Linearly polarized antenna and radar apparatus using the same

A linearly polarized antenna includes a dielectric substrate, a ground conductor which is overlapped on one surface of the dielectric substrate, an antenna element made of linearly polarized, which is formed on an opposite surface of the dielectric substrate, a plurality of metal posts in which one end side of each of the plurality of metal posts is connected to the ground conductor, the plurality of metal posts piercing through the dielectric substrate along a thickness direction thereof, another end side of each of the plurality of metal posts being extended to the opposite surface of the dielectric substrate, the plurality of metal posts being provided at predetermined intervals to form a cavity so as to surround the antenna element, and a conducting arm which short-circuits the other end of the plurality of metal posts along a line direction of the plurality of metal posts on the opposite surface side of the dielectric substrate, the conducting arm being provided while extended by a predetermined distance toward a direction of the antenna element, the conducting arm having a triangular portion.

This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP2005/020858 filed Nov. 14, 2005.

TECHNICAL FIELD

The present invention relates to a linearly polarized antenna in which a technique for realizing high performance, high productivity, and cost reduction is adopted and a radar apparatus using the linearly polarized antenna, and particularly to a linearly polarized antenna suitable to a UWB (Ultra-wideband) radar which will be used as an automotive radar in the future and a radar apparatus using the linearly polarized antenna.

BACKGROUND ART

It has been mainly proposed that UWB in which a submillimeter wave band ranging from 22 to 29 GHz is used is utilized as a vehicle-mounted or portable short-range radar (SRR).

It is necessary that an antenna of the radar apparatus used in the UWB have a broadband radiation characteristic, and that the antenna have a compact and thin type planar structure considering the fact that the antenna is placed in a gap between an automobile body and a bumper when mounted on the vehicle.

It is also necessary that the antenna make an exploration with a weak radio wave defined by the UWB, and the low-loss and high-gain antenna is required to suppress useless power consumption such that the antenna can be driven by a battery. Therefore, it is necessary that the arrayed antenna can easily be achieved.

For the purpose of the cost reduction, in the antenna, desirably a feed unit of an antenna element can be produced by a pattern printing technique.

As described above, the frequency band of 22 to 29 GHz is used for the UWB radar. However, the frequency band of 22 to 29 GHz includes an RR radio-wave emission prohibited band (23.6 to 24.0 GHz) for protecting a passive sensor of radio astronomy or earth exploration satellite service (EESS).

In 2002, in Non-Patent Document 1, FCC (Federal Communications Commission of USA) discloses a rule in which average power density is not more than −41.3 dBm and peak power density is set to 0 dBm/50 MHz in the frequency band of 22 to 29 GHz.

The rule also stipulates that an elevation-angle side lobe is decreased from −25 dB to −35 dB every few years in order to suppress radio interference to EESS.

Non-Patent Document 1: FCC 02-48 New Part 15 Rules, FIRST REPORT AND ORDER

However, in order to realize the decrease in elevation-angle side lobe, a dimension is increased in a perpendicular direction of the antenna used in the UWB radar, and it is envisioned that the antenna is hardly mounted in a general passenger car.

Therefore, in 2004, FCC adds a revised rule which is a method independent of the elevation-angle side lobe of the antenna as described in Non-Patent Document 2. In the revised rule, radiation power density of the RR radio-wave emission prohibited band is set to −61.3 dBm/MHz which is smaller than ever before by 20 dB.

Non-Patent Document 2: “Second Report and Order and Second Memorandum Opinion and Order” FCC 04-285, Dec. 16, 2004

A method of turning on and off a continuous wave (CW) from a continuous oscillator using a semiconductor switch is adopted in the conventional UWB radar.

In the method, a large residual carrier is generated due to incompleteness of switch isolation. Therefore, as shown by a broken line ofFIG. 18, the residual carrier is evacuated to an SRD (Short Range Device) band ranging from 24.05 to 24.25 GHz which is allocated for a Doppler radar.

However, because the SRD band is extremely close to the RR radio-wave emission prohibited band, there is a serious problem that the interference with EESS and the like cannot be avoided.

In order to solve the problem, there has been proposed a method in which a burst oscillator shown in Non-Patent Document 3 is used as the UWB radar.

The burst oscillator oscillates only when a pulse is on whereas the burst oscillator stops the oscillation when a pulse is off. Therefore, a residual carrier is not generated when the burst oscillator is used in the UWB radar.

Because any spectrum arrangement can be achieved, the band shown by a solid line ofFIG. 18can be used for the UWB radar, and as a result, the radiation power density can be suppressed to a sufficiently low level in the RR radio-wave emission prohibited band.

However, it is not easy to make the radiation power density 20 dB or more lower than a spectral peak only using the burst oscillator.

In this case, when the antenna has a characteristic in which the gain has a steep decline (notch) in the RR radio-wave emission prohibited band, the UWB radar which satisfies the new FCC rule can be realized by use of a combination of the antenna and the burst oscillator.

The invention is intended to provide an antenna suitable to the UWB radar which has the gain notch in the RR radio-wave emission prohibited band.

First of all, it is necessary that a broadband thin type planar antenna be realized as the antenna satisfying the various requirements.

As the thin type planar antenna, there is well known a so-called patch antenna having a configuration in which a rectangular or circular plate-like antenna element is formed on a dielectric substrate by patterning.

However, generally the patch antenna has a narrow band. In order to broaden the band, it is necessary to use a thick substrate having a low dielectric constant.

The low-loss substrate is required in order to use the antenna in the submillimeter wave band, and Teflon (registered trademark) is well known as such substrates.

However, because Teflon has difficulty in bonding a metal film, there is a problem that it is difficult to produce the antenna, resulting in cost increase.

Therefore, it is considered that a circularly polarized wave or a linearly polarized wave is used in the broadband element antenna necessary for UWB. In the case of the circularly polarized wave, there is an antenna such as a spiral antenna having the good characteristic.

However, the UWB antenna in which the linearly polarized wave is used is necessary because the circularly polarized wave cannot be used in the case of the vehicle-mounted short-range radar including a communication function. The realization of the short-range radar with the communication function is recently being studied.

In the case of the linearly polarized wave, there is a problem that it is not easy to obtain the broadband element antenna.

There is known a dipole antenna called bow-tie antenna as an element antenna of the relatively broadband linearly polarized wave. The dipole antenna is formed of a pair of triangles.

However, in the case where the bow-tie antenna is used as the array antenna, disturbance of the directivity is easily generated due to mutual connection between antennas.

A method of increasing the substrate thickness to about a quarter of a propagation wavelength is adopted in order to broaden the band in the planar antenna in which the dielectric substrate is used, and this method is effective in the case where the antenna is used as a single element.

However, in the array antenna in which the plural elements are arrayed, when the dielectric substrate is thickened, a surface wave propagating along the dielectric substrate surface is excited, which results in a problem that the elements are affected by the surface wave to hardly obtain the desired characteristic.

DISCLOSURE OF INVENTION

An object of the invention is to provide a linearly polarized antenna and a radar apparatus using the same. In the linearly polarized antenna, the influence of the surface wave is suppressed to obtain the good radiation characteristic in the broadband, the radiation is suppressed in the RR radio-wave emission prohibited band, and the high productivity and cost reduction can be realized.

In order to achieve the above object, a first aspect of the present invention provides a linearly polarized antenna comprising:

a dielectric substrate (21,21′,21″);

a ground conductor (22,22′) which is overlapped on one surface of the dielectric substrate;

an antenna element (23,23′) made of linearly polarized, which is formed on an opposite surface of the dielectric substrate;

a plurality of metal posts (30) in which one end side of each of the plurality of metal posts is connected to the ground conductor, and pierces through the dielectric substrate along a thickness direction thereof, another end side of each of the plurality of metal posts being extended to the opposite surface of the dielectric substrate, the plurality of metal posts being provided at predetermined intervals to form a cavity so as to surround the antenna element; and

a conducting rim (32,32′) which short-circuits the other end side of each of the plurality of metal posts along a line direction of the plurality of metal posts on the opposite surface side of the dielectric substrate, the conducting rim being provided while extended by a predetermined distance toward a direction of the antenna element.

In order to achieve the above object, a second aspect of the present invention provides the linearly polarized antenna according to the first aspect, wherein the antenna element is formed by a dipole antenna element having a pair of input terminals (25a,25b),

the linearly polarized antenna further comprises a feed pin (25) in which one end side is connected to one of the pair of input terminals of the dipole antenna element while another end side is provided to pierce through the dielectric substrate and the ground conductor, and

another of the pair of input terminals of the dipole antenna element pierces through the dielectric substrate to short-circuit the ground conductor.

In order to achieve the above object, a third aspect of the present invention provides the linearly polarized antenna according to the first aspect, wherein the conducting rim (32,32′) has at least a pair of uneven-width portions which are across the antenna element from each other.

In order to achieve the above object, a fourth aspect of the present invention provides the linearly polarized antenna according to the third aspect, wherein the pair of uneven-width portions is a pair of triangular portions.

In order to achieve the above object, a fifth aspect of the present invention provides the linearly polarized antenna according to the third aspect, wherein a plurality of sets of the antenna element formed on the dielectric substrate and a plurality of sets of the feed pin in which one end of the feed pin is connected to one of the pair of input terminals of the antenna element are provided,

the plurality of metal posts constituting the cavity and the conducting rim are formed in a lattice shape so as to surround the plurality of sets of the antenna element, and

the linearly polarized antenna further comprises a feed unit (40) which is provided on the side of the ground conductor to distribute and feed an excitation signal to the plurality of sets of the antenna element through the plurality of sets of the feed pin.

In order to achieve the above object, a sixth aspect of the present invention provides the linearly polarized antenna according to the fifth aspect, wherein the feed unit is formed by a feeding dielectric substrate (41) and a microstrip feed line (42), the feeding dielectric substrate being provided on the side opposite the dielectric substrate across the ground conductor, the microstrip feed line being formed on a surface of the feeding dielectric substrate.

In order to achieve the above object, a seventh aspect of the present invention provides the linearly polarized antenna according to the second aspect, wherein the dipole antenna element is formed in a triangular shape having a predetermined base width WBand a predetermined height LB/2, and the dipole antenna element constitutes a bow-tie antenna while vertexes thereof are arranged so as to face each other.

In order to achieve the above object, an eighth aspect of the present invention provides the linearly polarized antenna according to the second aspect, wherein the dipole antenna element is formed in a deformed rhombic shape having a predetermined projection width WBand a predetermined height LB/2, and the dipole antenna element constitutes a bow-tie antenna while vertexes thereof are arranged so as to face each other.

In order to achieve the above object, a ninth aspect of the present invention provides the linearly polarized antenna according to the first aspect, wherein a first linearly polarized antenna element (23,23′) and a second linearly polarized antenna element (23,23′) are formed as the antenna element on the dielectric substrate (21″),

one end side of each of the plurality of metal posts (30) is connected to the ground conductor, and pierces through the dielectric substrate along a thickness direction thereof, another end side of each of the plurality of metal posts is extended to the opposite surface of the dielectric substrate, the plurality of metal posts are provided at predetermined intervals to form separated cavities such that the plurality of metal posts surround the first linearly polarized antenna element and the second linearly polarized antenna element while separating the first linearly polarized antenna element and the second linearly polarized antenna element, and

a first conducting rim (32) and a second conducting rim (32′) are provided as the conducting rim (32,32′) on the opposite surface of the dielectric substrate, the first conducting rim and the second conducting rim short-circuiting the other end side of each of the plurality of metal posts along a line direction of the plurality of metal posts, the plurality of metal posts being provided at predetermined intervals so as to surround the first linearly polarized antenna element and the second linearly polarized antenna element while separating the first linearly polarized antenna element and the second linearly polarized antenna element, the first conducting rim and the second conducting rim being extended by a predetermined distance toward directions of the first linearly polarized antenna element and the second linearly polarized antenna element.

In order to achieve the above object, a tenth aspect of the present invention provides the linearly polarized antenna according to the ninth aspect, wherein one of the first linearly polarized antenna element and the second linearly polarized antenna element is applied as a transmitting antenna (51) of a radar apparatus (50) and another is applied as a receiving antenna (52) of the radar apparatus (50).

In order to achieve the above object, an eleventh aspect of the present invention provides the linearly polarized antenna according to any one of the first to tenth aspects, wherein a resonator is formed by the cavity and the conducting rim, structural parameters of the resonator and the antenna element are adjusted to set the resonator to a desired resonance frequency, and thereby a frequency characteristic is obtained such that a gain of the linearly polarized antenna is decreased in a predetermined range.

In order to achieve the above object, a twelfth aspect of the present invention provides the linearly polarized antenna according to the eleventh aspect, wherein the structural parameter includes at least one of a internal dimension Lw of the cavity, a rim width LRof the conducting rim, an overall length LBof the antenna element, and a horizontal width WBof the antenna element.

In order to achieve the above object, a thirteenth aspect of the present invention provides a radar apparatus (50) comprising:

a transmitting unit (54) which radiates a radar pulse to a space via a transmitting antenna (51);

a receiving unit (55) which receives the radar pulse wave reflected from an object existing in the space via a receiving antenna (52);

an analysis processing unit (56) which explores the object existing in the space based on a receiving output from the receiving unit; and

a control unit (53) which controls at least one of the transmitting unit and the receiving unit based on an output from the analysis processing unit,

wherein the transmitting antenna and the receiving antenna are respectively formed by first and second linearly polarized antenna elements (23,23′), and the first and second linearly polarized antenna elements (23,23′) respectively include:

a dielectric substrate (21,21′,21″);

a ground conductor (22,22′) which is overlapped on one surface of the dielectric substrate;

an antenna element (23,23′) made of linearly polarized, which is formed on the opposite surface of the dielectric substrate;

a plurality of metal posts (30) in which one end side of each of the plurality of metal posts is connected to the ground conductor, and pierces through the dielectric substrate along a thickness direction thereof, another end side of each of the plurality of metal posts being extended to the opposite surface of the dielectric substrate, the plurality of metal posts being provided at predetermined intervals to form a cavity so as to surround the antenna element; and

a conducting rim (32,32′) which short-circuits the other end side of each of the plurality of metal posts along a line direction of the plurality of metal posts on the opposite surface side of the dielectric substrate, the conducting rim being provided while extended by a predetermined distance in the direction of the antenna element,

the one end side of each of the plurality of metal posts (30) is connected to the ground conductor, and pierces through the dielectric substrate along a thickness direction thereof, the other end of each of the plurality of metal posts is extended to the opposite surface of the dielectric substrate, the plurality of metal posts are provided at predetermined intervals to form separated cavities such that the plurality of metal posts surround the first linearly polarized antenna element and the second linearly polarized antenna element while separating the first linearly polarized antenna element and the second linearly polarized antenna element, and

a first conducting rim (32) and a second conducting rim (32′) are provided as the conducting rim (32,32′) on the opposite surface of the dielectric substrate, the first conducting rim and the second conducting rim short-circuiting the other end side of each of the plurality of metal posts along a line direction of the plurality of metal posts, the plurality of metal posts being provided at predetermined intervals so as to surround the first linearly polarized antenna element and the second linearly polarized antenna element while separating the first linearly polarized antenna element and the second linearly polarized antenna element, the first conducting rim and the second conducting rim being extended by a predetermined distance toward directions of the first linearly polarized antenna element and the second linearly polarized antenna element.

In order to achieve the above object, a fourteenth aspect of the present invention provides the radar apparatus (50) according to the thirteenth aspect, wherein the antenna element is formed by a dipole antenna element having a pair of input terminals (25a,25b),

the linearly polarized antenna further comprises a feed pin (25) in which one end side is connected to one of the pair of input terminals of the dipole antenna element while another end side is provided to pierce through the dielectric substrate and the ground conductor, and

another of the pair of input terminals of the dipole antenna element pierces through the dielectric substrate to short-circuit the ground conductor.

In order to achieve the above object, a fifteenth aspect of the present invention provides the radar apparatus (50) according to the thirteenth aspect, wherein the conducting rim (32,32′) has at least a pair of uneven-width portions which are across the antenna element from each other.

In order to achieve the above object, a sixteenth aspect of the present invention provides the radar apparatus (50) according to the fifteenth aspect, wherein the pair of uneven-width portions is a pair of triangular portions.

In order to achieve the above object, a seventeenth aspect of the present invention provides the radar apparatus (50) according to the fourteenth aspect, wherein a plurality of sets of the antenna element formed on the dielectric substrate and a plurality of sets of the feed pin in which one end of the feed pin is connected to one of the pair of input terminals of the antenna element are provided,

the plurality of metal posts constituting the cavity and the conducting rim are formed in a lattice shape so as to surround the plurality of sets of the antenna element, and

the linearly polarized antenna further comprises a feed unit (40) which is provided on the side of the ground conductor to distribute and feed an excitation signal to the plurality of sets of the antenna element via the plurality of sets of the feed pin.

In order to achieve the above object, an eighteenth aspect of the present invention provides the radar apparatus (50) according to the seventeenth aspect, wherein the feed unit is formed by a feeding dielectric substrate (41) and a microstrip feed line (42), the feeding dielectric substrate being provided on the side opposite the dielectric substrate across the ground conductor, the microstrip feed line being formed on a surface of the feeding dielectric substrate.

In order to achieve the above object, a nineteenth aspect of the present invention provides the radar apparatus (50) according to the fourteenth aspect, wherein the dipole antenna element is formed in a triangular shape having a predetermined base width WBand a predetermined height LB/2, and the dipole antenna element constitutes a bow-tie antenna while vertexes thereof are arranged so as to face each other.

In order to achieve the above object, a twentieth aspect of the present invention provides the radar apparatus (50) according to the fourteenth aspect, wherein the dipole antenna element is formed in a deformed rhombic shape having a predetermined projection width WBand a predetermined height LB/2, and the dipole antenna element constitutes a bow-tie antenna while vertexes thereof are arranged so as to face each other.

In order to achieve the above object, a twenty-first aspect of the present invention provides the radar apparatus (50) according to any one of the thirteenth to twentieth aspects, wherein a resonator is formed by the cavity and the conducting rim, structural parameters of the resonator and the antenna element are adjusted to set the resonator to a desired resonance frequency, and thereby a frequency characteristic is obtained such that a gain of the linearly polarized antenna is decreased in a predetermined range.

In order to achieve the above object, a twenty-second aspect of the present invention provides the radar apparatus (50) according to the twenty-first aspect, wherein the structural parameter includes at least one of a internal dimension Lw of the cavity, a rim width LRof the conducting rim, an overall length LBof the antenna element, and a horizontal width WBof the antenna element.

In the linearly polarized antenna of the invention having the above configuration, the plurality of metal posts piercing through the dielectric substrate are arranged so as to surround the antenna element, and thereby the cavity structure is formed. Additionally, the one end of each of the plurality of metal posts is short-circuited along the line direction, and the conducting rim (rim/conducting rim) is provided while extended by the predetermined distance in the antenna element direction. Therefore, the generation of the surface wave can be suppressed and the antenna can be set to the desired radiation characteristic.

In the linearly polarized antenna of the invention, the frequency characteristic of the antenna gain can be set so as to have the steep decline (notch) in the RR radio-wave emission prohibited band by utilizing the resonance phenomenon of the cavity, which effectively decreases the radio interference with EESS or the radio astronomy service.

In the linearly polarized antenna of the invention, a fluctuation in characteristic caused by the influence of the surface wave between the antenna elements can be prevented even if the antenna is arrayed.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

FIGS. 1 to 5show a basic structure of a linearly polarized antenna20according to a first embodiment of the invention.

FIG. 1is a perspective view showing a configuration of the linearly polarized antenna according to the first embodiment of the invention.

FIG. 2is a front view showing the configuration of the linearly polarized antenna according to the first embodiment of the invention.

FIG. 3is a rear view showing the configuration of the linearly polarized antenna according to the first embodiment of the invention.

FIG. 4Ais an enlarged sectional view taken on a line4A-4A ofFIG. 2.

FIG. 4Bis an enlarged sectional view taken on a line4B-4B in a modification ofFIG. 2.

FIG. 5is an enlarged sectional view taken on a line5-5ofFIG. 2.

Basically, as shown inFIGS. 1 to 5, the linearly polarized antenna of the invention includes a dielectric substrate21, a ground conductor22, a linearly polarized antenna element23, a plurality of metal posts30, and a conducting rim32. The ground conductor22is overlapped on one surface side of the dielectric substrate21. The linearly polarized antenna element23is formed on the opposite surface of the dielectric substrate21. One end side of each of the plurality of metal posts30is connected to the ground conductor22, and pierces through the dielectric substrate21in a thickness direction thereof. Another end side of each of the plurality of metal posts30is extended to the opposite surface of the dielectric substrate21. The plurality of metal posts30are provided at predetermined intervals so as to surround the antenna element23, which constitutes a cavity. On the opposite surface of the dielectric substrate21, the other end side of each of the plurality of metal posts30is short-circuited along a line direction of the plurality of metal posts30. The conducting rim32is provided while extended by a predetermined distance in a direction of the antenna element23.

Specifically, the linearly polarized antenna20is a substrate made of a material having a low dielectric constant (around 3.5). For example, the linearly polarized antenna20includes the dielectric substrate21having a thickness of 1.2 mm, the ground conductor22provided on one surface side (rear surface inFIGS. 1 and 2) of the dielectric substrate21, a dipole antenna element23, one feed pin25, and one short pin26. The dipole antenna element23is formed by a pair of element antennas23aand23b. The pair of element antennas23aand23bexcites the cavity with a linearly polarized wave, and is formed on the opposite surface of the dielectric substrate21(front surface inFIGS. 1 and 2) by a pattern printing technique. The feed pin25and the short pin26feed a power to the antenna element23.

The feed pin25and the short pin26pierce through the dielectric substrate21in the thickness direction thereof, the feed pin25further pierces through a hole22aof the ground conductor22, and the short pin26is short-circuited to the ground conductor22.

Because the dipole antenna element23is an antenna of a balanced type element, balanced feed can be performed.

In such cases, instead of the one feed pin25and the one short pin26, two feed pins may be provided to pierce through two holes made in the ground conductor22.

However, frequently the power is fed to the antenna using a coaxial line or a microstrip line.

Because the coaxial line and the microstrip line are so-called unbalanced lines, it is necessary to insert a balun between the feed pin and the antenna when the power is fed to the antenna of the balanced element such as the dipole antenna element23.

However, when the broadband characteristic necessary to UWB is realized, it is impractical because the balun is significantly enlarged.

In the invention, in order to solve the problem, as described above, the power is fed to the element antenna23bof the pair of element antennas23aand23bconstituting the dipole antenna element23through the feed pin25using the coaxial cable, the coplanar line in which the ground conductor22is set to a ground line, or the later-mentioned microstrip line, and the other element antenna23ais short-circuited to the ground conductor22through the short pin26. Therefore, even if the feed line is substantially the unbalanced type, the power can be fed without using the balun.

Consequently, the radiowave of the linearly polarized wave can be radiated from the antenna element23.

The dielectric substrate21can be made of a material such as RO4003 (product of Rogers company) having the low-loss in the submillimeter wave band.

The dielectric substrate21can be made of a low-loss material whose dielectric constant ranges from about 2 to about 5, and examples of the material include a glass fabrics Teflon substrate and various thermoset resin substrates.

However, in the linearly polarized antenna having only the above structure, because the surface wave is excited along the surface of the dielectric substrate21as described above, the desired characteristic of the linearly polarized antenna is not obtained by the influence of the surface wave.

Therefore, in the linearly polarized antenna20of the first embodiment, as shown inFIGS. 4A and 5, the cavity structure is adopted in addition to the above structure. For example, a plurality of cylindrical metal posts30are provided at predetermined intervals so as to surround the antenna element23, which forms the cavity structure. One end side of each of the plurality of cylindrical metal posts30is connected to the ground conductor22, and pierces through the dielectric substrate21. Another end side of each of the plurality of cylindrical metal posts30is extended to the opposite surface of the dielectric substrate21.

Furthermore, in the linearly polarized antenna20of the first embodiment, a conducting rim32is provided on the opposite surface of the dielectric substrate21in addition to the cavity structure. The other end side of each of the plurality of metal posts30is sequentially short-circuited along the line direction by the conducting rim32, and the conducting rim32is extended by the predetermined distance toward the direction of the antenna element23from a connection point to each of the plurality of metal posts30.

In the linearly polarized antenna20of the first embodiment, the surface wave can be suppressed by a synergetic effect of the cavity structure and the conducting rim32.

As shown inFIG. 4B, the plurality of metal posts30can be realized by forming a plurality of holes301thereby piercing through the dielectric substrate21, and forming a plurality of hollow metal posts30′ thereby plating (through-hole plating) to inner walls of the plurality of holes301.

In this case, lower end portions of the plurality of hollow metal posts30′ formed by the through-hole plating are connected to the ground conductor22through lands302. The land302is formed on one end side of the dielectric substrate21by the pattern printing technique.

Structural parameters of each portion and simulation result obtained by changing the structural parameters for the characteristic of the linearly polarized antenna20will be described in order to explain the effect of suppressing the surface wave by the cavity structure and the conducting rim32.

A factor which becomes the structural parameter of each portion will be described.

The frequency of 26 GHz in UWB is used in the linearly polarized antenna20. As shown inFIG. 6, the dipole antenna element23includes a pair of input terminals25aand25b, and a triangular bow-tie antenna is used as the dipole antenna element23. The triangular bow-tie antenna has a horizontal width WBof about 1.8 mm and an overall length LBof about 3.5 mm.

In the following descriptions and embodiments, a triangular example is shown as the antenna element23which should be adopted as the linearly polarized antenna20.

As shown inFIG. 7, in place of the triangular shape, a deformed rhombic antenna element23can also be used as the dipole antenna element23which should be adopted as the linearly polarized antenna20. The deformed rhombic antenna element23includes the pair of input terminals25aand25b, and has a predetermined projection width WBand an overall length LB.

The dielectric substrate21has a square outer shape while a central hub of the antenna element23is centered on the square shape. As shown inFIG. 2, the square shape has a side of L (hereinafter referred to as outline length), and the cavity is also formed in the square shape having the same central hub.

As shown inFIGS. 4A and 4B, an internal dimension of the cavity is set to Lw, and a distance (hereinafter referred to as rim width) extended inward from a cavity inner wall of the conducting rim32is set to LR.

The diameter of each of the plurality of metal posts30forming the cavity is 0.3 mm, and the interval between the plurality of metal posts30is 0.9 mm.

FIG. 8shows radiation directivity in a perpendicular surface (yz-surface inFIGS. 1 and 2) of each of three types of antennas in which the bow-tie antenna is used.

InFIG. 8, the numeral F1designates the simulation result of the radiation directivity when the cavity by the plurality of metal posts30and the conducting rim32are not provided.

The numeral F2designates the radiation directivity when the cavity is provided by the plurality of metal posts30while the conducting rim32is not provided.

The numeral F3designates the radiation directivity when both the cavity by the plurality of metal posts30and the conducting rim32are provided.

A broad single-peaked characteristic which is symmetrical in relation to the direction of 0° is required for the radiation characteristic of the linearly polarized antenna.

As is clear fromFIG. 8, in the radiation directivity F1in which the cavity by the plurality of metal posts30and the conducting rim32are not provided, asymmetry becomes large in relation to the direction of 0°, and the directivity does not have the single-peaked characteristic.

As easily anticipated, this is attributed to the fact that the wave excited by the bow-tie antenna is diffused as the surface wave in the dielectric substrate21because the cavity by the plurality of metal posts30does not exist.

On the other hand, in the radiation directivity F2in which the cavity is provided by the plurality of metal posts30while the conducting rim32is not provided, because the cavity by the plurality of metal posts30exists, it is assumed that the antenna having the good characteristic is obtained. However, as shown inFIG. 8, actually the radiation directivity F2also has the asymmetry in relation to the direction of 0°.

This means that the surface wave cannot be sufficiently suppressed only using the cavity by the plurality of metal posts30.

On the other hand, in the radiation directivity F3in which both the cavity by the plurality of metal posts30and the conducting rim32are provided, symmetry is obtained in relation to the direction of 0°, and the directivity has the broad single-peaked characteristic.

This is because the surface wave transmitted to the outside of the cavity is suppressed with both the cavity by the plurality of metal posts30and the conducting rim32to generate the radio wave radiation only from an opening of the cavity, and it is clear that the large effect is obtained by providing the conducting rim32.

The rim width LRis determined by a simulation or an experiment in such a manner that, as described later, the notch is generated in the antenna gain in the RR radio-wave emission prohibited band while the surface wave is suppressed.

Typically, the rim width LRhas a value of 1.2 mm.

The rim width LR=1.2 mm corresponds substantially to a quarter of the wavelength of the surface wave.

That is, the portion having the rim width LR=1.2 mm forms a transmission path having a length of λg/4 (λg is a wavelength of waveguide) in which impedance becomes infinite for the surface wave when the post wall side is viewed from the front end side.

Accordingly, an electric current is not passed along the surface of the dielectric substrate21, and the excitation of the surface wave is suppressed to prevent the fluctuation in the radiation characteristic by the electric-current blocking action.

Therefore, the setting of the rim width LRmay be changed according to the frequency in the case where the linearly polarized antenna20is applied to frequency bands other than the above frequency band.

The linearly polarized antenna20of the first embodiment can be used in various communication systems in UWB.

Second Embodiment

The linearly polarized antenna20of the first embodiment may be arrayed in the case where the gain necessary for the UWB radar runs short or in the case where the beam needs to be narrowed.

FIGS. 9 to 11show a configuration of an arrayed linearly polarized antenna20′ which is a second embodiment of the linearly polarized antenna according to the invention.

FIG. 9is a front view showing a configuration of an array to which the linearly polarized antenna according to the second embodiment of the invention is applied.

FIG. 10is a side view showing the configuration of the array to which the linearly polarized antenna according to the second embodiment of the invention is applied.

FIG. 11is a rear view showing the array to which the linearly polarized antenna according to the second embodiment of the invention is applied.

In the linearly polarized antenna20′ according to the second embodiment, a plurality sets of the antenna element23of the first embodiment are arrayed in two rows and four columns on common longitudinally rectangular dielectric substrate21′ and ground conductor22′.

A feed unit40which distributes and feeds an excitation signal to the plurality sets of the antenna element23is formed on the side of the ground conductor22′ of the linearly polarized antenna20′.

Eight antenna elements23(1) to23(8) which are the triangular bow-tie antenna formed in the same way as the first embodiment are provided in the two rows and four columns on the surface of the dielectric substrate21′.

Similar to the first embodiment, each of the antenna elements23(1) to23(8) is surrounded by the cavity formed by arranging the plurality of metal posts30whose one end sides are connected to the ground conductor22′.

In the antenna elements23(1) to23(8), the plurality of metal posts30are coupled to one another along the line direction on the other side of each of the plurality of metal posts30by a conducting rim32′. The conducting rim32′ is extended by a predetermined distance (the rim width LR) toward the direction of the antenna element23from the connection point to each of the plurality of metal posts30.

That is, each of the antenna elements23(1) to23(8) is configured to suppress the generation of the surface wave.

In the case where the plurality of antenna elements23(1) to23(8) are arranged longitudinally and horizontally like the linearly polarized antenna20′, the cavity and conducting rim32′ which are provided between the adjacent antenna elements are commonly used, and the linearly polarized antenna20′ can be formed in a lattice shape as a whole.

However, the conducting rim32′ provided between the two adjacent antenna elements is formed so as to be extended by the predetermined distance (the rim width LR) toward the both antenna elements.

One end of each of feed pins25(1) to25(8) is connected to a feed point of each of the antenna elements23(1) to23(8). Each of the feed pins25(1) to25(8) pierces through the dielectric substrate21′ and passes through a hole22a′ of the ground conductor22′ in a non-conductive manner. Then, each of the feed pins25(1) to25(8) pierces through a feeding dielectric substrate41constituting the feed unit40and the other end side of each of the feed pins25(1) to25(8) is projected to the surface of the feeding dielectric substrate41.

As shown inFIG. 11, microstrip feed lines42(a) to42(h) and42(b′) to42(h′) are formed on the surface of the feeding dielectric substrate41while grounded to the ground conductor22′.

The feed lines42(a) to42(h) and42(b′) to42(h′) include two feed lines42band42b′, two lines42cand42d, and four feed lines42eto42h. The two feed lines42band42b′ are horizontally branched out from an input and output feed line42aconnected to a transmitting unit (not shown) or a receiving unit (not shown). The two lines42cand42dare vertically branched out from the line42bextended leftward. The four feed lines42eto42hare branched out from the two lines42cand42d.

InFIG. 11, the four feed lines42eto42hare connected to the feed pins25(1) to25(4) of the antenna elements23(1) to23(4) in the right row.

Substantially similar to the left-side line42b, the line42b′ branched out rightward from the input and output feed line42ahas vertically branched two feed lines42c′ and42d′ and four feed lines42e′ to42h′ branched out from the two lines42c′ and42d′.

InFIG. 9, the four feed lines42e′ to42h′ are connected to the feed pins25(5) to25(8) of the antenna elements23(5) to23(8) in the left row.

Because the line lengths to the feed pins25(1) to25(8) are equally set when viewed from the input and output feed line42a, the power is fed to the antenna element in the same phase, and a radiation beam is orientated toward the front of the antenna.

In the linearly polarized antenna20′ of the second embodiment having the above configuration, the generation of the surface wave is suppressed by the cavity and conducting rim32′ formed by the plurality of metal posts30in each antenna element23. Therefore, similar to the first embodiment, mutual connection between the elements is decreased to obtain the desired radiation characteristic which is the single-peaked directivity.

In the linearly polarized antenna20′ of the second embodiment, beam spread in a vertical plane can appropriately be narrowed because the antenna elements are longitudinally arrayed in four columns, and the radiation in the high-elevation-angle direction which becomes problematic can be suppressed even if the component of the RR radio-wave emission prohibited band in the UWB band is included. Therefore, the linearly polarized antenna20′ of the second embodiment also has the effect of reducing the interruption to the RR radio-wave emission prohibited band.

In the feed unit40of the arrayed linearly polarized antenna20′, the excitation signal is distributed and fed to each antenna element by the microstrip feed line42formed on the feeding dielectric substrate41. Alternatively, the feed unit can be formed by a coplanar line.

In this case, similarly there may be adopted either the method of forming the coplanar line type feed line on the surface of the feeding dielectric substrate41or the method of directly forming the coplanar line type feed line in the ground conductor22′.

Particularly, in the latter method, there is an advantage that the feeding dielectric substrate41can be omitted.

In the linearly polarized antenna of the invention, it can be thought that a resonator is formed by providing the cavity, formed by the plurality of metal posts30, and the conducting rim32in the dielectric substrate21and the resonator is excited by the linearly polarized antenna element23.

Because the resonator is formed in the linearly polarized antenna of the invention, a resonance frequency exists, and input impedance of the linearly polarized antenna is largely increased to eliminate the radiation in the resonance frequency.

In this case, the resonance frequency of the resonator is determined by the structural parameters of the resonator and the linearly polarized antenna element.

As described above, examples of the structural parameters include the number of turns of the element antenna, a basic length a0of the element, and a line width W in addition to the internal dimension Lw of the cavity and the rim width LR.

Accordingly, the steep decline (notch) is rapidly generated near the resonance frequency in the frequency characteristic of the antenna gain.

When the resonance frequency is matched with the RR radio-wave emission prohibited band (23.6 to 24.0 GHz), the antenna as transmitting antenna of the UWB radar can be used to largely reduce the interference with the earth exploration satellite and the like.

However, because the notch is generally the narrow band, in consideration of production error, it is important to sufficiently broaden the band of the notch in order to cover the RR radio-wave emission prohibited band.

Third Embodiment

A third embodiment of a linearly polarized antenna according to the invention in which a configuration to broaden the band of the notch is adopted will be described below.

FIGS. 12A to 12Care enlarged front views showing a configuration of a main part to which a linearly polarized antenna20according to the third embodiment of the invention is applied and configurations of two different modifications.

Each of the linearly polarized antenna20shown inFIGS. 12A,12B, and12C is characterized in that the width of a conducting rim32is unevenly formed.

The linearly polarized antenna20ofFIG. 12Ashows an example in the case where a wave shape is formed as any shape which can be taken to unevenly form the width of the conducting rim32.

The linearly polarized antenna20ofFIG. 12Bshows an example in the case where an arc is formed as any shape which can be taken to unevenly form the width of the conducting rim32.

The linearly polarized antenna20ofFIG. 12Cshows an example in the case where a triangle is formed as any shape which can be taken to unevenly form the width of the conducting rim32.

As shown inFIG. 2, in the case where the conducting rim32is formed in the square even width, a λ/4 transmission path having the infinite impedance is formed to extremely sharpen the resonance in the resonance frequency when viewed from the front end side to the post wall side. On the other hand, as shown inFIGS. 12A,12B, and12C, the resonance becomes duller by unevenly forming the width of the conducting rim32.

FIG. 13is a view explaining the effect in the case where the conducting rim32is formed in the triangular shape as shown inFIG. 12C. The conducting rim32shown inFIG. 12Chas the simplest configuration in the linearly polarized antennas20.

In this case, specifically h1is set to about 0.26 mm, and h2is set to about 1.26 mm inFIG. 12C.

InFIG. 13, a broken line indicates the frequency characteristic of the antenna gain in the case of the conducting rim32having the square even width whose rim width is LR=1.0 mm as shown inFIG. 2.

A solid line indicates the frequency characteristic of the antenna gain in the case of the conducting rim32having the triangular uneven width of h1=0.26 mm and h2=1.26 mm as shown inFIG. 12C.

As is clear fromFIG. 13, a frequency width at the position where the gain at 26 GHz is decreased by 10 dBi is about 260 MHz in the case of the square conducting rim32indicated by the broken line, whereas the frequency width is at least 500 MHz in the case of the triangular conducting rim32indicated by the solid line.

That is, because the RR radio-wave emission prohibited band has the width of 400 MHz, the RR radio-wave emission prohibited band having the width of 400 MHz is not sufficiently covered with the bandwidth of the notch in the case of the square conducting rim32shown by the broken line. On the other hand, the RR radio-wave emission prohibited band having the width of 400 MHz is sufficiently covered with the bandwidth of the notch in the case of the triangular conducting rim32shown by the solid line.

Fourth Embodiment

FIG. 14is a front view showing a configuration of a main part to which a linearly polarized antenna according to a fourth embodiment of the invention is applied.

That is, in the linearly polarized antenna to which the fourth embodiment is applied, as shown inFIG. 12C, the array antenna is formed with the antenna elements in which the conducting rims32are formed in the triangular shapes.

The configuration of the array antenna shown inFIG. 14is a 2×4 element array similar to that ofFIG. 9.

FIG. 15shows a frequency characteristic of an antenna gain of the array antenna shown inFIG. 14.

In the example, the gain is kept at 15 dBi in the range of 25 to 29 GHz, the steep notch where the gain is decreased by at least about 10 dBi from the peak level is generated in the range of 23.6 to 24.0 GHz, and the necessary bandwidth is obtained in the notch.

In the linearly polarized antenna of the invention, the RR radio-wave emission prohibited band can be covered with the frequency in which the notch is generated and the bandwidth of the notch by appropriately selecting one of the structural parameters of the resonator, the conducting rim, and the bow-tie antenna element.

Thus, in the linearly polarized antenna of the invention, the frequency in which the notch is generated can be matched with the RR radio-wave emission prohibited band by appropriately selecting one or both the structural parameters of the resonator and the antenna element.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably the antenna elements23and23′ are formed by the dipole antenna elements23and23′ having the pair of input terminals25aand25b, the feed pin25is further provided, one end side of the feed pin25is connected to one of the pair of input terminals25aand25bof the dipole antenna elements23and23′, the other side of the feed pin25pierces through the dielectric substrates21and21′ and the ground conductors22and22′, and the other of the pair of input terminals25aand25bof the dipole antenna elements23and23′ pierces through the dielectric substrates21and21′ and short-circuits the ground conductors22and22′.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably the conducting rims32and32′ have at least a pair of uneven-width portions, e.g., a pair of triangular portions which is located across the antenna elements23and23′ from each other.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably a plurality of sets of the antenna elements23and23′ formed in the dielectric substrates21and21′ and a plurality of sets of the feed pins25whose one end is connected to one of the pair of input terminals25aand25bof the antenna elements23and23′ are provided, the plurality of metal posts30constituting the cavity and the conducting rims32and32′ are formed in the lattice shape so as to surround the plurality of sets of the antenna elements23and23′, and the feed unit40is further provided on the side of the ground conductors22and22′ to distribute and feed the excitation signal to the plurality of sets of the antenna elements23and23′ through the plurality of sets of the feed pin25.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably the feed unit40is formed by the feeding dielectric substrate41and the microstrip feed line42. The feeding dielectric substrate41is provided on the side opposite the dielectric substrates21and21′ across the ground conductors22and22′. The microstrip feed line42is formed in the surface of the feeding dielectric substrate41.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably each of the dipole antenna elements23and23′ is formed in the triangular shape while having the predetermined base width WBand the predetermined height LB/2, and the dipole antenna elements23and23′ constitute the bow-tie antenna while vertexes thereof are arranged so as to face each other.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably each of the dipole antenna elements23and23′ is formed in the deformed rhombic shape while having the predetermined projection width WBand the predetermined height LB/2, and the dipole antenna elements23and23′ constitute the bow-tie antenna while vertexes thereof are arranged so as to face each other.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably the resonator is formed by the cavity and the conducting rim, the structural parameters of the resonator and the antenna elements23and23′ are adjusted to set the resonator to the desired resonance frequency, and thereby the frequency characteristic is obtained such that the gain of the linearly polarized antenna is decreased in the predetermined range.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably the structural parameter includes at least one of the internal dimension Lw of the cavity, the rim width LRof the conducting rim, the overall lengths LBof the antenna elements23and23′, and the horizontal width WBof the antenna elements23and23′.

Fifth Embodiment

FIG. 16is a block diagram showing a configuration of a radar apparatus to which a fifth embodiment of the invention is applied.

That is,FIG. 16shows the configuration of a UWB radar apparatus50in which the linearly polarized antennas20and20′ of the above embodiments are used as a transmitting antenna51and a receiving antenna52.

In the radar apparatus50shown inFIG. 16which is a vehicle-mounted radar apparatus, a control unit53performs timing control of a transmitting unit54, the transmitting unit54generates a pulse wave having a carrier frequency of 26 GHz at predetermined periods, and the transmitting antenna51radiates the pulse wave to a space1which is an exploration target.

The receiving antenna52receives the pulse wave reflected from an object1ain the space1, and the received signal is inputted to a receiving unit55.

The control unit53performs timing control of the receiving unit55, and the receiving unit55performs detection processing of the received signal.

The signal obtained by the detection processing is outputted to an analysis processing unit56, analysis processing is performed to the space1of the exploration target, and the control unit53is notified of the analysis result if needed.

The linearly polarized antennas20and20′ can be used as the transmitting antenna51and receiving antenna52of the radar apparatus50having the above configuration.

In the case where the radar apparatus50is mounted on the vehicle, it is desirable that the transmitting antenna51and the receiving antenna52be integrally formed.

FIG. 17shows a linearly polarized antenna60formed in consideration of the above point. From the structural viewpoint, the transmitting antenna51and receiving antenna52formed by the first and second linearly polarized antennas20′ having the same configuration as the linearly polarized antenna20′ ofFIG. 15are provided on the right and left sides of a common landscape-oriented dielectric substrate21″.

FIG. 17is a front view showing a configuration of the linearly polarized antenna60used in the radar apparatus to which the fifth embodiment of the apparatus is applied.

As described above, in the transmitting antenna51and receiving antenna52provided in the linearly polarized antenna60, because each antenna element23is surrounded by the cavity structure formed by the plurality of metal posts30and the conducting rim32′, the surface wave has no influence on the transmitting antenna51and receiving antenna52. Therefore, the transmitting antenna51and receiving antenna52have the broadband gain characteristics and the radiation to the RR radio-wave emission prohibited band is suppressed.

Furthermore, because each of feed units (not shown) of the transmitting antenna51and receiving antenna52ofFIG. 17has the array structure shown inFIG. 15, the good linearly polarized wave characteristic is obtained, and the receiving antenna52can receive the linearly polarized wave reflected from the object1awith high sensitivity. The transmitting antenna51radiates the linearly polarized wave to the exploration space.

The equivalents to the linearly polarized antennas20and20″ may be adopted as the transmitting antenna51and receiving antenna52of the radar apparatus50.

That is, the radar apparatus of the invention is characterized by basically including the transmitting unit54which radiates the radar pulse to the space1via the transmitting antenna51, the receiving unit55which receives the radar pulse wave reflected from the space1via the receiving antenna52, the analysis processing unit56which explores the object1aexisting in the space1based on the receiving output from the receiving unit55, and the control unit53which controls at least one of the transmitting unit54and the receiving unit55based on the output from the analysis processing unit56. In the radar apparatus, the transmitting antenna51and receiving antenna52are formed by the first and second linearly polarized antenna elements23and23′, the first and second linearly polarized antenna elements23and23′ respectively include dielectric substrates21,21′, and21″, the ground conductors22and22′ which are overlapped on one side of each of the dielectric substrates21,21′, and21″, the linearly polarized antenna elements23and23′ which are formed on the opposite surface of the dielectric substrates21,21′, and21″, the plurality of metal posts30whose one end side is connected to the ground conductors22and22′, the plurality of metal posts30piercing through the dielectric substrates21,21′, and21″ along the thickness direction, the other end side of the plurality of metal posts30being extended to the opposite surface of the dielectric substrates21,21′, and21″, the plurality of metal posts30being provided at predetermined intervals to form the cavity so as to surround the antenna elements23and23′, and the conducting rims32and32′ which short-circuit the other end side of each of the plurality of metal posts30on the opposite surface side of the dielectric substrates21,21′, and21″, the conducting rims32and32′ being provided while extended by a predetermined distance in the directions of the antenna elements23and23′. One end side of each of the plurality of metal posts30is connected to the ground conductors22and22′, the plurality of metal posts30pierce through the dielectric substrate21″ along the thickness direction thereof, the other end of the plurality of metal posts30are extended to the opposite surface of the dielectric substrate21″, the plurality of metal posts30are provided at predetermined intervals to form the separated cavities such that the plurality of metal posts30surround the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′ while separating the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′, and the first conducting rim32and second conducting rim32′ are provided as the conducting rims32and32′ on the opposite surface of the dielectric substrate21″, the first conducting rim32and second conducting rim32′ short-circuiting the other end side of each of the plurality of metal posts30along the line direction of the plurality of metal posts30, the plurality of metal posts30being provided at predetermined intervals so as to surround the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′ while separating the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′, the first conducting rim32and second conducting rim32′ being extended by the predetermined distance toward the directions of the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably the antenna elements23and23′ are formed by the dipole antenna elements23and23′ having the pair of input terminals25aand25b, the feed pin25is further provided, one end side of the feed pin25is connected to one of the pair of input terminals25aand25bof the dipole antenna elements23and23′, the other end side of the feed pin25pierces through the dielectric substrate21″ and the ground conductors22and22′, and the other of the pair of input terminals25aand25bof the dipole antenna elements23and23′ pierces through the dielectric substrate21″ and short-circuits the ground conductors22and22′.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably the conducting rims32and32′ have at least a pair of uneven-width portions, e.g., a pair of triangular portions which are located across the antenna elements23and23′ from each other.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably a plurality of sets of the antenna elements23and23′ formed in the dielectric substrate21″ and a plurality of sets of the feed pin25whose one end is connected to one of the pair of input terminals25aand25bof the antenna elements23and23′ are provided, the plurality of metal posts30constituting the cavity and the conducting rims32and32′ are formed in the lattice shape so as to surround the plurality of sets of the antenna elements23and23′, and the feed unit40is further provided on the side of the ground conductors22and22′ to distribute and feed the excitation signal to the plurality of sets of the antenna elements23and23′ through the plurality of sets of the feed pin25.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably the feed unit40is formed by the feeding dielectric substrate41and the microstrip feed line42. The feeding dielectric substrate41is provided on the side opposite the dielectric substrate21″ across the ground conductor22and22′. The microstrip feed line42is formed in the surface of the feeding dielectric substrate41.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably each of the dipole antenna elements23and23′ is formed in the triangular shape while having the predetermined base width WBand the predetermined height LB/2, and the dipole antenna elements23and23′ constitute the bow-tie antenna while vertexes thereof are arranged so as to face each other.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably each of the dipole antenna elements23and23′ is formed in the deformed rhombic shape while having the predetermined projection width WBand the predetermined height LB/2, and the dipole antenna elements23and23′ constitute the bow-tie antenna while vertexes thereof are arranged so as to face each other.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably the resonator is formed by the cavity and the conducting rims32and32′, the structural parameters of the resonator and the antenna elements23and23′ are adjusted to set the resonator to the desired resonance frequency, and thereby the frequency characteristic is obtained such that the gain of the linearly polarized antenna is decreased in the predetermined range.

In addition to the above basic configuration, the radar apparatus of the invention is characterized in that preferably the structural parameter includes at least one of the internal dimension Lw of the cavity, the rim width LRof the conducting rims32and32′, the overall lengths LBof the antenna elements23and23′, and the horizontal width WBof the antenna elements23and23′.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23′ and23are formed as the antenna element in the dielectric substrate21″, one end side of each of the plurality of metal posts30is connected to the ground conductor22, each of the plurality of metal posts30pierces through the dielectric substrate21″ along the thickness direction thereof, the other end side of each of the plurality of metal posts30is extended to the opposite surface of the dielectric substrate21″, the plurality of metal posts30are provided at predetermined intervals to form the separated cavities such that the plurality of metal posts30surround the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′ while separating the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′, and the first conducting rim32and second conducting rim32′ are provided as the conducting rims32and32′ on the opposite surface of the dielectric substrate21″, the first conducting rim32and second conducting rim32′ short-circuiting the other end side of each of the plurality of metal posts30along the line direction thereof, the plurality of metal posts30being provided at predetermined intervals so as to surround the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′ while separating the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′, the first conducting rim32and second conducting rim32′ being extended by the predetermined distance toward the directions of the first linearly polarized antenna elements23and23′ and the second linearly polarized antenna elements23and23′.

In addition to the above basic configuration, the linearly polarized antenna of the invention is characterized in that preferably one of the first linearly polarized antenna element23or23′ and the second linearly polarized antenna element23or23′ is applied to the transmitting antenna51of the radar apparatus50while the other is applied to the receiving antenna52of the radar apparatus50.

INDUSTRIAL APPLICABILITY

The fifth embodiment is the example in which the linearly polarized antenna of the invention is used as the UWB radar apparatus. In addition to the UWB radar apparatus, the linearly polarized antenna of the invention can also be applied to various communication systems in frequency bands other than UWB.