and thickness t of the dielectric substrate111is 0.127 mm. 28 GHz is a frequency in free space. Effective wavelength λg in the dielectric substrate111can be obtained by λ/sqrt(εr) based on the wavelength A in free space and the relative permittivity εr of the dielectric substrate111. In the case of 28 GHZ, the effective wavelength λg is 7.24 mm. Here, a characteristic impedance of the feeding line112is 50Ω, and a width W thereof is 0.37 mm. When the dimensions of the parameters of the capacitive coupling conductor114(Rx+, Rx−, Ry+, Ry−) are set as shown inFIG.3C, values of the ratio between the dimensions of the (Rx+, Rx−, Ry+, Ry−) with the effective wavelength λg (dimension/λg) is set to be more than ¼ λg (0.25 λg) and less than ½ λg (0.5 λg). The above transmission device100is represented as Example 1. InFIG.3C, Rx+ and Rx− are set to be the same value because the transmission device100is symmetrical in the left-right direction (±x direction) as shown inFIG.3A, but the values of Rx+ and Rx− need not be the same.

FIGS.4A and4Bshow S-parameters of Example 1 and comparative example obtained by the simulation.FIG.4Ashows S11andFIG.4Bshows S21. S11is a reflection characteristic at Port1shown inFIG.2C, and S21is a transmission characteristic from Port1to Port2shown inFIG.2C. InFIG.4A, the horizontal axis shows frequency [GHz] and the vertical axis shows S11[dB]. InFIG.4B, the horizontal axis shows frequency [GHz] and the vertical axis shows S21[dB]. InFIGS.4A and4B, as a comparative example, S11and S12are shown with dashed lines in a case where a transmission substrate with DC connection between the outer conductor123of the connector120and the ground conductor113of the dielectric substrate111is used.

As shown inFIG.4A, S11in Example 1 is equal to or less than −20 dB in the frequency range of 27 GHz to 30 GHz. Moreover, S11of Example 1 is smaller than S11of the comparative example. As can be seen from S21shown in FIG.4B, Example 1 has less loss in the frequency range of 27 GHZ to 30 GHz similar to the comparative example. In the transmission device100of Example 1, the outer conductor123of the connector120is capacitively coupled with the ground conductor113of the transmission substrate110via the capacitive coupling conductor114and there is no DC connection. However, the transmission characteristics of the transmission device100of Example 1 (S11and S21) have a small difference (equivalent) compared with the transmission device in which the outer conductor123of the connector120is connected in DC manner with the ground conductor113of the transmission substrate110. In other words, in the transmission device100of Example 1, by providing the capacitive coupling conductor114to capacitively couple the outer conductor123of the connector120with the ground conductor113of the transmission substrate110, it is not required to provide a through hole in the dielectric substrate111to connect the outer conductor123of the connector120in a DC manner with the ground conductor113of the transmission substrate110. Therefore, the manufacturing cost of the transmission device100is suppressed.

In the above, it has been explained that the dimensions from the center O of the connector120to the outer edge of the capacitive coupling conductor114(Rx+, Rx−, Ry+, Ry−) are more than ¼ and less than ½ of the effective wavelength λg. This is because, when the dimensions from the center O of the connector120to the outer edge of the capacitive coupling conductor114(Rx+, Rx−, Ry+, Ry−) are equal to or less than ¼ of the effective wavelength λg, the amount of capacitive coupling between the outer conductor123of the connector120and the ground conductor113of the transmission substrate110becomes small, thus it is difficult to maintain the outer conductor123of the connector120at the ground potential. On the other hand, when the dimensions from the center O of the connector120to the outer edge of the capacitive coupling conductor114(Rx+, Rx−, Ry+, Ry−) are ½ of the effective wavelength λg, excitation occurs and radio waves are radiated (becoming an antenna). Therefore, it is preferable that the dimensions from the center O of the connector120to the outer edge of the capacitive coupling conductor114(Rx+, Rx−, Ry+, Ry−) are set to be more than ¼ and less than ½ of the effective wavelength λg. When the dimensions from the center O of the connector120to the outer edge of the capacitive coupling conductor114are 2.3 mm (in the case of Rx+ and Rx−), the frequency corresponding to ¼ λg is about 16 GHz and the frequency corresponding to ½ λg is about 32 GHz. When the dimension from the center O of the connector120to the outer edge of the capacitive coupling conductor114is 2.6 mm (in the case of Ry+), the frequency corresponding to ¼ λg is about 20 GHz and the frequency corresponding to ½ λg is about 39 GHz. When the dimension from the center O of the connector120to the outer edge of the capacitive coupling conductor114is 3.0 mm (in the case of Ry−), the frequency corresponding to ¼ λg is about 17 GHz and the frequency corresponding to ½ λg is about 33 GHZ. Therefore, as shown in Example 1 ofFIGS.4A and4B, in the frequency range of 27 GHz to 30 GHZ, the transmission characteristics (S11, S21) have a small difference (equivalent) compared with the transmission device in which the outer conductor123of the connector120is connected in DC manner with the ground conductor113of the transmission substrate110. In this way, the shape of the capacitive coupling conductor114can be set based on the effective wavelength λg as in Example 1.

As will be described later, when n is an integer equal to or greater than 2, the difference will be small (equivalent) compared with the transmission device in which the outer conductor123of the connector120is connected in DC manner with the ground conductor113of the transmission substrate110, except for the frequency that is n×½ λg.

Next, the thickness t of the dielectric substrate111is described.

FIG.5shows parameters of Examples 1 and 2 with different thicknesses t of the dielectric substrates111. Example 1 is a case where the thickness t of the dielectric substrate111is 0.127 mm, and Example 2 is a case where the thickness t of the dielectric substrate111is 0.254 mm. Example 1 is the Example 1 shown inFIGS.3A to4B. In Example 2, the dimensions of the parameters of the capacitive coupling conductor (Rx+, Rx−, Ry+, Ry−) were adjusted to match in the 28 GHz band. In Example 2, the width W of the feeding line112is 0.6 mm to set the characteristic impedance to 50Ω because the dielectric substrate111is larger compared with Example 1.

FIGS.6A and6Bshow S-parameters of Example 1 and Example 2 obtained by the simulation.FIG.6Ashows S11andFIG.6Bshows S21. The horizontal axis and the vertical axis inFIGS.6A and6Bare the same as those inFIGS.4A and4B. Example 1 shown inFIGS.6A and6Bis the same as that shown inFIGS.4A and4B.

As shown inFIG.6A, in Example 2 where the thickness t of the dielectric substrate111is twice to be 0.254 mm, S11is smaller compared with Example 1 where the thickness t of the dielectric substrate111is 0.127 mm. On the other hand, as shown inFIG.6B, the pass characteristic in Example 2 is slightly lower compared with Example 1, thus it can be seen that the radiation loss increases. However, the difference in transmission characteristics (S11and S21) between Example 1 and Example 2 is small, and equivalent characteristics can be obtained. In other words, even if the thickness t of the dielectric substrate111is changed, equivalent characteristics can be obtained by adjusting the shape of the capacitive coupling conductor114.

The Second Exemplary Embodiment

In the transmission device100to which the first exemplary embodiment is applied, the planar shape of the capacitive coupling conductor114is U-shaped, and the shape surrounding the outer edge is the square115. In the transmission device100′ to which the second exemplary embodiment is applied, the planar shape of the capacitive coupling conductor114′ is U-shaped, however, the shape surrounding the outer edge is circular115′.

FIGS.7A and7Billustrate the transmission device100′ to which the second exemplary embodiment is applied.FIG.7Ais a plan view, andFIG.7Bshows parameters of Example 3 used in the simulation. The x, y, and z directions shown inFIG.7Aare the same as those inFIG.4A.

As shown inFIG.7A, the shape of the capacitive coupling conductor114′ surrounding the outer edge is circular115′ with a radius R. The capacitive coupling conductor114′ includes a circular opening α at a center portion and a gap β from the outer edge (circular115′) to the opening α. The other configurations are similar to those of the transmission device100described inFIGS.4A and4B. Therefore, the same signs are used and explanations will be omitted.

The parameter of the capacitive coupling conductor114′ shown inFIG.7Bis the radius R of the circular115′, which is the dimension from the center of the connector120to the outer edge of the capacitive coupling conductor114′. The relative permittivity εr of the dielectric substrate111is 2.19. Therefore, the effective wavelength λg is 7.24 mm. The thickness t of the dielectric substrate111is 0.127 mm as in Example 1. Therefore, the width W of the feeding line112is 0.37 mm as in Example 1. The radius R is set to 2.9 mm, which is considered to have good characteristics at 28.5 GHz. Even in this case, the value of the ratio (R/λg) between the dimension from the center O of the connector120to the edge of the capacitive coupling conductor114′ (radius R) with the effective wavelength λg is 0.4, which is more than ¼ λg and less than ½ λg.

FIGS.8A and8Bshow S-parameters of Example 3 obtained by the simulation.FIG.8Ashows S11andFIG.8Bshows S21. The horizontal axis and the vertical axis inFIGS.8A and8Bare the same as inFIGS.4A and4B. The relative permittivity εr of the dielectric substrate111is 2.19.

As shown inFIG.8A, S11of Example 3 is small near 29 GHz as in Example 1 shown inFIG.4A, on the other hand, S11of Example 3 is large at frequencies lower than 29 GHz and higher than 29 GHz. This is considered that, in addition to the fact that the radius R is set to a value that is considered to have good characteristics at 28.5 GHZ, is due to the mismatch that occurs between the transmission mode of the coaxial cable and the transmission mode of the transmission substrate110constituting the microstrip line. For this reason, the shape surrounding the outer edge of the capacitive coupling conductor114is preferably the square115of Example 1.

As shown inFIG.8B, S21in Example 3 significantly decreases near 34.7 GHZ. This is due to the fact that the frequency corresponding to ½ λg is about 35 GHz at a dimension of 2.9 mm (radius R) from the center of the connector120to the outer edge of the capacitive coupling conductor114′. On the other hand, at a dimension of 2.9 mm (radius R) from the center of the connector120to the outer edge of the capacitive coupling conductor114′, the frequency corresponding to ¼ λg is about 17 GHZ. Thus, the transmission device100′ operates in the frequency band more than 17 GHZ and less than 35 GHZ. As described above, except for the vicinity of 35 GHZ, the transmission device100′ operates in an even higher frequency band.

Third Exemplary Embodiment

In the transmission device100to which the first exemplary embodiment is applied, the planar shape of the capacitive coupling conductor114is U-shaped, and the shape surrounding the outer edge is the square115. In a transmission device100″ to which the third exemplary embodiment is applied, the planar shape of the capacitive coupling conductor114″ is U-shaped, however, the shape surrounding the outer edge is a pentagon (here, a regular pentagon)115″.

FIGS.9A and9Billustrate the transmission device100″ to which the third exemplary embodiment is applied.FIG.9Ais a plan view, andFIG.9Bshows parameters of Example 4 used in the simulation. The x, y, and z directions shown inFIG.9Aare the same as inFIG.4A.

As shown inFIG.9A, the shape surrounding the outer edge of the capacitive coupling conductor114″ is the pentagon115″. The dimension from the center of the connector120to an apex of the pentagon115″ is R max. The capacitive coupling conductor114″ includes a circular opening α at a center portion and a gap β from the outer edge (pentagon115″) to the opening α. The gap β is provided in one side of the pentagon115″. The other configurations are similar to those of the transmission device100described inFIGS.4A and4B. Therefore, the same signs are used and explanations will be omitted.

The parameter of the capacitive coupling conductor114″ shown inFIG.9Bis R max, which is the dimension from the center of the connector120to the outer edge of the capacitive coupling conductor114″ and is the dimension from the center of the pentagon115″ to the apex thereof. The relative permittivity εr of the dielectric substrate111is 2.19. Therefore, the effective wavelength λg is 7.24 mm. The thickness t of the dielectric substrate111is 0.127 mm as in Example 1. Therefore, the width W of the feeding line112is 0.37 mm as in Example 1. The R max is set to 3.2 mm, which is considered to have good characteristics at 28.5 GHZ. Even in this case, the value of the ratio (R max/λg) between the maximum dimension (R max) from the center O of the connector120(the center of the pentagon115″) to the edge side of the capacitive coupling conductor114″ with the effective wavelength λg is 0.44, which is more than ¼ λg and less than ½λg.

FIGS.10A and10Bshow S-parameters of Example 4 obtained by the simulation.FIG.10Ashows S11andFIG.10Bshows S21. The horizontal axis and the vertical axis inFIGS.10A and10Bare the same as inFIGS.4A and4B. The relative permittivity εr of the dielectric substrate111is 2.19.

As shown inFIG.10A, S11of Example 4 is small near 29 GHz as in Example 1 shown inFIG.4A, on the other hand, S11of Example 4 is large at frequencies lower than 29 GHz and higher than 29 GHz. Note that S11is again small near 34.4 GHz.

As shown inFIG.10B, in Example 4, S21significantly decreases near 33.5 GHZ. At the dimension of R max (3.2 mm) from the center to the apex of pentagon115″, the frequency corresponding to ½ λg is about 32 GHz. However, at 32 GHZ, there is little decrease in S21. On the other hand, at a dimension of R min (2.6 mm) from the center to the side of pentagon115″, the frequency corresponding to ½ λg is about 39 GHz. The frequency of 33.5 GHZ at which S21decreases lies between these frequencies.

In a case where the shape surrounding the outer edge of the capacitive coupling conductor114′ shown in Example 3 is circular115′, the dimension from the center of the connector120to the outer edge of the capacitive coupling conductor114′ does not change. Therefore, the frequency corresponding to ½ λg matches the calculated frequency. However, in a case where the shape surrounding the outer edge of the capacitive coupling conductor114″ is the pentagon115″, the dimension from the center of the connector120to the outer edge of the capacitive coupling conductor114″ changes. R max is the maximum dimension from the center to the outer edge of the pentagon115″, and R min is the minimum dimension from the center to the outer edge of the pentagon115″. The larger the dimension is, the lower the frequency corresponding to ½ λg is, while the smaller the dimension is, the higher the frequency corresponding to ½ λg is. Therefore, in a case where the shape surrounding the outer edge of the capacitive coupling conductor114″ is the pentagon115″, the frequency at which S21decreases is determined between the maximum dimension (R max) and the minimum dimension (R min) from the center of the connector120to the outer edge of the capacitive coupling conductor114″. Therefore, in order to suppress the decrease in S21in the frequency band, it is preferable to use, as the upper limit, the frequency where the maximum dimension (R max) from the center of the connector120to the outer edge of the capacitive coupling conductor114″ corresponds to ½ λg. Moreover, it is preferable to use, as the lower limit, the frequency where the minimum dimension (R min) from the center of the connector120to the outer edge of the capacitive coupling conductor114″ corresponds to ¼λg. In this way, the decrease in S21is suppressed between the frequencies of the lower limit and the upper limit. The shape of the capacitive coupling conductor can be set based on the desired frequency band. If the maximum dimension from the center of the connector120to the outer edge of the capacitive coupling conductor114″ is the same as the minimum dimension from the center of the connector120to the outer edge of the capacitive coupling conductor114″, it is sufficient that the maximum dimension and the minimum dimension are the same.

As shown inFIG.10B, S21increases again above 33.5 GHZ, and as shown inFIG.10A, S11also decreases. Therefore, when n is an integer equal to or greater than 2, the transmission device operates as a transmission device with a wider frequency band, except for the frequency at which n×¼ λg. Therefore, the shape of the capacitive coupling conductor114″ can be set according to the frequency band.

In the first, second, and third exemplary embodiments, the capacitive coupling conductors114,114′ and114″ have been described. The capacitive coupling conductors114,114′ and114″ constitute a capacitance (capacitor) with the ground conductor113. Therefore, the area of the capacitive coupling conductors114,114′ and114″ depends on the coupling capacitance between the outer conductor123of the connector120and the ground conductor113of the transmission substrate110. On the other hand, the dimension from the center of the connector120to the edges of the capacitive coupling conductors114,114′ and114″ affects the frequency of the signal. Therefore, the shape of the capacitive coupling conductors114,114′ and114″ should be set according to the coupling capacitance between the outer conductor123of the connector120and the ground conductor113of the transmission substrate110and according to the frequency of the signal to be transmitted. In this way, it is possible to suppress the manufacturing cost of the transmission devices100,100′, and100″ because it is not necessary to provide through holes or the like in the dielectric substrate111.

The shapes surrounding the outer edges of the capacitive coupling conductors114,114′ and114″ described in the first, second, and third exemplary embodiments are square, circular, and pentagon (regular pentagon). The shape surrounding the outer edge of the capacitive coupling conductors can be polygonal (including quadrilateral and pentagonal), circular, oval or the like. As in the capacitive coupling conductor114shown in the first exemplary embodiment, the shape of the capacitive coupling conductors may be a shape in which a part is removed therefrom or in which another shape is added thereto. In the microstrip antenna1shown inFIG.1A, the pitch of the radiating element300in the left-right direction (±x direction) is determined based on the wavelength of the radio waves transmitted and received by the radiating element300. As the wavelength of the radio wave becomes shorter, the pitch of the radiating element300in the left-right direction (±x direction) also becomes shorter. Therefore, the shape surrounding the edges of the capacitive coupling conductors should be narrower in the left-right (±x) direction, such as a square or oval shape. Thus, the shape of the capacitive coupling conductor114can be adapted to the purpose.

The first to third exemplary embodiments have been described above, however, various variations are allowed as long as not violating the intent of the present invention.

REFERENCE SIGNS LIST