Thin cavity antenna

Abstract

To provide a thin cavity-equipped antenna capable of achieving high gain in a unidirectional manner over a wide frequency band by adding a cavity to an antenna radiating element.SOLUTION: A thin cavity-equipped antenna 11 of the present disclosure has a printed circuit board 111 having a first plane Ps1 perpendicular to a first direction X1, a radiating element 112 provided on the first plane Ps1 of the printed circuit board 111, comprising a conductor and radiating radio waves in the first direction X1, a cavity 113 provided on the opposite side of the radiating element 112 from the first direction X1, comprising a conductor and having a concave shape opposite to the first direction X1, and a power feed circuit 114 that feeds power to the radiating element 112, and the first length L1 in the first direction X1 of the cavity 113 is less than 1 / 10 of the second length L2 in the second direction X2 orthogonal to the first direction X1 of the cavity 113.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to a thin cavity-equipped antenna, and more particularly to a thin cavity-equipped antenna that can achieve unidirectionality and high gain over a wide frequency band by adding a cavity to the antenna radiating element. [Background technology]

[0002] Spiral antennas and sinusoidal antennas are known as antennas that are flat and thin and can be used over a wide frequency band. When these antennas are used for communication or radio wave monitoring, the radiation characteristics of the antenna must be unidirectional.

[0003] For example, when using a spiral antenna to achieve a unidirectional antenna, one method is to install a planar (flat) spiral element horizontally and install a "basin-shaped cavity" made of a conductor below the spiral element. This method allows radio waves to be radiated only upward, achieving unidirectionality. This method is described in Figure 5 of Patent Document 1. An antenna with a basin-shaped cavity installed below the spiral element is called a cavity-equipped antenna.

[0004] In this method, the cavity is placed below the radiating element, and the distance from the spiral element to the bottom of the cavity is approximately 1 / 4 of the wavelength used. By doing so, the radio waves reflected at the bottom of the cavity are in phase with the radio waves radiated upward from the spiral element, and the radio waves reinforce each other, achieving unidirectionality.

[0005] However, when the frequency band in use is wide, for example, at a frequency twice the lowest frequency in use, the wavelength is 1 / 2, and the distance between the spiral element and the bottom of the cavity is 1 / 2 wavelength. In this case, the radio waves reflected at the bottom of the cavity are in opposite phase to the radio waves radiated upward from the spiral element, so the directivity of the upward radiation has a large null, which is a problem.

[0006] Specific examples of the above are given below. Assuming a wideband antenna with a frequency range of 1 to 6 GHz (gigahertz), the minimum operating frequency is 1 GHz and the wavelength is 300 mm (millimeters). In this case, the depth of the cavity is set to 75 mm, which is 1 / 4 of the wavelength. Under these conditions, the radio waves reflected from the bottom of the cavity will be in phase with the radio waves emitted upward from the spiral element, making the antenna unidirectional.

[0007] The reason why the phases are the same will be explained below. The path length for radio waves emitted downward, reflected by the bottom of the cavity, and returning to the original emission point is (1 / 4) wavelength round trip, so (1 / 2) wavelength. Converted to phase, this results in a delay of 180 degrees. Furthermore, when radio waves are reflected by the metal plate at the bottom of the cavity, the phase is inverted, that is, the phase rotates 180 degrees, resulting in a phase inversion. This results in a total phase rotation of 360 degrees, and the radio waves emitted upwards from the antenna and the radio waves reflected by the bottom of the cavity are in phase.

[0008] However, when using a frequency of 2 GHz, the wavelength is 150 mm, which corresponds to half the wavelength of the cavity depth. In this case, the radio waves reflected from the bottom of the cavity experience a phase delay of one wavelength, or 360 degrees, on the round trip from the bottom of the cavity. In addition, a 180-degree phase reversal occurs upon reflection. As a result, the radio waves radiating upward from the spiral element and the radio waves reflected from the bottom of the cavity are out of phase and cancel each other out, creating a null in the main beam and making it difficult to achieve unidirectionality.

[0009] When the frequency is 4 GHz, the wavelength is 75 mm, and the radio waves reflected at the bottom of the cavity are delayed by two wavelengths, or 720 degrees, on the round trip, and undergo a phase reversal of 180 degrees upon reflection. As a result, the radio waves radiated upward from the spiral element and the radio waves reflected at the bottom of the cavity are out of phase and cancel each other out, creating a null in the main beam and making it difficult to achieve unidirectionality.

[0010] When the frequency is 6 GHz, the wavelength is 50 mm, and the radio waves reflected at the bottom of the cavity are delayed by three wavelengths, or 1080 degrees, on the round trip, and undergo a phase reversal of 180 degrees upon reflection. As a result, the radio waves radiated upward from the spiral element and the radio waves reflected at the bottom of the cavity are out of phase and cancel each other out, creating a null in the main beam and making it difficult to achieve unidirectionality.

[0011] As can be understood from the above explanation, at frequencies where the depth of the cavity is an integral multiple of (1 / 2) wavelength, a null occurs in the main beam, making it difficult to achieve unidirectionality.

[0012] Thus, the commonly used "tub-shaped cavity" has the problem (issue) of making it difficult to achieve unidirectionality over a wide band. One method of solving this problem, as described in Patent Documents 1 and 2, for example, is to place a radio wave absorber inside the cavity, absorb the radio waves radiated downward from the spiral antenna with the radio wave absorber, and reduce the radio waves reflected at the bottom of the cavity.

[0013] However, this method has the problem that it is not possible to obtain a large gain because the radio waves radiated downward are absorbed by a radio wave absorber. When this antenna is used for transmission, about half of the transmitted power is lost, and when it is used for reception, the radio wave absorber causes a deterioration in noise temperature.

[0014] Therefore, to solve this problem (shortcoming), it is necessary to avoid placing a radio wave absorber inside the cavity and to devise a cavity shape that will achieve unidirectional upward direction over a wide bandwidth.

[0015] One method for solving this problem is to make the cross-sectional shape of the cavity a cone-shaped curved surface, which makes it possible to maintain unidirectionality over a wide frequency range, as described in Non-Patent Document 1. However, this method has the problem that it is expensive because the manufacturing of the cavity cross-section is complicated.

[0016] The above explains the problems with cavity-backed antennas and how to solve them. To summarize, when a tub-shaped cavity is used for a cavity-backed antenna, a null occurs in the main beam at high frequencies. Furthermore, when a radio wave absorber is used inside the cavity, the gain decreases, power loss increases during transmission, and the noise temperature increases during reception. Furthermore, when a cavity with a cone-shaped curved surface is used, it is possible to form a unidirectional pattern over a wide bandwidth, but the price is high. [Prior art documents] [Patent documents]

[0017] [Non-Patent Document 1] Title of the paper: "Optimization of a two-wire spiral antenna with a cone-shaped cavity" Name of the conference: Institute of Electronics, Information and Communication Engineers 2022 General Conference Paper published: Proceedings of the Institute of Electronics, Information and Communication Engineers 2022 Society Conference B-1-79 [Patent Document 1] Japanese Patent Application Publication No. 63-208309 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-94321 Summary of the Invention [Problem to be solved by the invention]

[0018] As described above, it is difficult to realize a thin cavity-equipped antenna that is unidirectional and has high gain over a wide frequency band using the techniques described in Patent Document 1, Patent Document 2, and Non-Patent Document 1, and such an antenna has been desired. Also, an inexpensive antenna that has good matching characteristics has been desired.

[0019] An object of the present disclosure is to provide a low-profile cavity-backed antenna that solves any of the above-mentioned problems. [Means for solving the problem]

[0020] The thin cavity-equipped antenna according to the present disclosure comprises: a printed circuit board having a first surface perpendicular to a first direction; a radiating element provided on a first surface of the printed circuit board, the radiating element being made of a conductor and radiating radio waves in the first direction; a cavity provided on the opposite side of the radiating element from the first direction, the cavity being made of a conductor and having a concave shape in the opposite direction from the first direction; a feeding circuit for feeding the radiating element; Equipped with A first length of the cavity in the first direction is equal to or less than one-tenth of a second length of the cavity in a second direction perpendicular to the first direction. [Effects of the Invention]

[0021] According to the present disclosure, by adding a cavity to an antenna radiating element, it is possible to provide a thin cavity-equipped antenna that can achieve unidirectionality and high gain over a wide frequency band. [Brief explanation of the drawings]

[0022] [Figure 1A] 1 is a perspective view illustrating a thin cavity-equipped antenna according to a first embodiment. [Figure 1B] 1 is a cross-sectional view illustrating a thin cavity-equipped antenna according to a first embodiment. [Figure 2A] 1 is a side view illustrating a feed circuit of the thin cavity-equipped antenna according to the first embodiment. FIG. [Figure 2B] 1 is a perspective view illustrating a feed circuit of a thin cavity-equipped antenna according to a first embodiment. FIG. [Figure 2C] 1 is a perspective view illustrating a feed circuit of a thin cavity-equipped antenna according to a first embodiment. FIG. [Figure 3] 1 is a cross-sectional view illustrating a thin cavity-equipped antenna according to a first embodiment. [Figure 4] 2 is a schematic diagram illustrating the operation principle of the thin cavity-equipped antenna according to the first embodiment. FIG. [Figure 5A]1 is a perspective view illustrating a simulation model of the thin cavity-equipped antenna according to the first embodiment. FIG. [Figure 5B] 3 is a cross-sectional view illustrating a simulation model of the thin cavity-equipped antenna according to the first embodiment. FIG. [Figure 6A] FIG. 5B is a top view of the spiral element shown in FIG. 5A as viewed from above. [Figure 6B] FIG. 6B is an enlarged view of the central portion of the spiral element shown in FIG. 6A. [Figure 7A] 4 shows the results of a simulation of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. [Figure 7B] 4 shows the results of a simulation of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. [Figure 7C] 4 shows the results of a simulation of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. [Figure 7D] 4 shows the results of a simulation of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. [Figure 7E] 4 shows the results of a simulation of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. [Figure 7F] 4 shows the results of a simulation of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. [Figure 8A] 4 is a graph illustrating the frequency characteristics of the voltage standing wave ratio (VSWR) of a prototype of the thin cavity-equipped antenna according to the first embodiment. [Figure 8B] 4 is a graph illustrating frequency characteristics of gain and axial ratio of a prototype of the thin cavity-equipped antenna according to the first embodiment. [Figure 9] 4 is a graph illustrating a radiation pattern of a prototype of the thin cavity-equipped antenna according to the first embodiment. [Figure 10] 1A and 1B are schematic diagrams illustrating the operating principle of a thin cavity-equipped antenna according to a comparative example. [Figure 11A]FIG. 10 is a perspective view illustrating a simulation model of a thin cavity-equipped antenna according to a comparative example. [Figure 11B] FIG. 10 is a cross-sectional view illustrating a simulation model of a thin cavity-equipped antenna according to a comparative example. [Figure 12A] 10 shows the results of a simulation of the three-dimensional radiation pattern of a thin cavity-backed antenna according to a comparative example. [Figure 12B] 10 shows the results of a simulation of the three-dimensional radiation pattern of a thin cavity-backed antenna according to a comparative example. [Figure 12C] 10 shows the results of a simulation of the three-dimensional radiation pattern of a thin cavity-backed antenna according to a comparative example. [Figure 13A] FIG. 10 is a perspective view illustrating a thin cavity-equipped antenna according to a second embodiment. [Figure 13B] 10 is a cross-sectional view illustrating a thin cavity-equipped antenna according to a second embodiment. FIG. [Figure 14] 10 is a cross-sectional view illustrating a thin cavity-equipped antenna according to a third embodiment. FIG. [Figure 15A] 10A and 10B are a plan view illustrating a thin cavity-equipped antenna according to a fourth embodiment and a perspective view illustrating a cavity. [Figure 15B] 10A and 10B are a plan view illustrating a thin cavity-equipped antenna according to a fourth embodiment and a perspective view illustrating a cavity. [Figure 16A] 10A and 10B are perspective views illustrating a radiating element and a thin cavity-equipped antenna according to a fourth embodiment. [Figure 16B] 10A and 10B are perspective views illustrating a radiating element and a thin cavity-equipped antenna according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0024] [Embodiment 1] <Configuration> FIG. 1A is a perspective view illustrating a thin cavity-equipped antenna according to a first embodiment. FIG. 1B is a cross-sectional view illustrating the thin cavity-equipped antenna according to the first embodiment. 1A, 1B, and subsequent drawings, the upward direction is referred to as the first direction X1, the direction perpendicular to the first direction X1 is referred to as the second direction X2, and the direction perpendicular to the first direction X1 and the second direction X2 is referred to as the third direction X3, as necessary.

[0025] 1A and 1B, the thin cavity-equipped antenna 11 according to the first embodiment includes a radiating element 112 and a cavity 113. The depth L1 of the cavity 113 is approximately 1 / 10 of the diameter L2 of the cavity 113 or less.

[0026] In detail, the thin cavity-equipped antenna 11 includes a printed circuit board 111, a radiating element 112, a cavity 113, and a feed circuit 114. The printed circuit board 111 has a first surface Ps1 perpendicular to a first direction X1. The radiating element 112 is provided on the first surface Ps1 of the printed circuit board 111, is made of a conductor, and radiates radio waves in the first direction X1. The cavity 113 is provided on the opposite side of the radiating element 112 from the first direction X1, is made of a conductor, and has a concave shape in the direction opposite to the first direction X1. The feed circuit 114 feeds power to the radiating element 112. A first length L1 of the cavity 113 in the first direction X1 is equal to or less than one-tenth of a second length L2 of the cavity 113 in a second direction X2 perpendicular to the first direction X1.

[0027] The depth of cavity 113 may also be referred to as the first length of cavity 113 in the first direction X1. The diameter of cavity 113 may also be referred to as the second length of cavity 113 in the second direction X2. A concave cavity may also be referred to as a "basin-shaped cavity."

[0028] Radiating element 112 has first element 1121 and second element 1122. First element 1121 is provided as a conductor pattern on first surface Ps1 of printed circuit board 111, and has a spiral shape when viewed from first direction X1. Second element 1122 is provided as another conductor pattern on first surface Ps1 of printed circuit board 111, and forms a pair of spiral shapes with first element 1121 when viewed from first direction X1. A portion of second element 1122 is disposed between a portion of first element 1121 and another portion of first element 1121.

[0029] The conductor pattern may be, for example, a copper foil pattern formed of copper foil. Therefore, radiating element 112 may be configured with a pair of spiral-shaped copper foil patterns formed by etching copper foil on the upper surface (first surface Ps1) of printed circuit board 111. The radius of curvature of the spiral of radiating element 112 increases from the start point (center) of the spiral toward the end point.

[0030] The pair of spiral-shaped conductor patterns may be arranged on the back surface (second surface Ps2) of printed circuit board 111. Alternatively, one of the pair (for example, first element 1121) may be arranged on the top surface, and the other (for example, second element 1122) may be arranged on the bottom surface. In addition, in the first embodiment, a printed circuit board is used to hold the spiral-shaped conductor patterns, but this is not limiting. A structure that can hold the spiral shape of radiating element 112, such as a structure that holds it using plastic, may also be used.

[0031] Other forms of radiating element 112 include a single-wire spiral antenna made up of a single spiral-shaped conductor, and a four-wire spiral antenna made up of four spiral-shaped conductors.

[0032] FIG. 2A is a side view illustrating a feed circuit of the thin cavity-equipped antenna according to the first embodiment. FIG. 2B is a perspective view illustrating a feed circuit of the thin cavity-equipped antenna according to the first embodiment. FIG. 2C is a perspective view illustrating a feed circuit of the thin cavity-equipped antenna according to the first embodiment.

[0033] 2A to 2C, the power supply circuit 114 has a first conductor 1141, a second conductor 1142, and a dielectric layer 1143. The dielectric layer 1143 is made of a dielectric material. The first conductor 1141 is provided on a first surface Ds1 of the dielectric layer 1143 and is made of a conductor. The second conductor 1142 is provided on a second surface Ds2 of the dielectric layer 1143 and is made of a conductor.

[0034] One end of first conductor 1141 is connected to one end near the center of the spiral shape of first element 1121. A high-frequency signal is connected to the other end of first conductor 1141. One end of second conductor 1142 is connected to one end near the center of the spiral shape of second element 1122. The other end of second conductor 1142 is connected to ground.

[0035] The length of the second conductor 1142 in the third direction X3, i.e., the width of the second conductor 1142, increases from one end of the second conductor 1142 to the other end of the second conductor 1142. The third direction X3 is perpendicular to the first direction X1 and the second direction X2.

[0036] The power supply circuit 114 is formed by etching a printed circuit board having copper foil on a first surface Ds1, which is the front surface, and a second surface Ds2, which is the back surface. The copper foil pattern of the first conductor 1141 has the shape of a normal microstrip line. The copper foil pattern of the second conductor 1142 is a tapered copper foil pattern, which allows for simultaneous balanced-to-unbalanced conversion and impedance conversion (matching).

[0037] If balanced-to-unbalanced conversion is not required or impedance matching is not required, a coaxial cable (not shown) may be used to connect to radiating element 112 instead of feed circuit 114 .

[0038] FIG. 3 is a cross-sectional view illustrating the thin cavity-equipped antenna according to the first embodiment. FIG. 3 shows an example of the low-profile cavity antenna shown in FIG. 1B.

[0039] As shown in FIG. 3, the thin cavity-equipped antenna 11 is fed by a feeding circuit 114 via a first conductor 1141 and a second conductor 1142 at the center of a spiral-shaped copper foil pattern (radiating element 112).

[0040] The cavity 113 has a bottom 1131 having a plane perpendicular to the first direction X1, and a side surface 1132 extending from the periphery of the bottom 1131 in the first direction X1.

[0041] The thin cavity-equipped antenna 11 further includes a coaxial connector 115 provided at the bottom 1131 of the cavity 113. The other end of the first conductor 1141 is connected to the core wire of the coaxial connector 115. The other end of the second conductor 1142 is connected to the ground of the coaxial connector 115.

[0042] <Operating principle> The operating principle of the thin cavity-equipped antenna 11 will now be described. FIG. 4 is a schematic diagram illustrating the operating principle of the thin cavity-equipped antenna according to the first embodiment. FIG. 4 shows a cross-sectional view.

[0043] As shown in FIG. 4, the thin cavity-equipped antenna 11 has a cavity 113 whose length (depth) L1 in the first direction X1 is very thin (short) and is less than (1 / 10) of the cavity 113's length (diameter) L2 in the second direction X2.

[0044] When radio waves are radiated from the radiating element 112 of the thin cavity-mounted antenna 11, there are upward radiation components radiated upward (first direction X1) and downward radiation components radiated downward. The downward radiation components are reflected by the bottom surface of the cavity 113 and radiated upward. The downward radiation components have an opposite phase when reflected by the bottom surface. As a result, the upward radiation components and the opposite-phase bottom-reflected components (downward radiation components) are combined.

[0045] In the case of the thin cavity-equipped antenna 11 according to embodiment 1, the depth L1 of the cavity 113 is very thin, being less than (1 / 10) of the diameter L2 of the cavity 113, but due to the phase difference in this thin portion, the upward radiation component and the downward radiation component do not cancel each other out, and no null occurs in the main beam.

[0046] FIG. 5A is a perspective view illustrating a simulation model of the thin cavity-equipped antenna according to the first embodiment. FIG. 5B is a cross-sectional view illustrating a simulation model of the thin cavity-equipped antenna according to the first embodiment.

[0047] 5A and 5B, for example, a spiral element is used as the radiating element 112. The outermost diameter Sd of the spiral element is equal to the wavelength λ of the lowest frequency used. L is 0.6 times, 0.60λ L The diameter L2 of the cavity 113 is set to be about 10% larger than the diameter Sd to reduce the influence on the radiating element 112, and is set to 0.67λ L The thin cavity antenna 11 is characterized in that the depth L1 of the cavity 113 is equal to or less than 1 / 10 of the diameter L2 of the cavity 113. Therefore, the depth L1 of the cavity 113 is 0.067λ. L Let's say.

[0048] Consider the operation of the thin cavity-backed antenna 11 under these dimensions. The upward radiation component and the downward radiation component reflected from the bottom are combined in the direction of the main beam radiated upward. At this time, the path difference (propagation path difference) between the upward radiation component and the downward radiation component is 0.067λ at the lowest operating frequency. L ×2 times (round trip) = 0.134λ L This corresponds to a phase difference of approximately 48 degrees. When reflected at the bottom surface, the phase is inverted, so if we take into account the 180 degrees that is involved, the phase difference between the upward radiation component and the downward radiation component is 48 degrees + 180 degrees = 228 degrees, and they are not out of phase. Therefore, no null occurs in the upward radiation pattern.

[0049] Consider the case where the minimum operating frequency is 1 GHz. If the minimum operating frequency is 1 GHz, the diameter L2 of the cavity 113 is 200 mm, the outermost diameter Sd of the spiral element is 180 mm, and the depth L1 of the cavity 113 is 20 mm.

[0050] Let's consider the case where the minimum usable frequency is 2GHz. The wavelength λ2 of a frequency of 2GHz is half the wavelength λ1 of a frequency of 1GHz. In other words, 2×λ2=λ L Therefore, the path difference between the upward radiation component and the downward radiation component is 0.134λ L =0.268λ2, which translates to a phase difference of approximately 96 degrees. When reflected at the bottom, the phase is inverted, so if we take into account the 180 degrees that is involved, the phase difference between the upward and downward radiation components is 96 degrees + 180 degrees = 276 degrees, and they are not out of phase. Therefore, no null occurs in the upward radiation pattern.

[0051] Let's consider the case where the minimum usable frequency is 3GHz. The wavelength λ3 of the frequency 3GHz is (1 / 3) of the wavelength λ1 of the frequency 1GHz. In other words, 3×λ3=λ L Therefore, the path difference between the upward radiation component and the downward radiation component is 0.134λ L =0.402λ3, which translates to a phase difference of approximately 144 degrees. When reflected from the bottom surface, the phase is inverted, so if we take into account the 180 degrees that is involved, the phase difference between the upward and downward radiation components is 144 degrees + 180 degrees = 324 degrees, which means that they are not out of phase but close to being in phase. Therefore, no nulls occur in the upward radiation pattern.

[0052] Let's consider the case where the minimum usable frequency is 6GHz. The wavelength λ6 of the frequency 6GHz is (1 / 6) of the wavelength λ1 of the frequency 1GHz. In other words, 6×λ6=λ L Therefore, the path difference between the upward radiation component and the downward radiation component is 0.134λ L=0.804λ6, which converts to a phase difference of approximately 289 degrees. When reflected at the bottom, the phase is inverted, so if we take into account the 180 degrees that is involved, the phase difference between the upward and downward radiation components is 289 degrees + 180 degrees = 469 degrees. Subtracting 360 degrees leaves us with 109 degrees, so the phases are not reversed. Therefore, no nulls occur in the upward radiation pattern.

[0053] In terms of the relationship between the lowest operating frequency and the cavity depth, the upward radiation component and the downward radiation component are in anti-phase when the depth L1 of the cavity 113 is approximately 1 / 2 wavelength. That is, when the depth L1 is 20 mm, 20 mm x 2 = 40 mm is the frequency where one wavelength is, so a null occurs at 7.5 GHz. However, in reality, the beam shape deteriorates in the upward radiation pattern at frequencies slightly lower than the frequency at which they are completely anti-phase.

[0054] From the above explanation, it can be understood that the thin cavity-equipped antenna 11 shown in Figures 5A and 5B is a wideband antenna that has a beam without nulls in the upward direction (front direction) with a frequency range of 1 GHz to 7 GHz and a relative bandwidth of 150%. Note that Figures 5A and 5B are merely examples, and are not limited to the frequencies and dimensions shown therein.

[0055] <Simulation> To demonstrate the effect of the thin cavity-backed antenna 11, simulation results will be described.

[0056] (Simulation conditions) As shown in Figure 5A, the minimum operating frequency is 1 GHz. In this case, the wavelength λ L The cavity 113 is made of a conductor, and the diameter L2 of the cavity 113 is 200 mm (0.67λ L The outermost diameter Sd of the spiral element, which is the radiating element 112, is 180 mm (0.60 λ L )

[0057] As shown in FIG. 5B, the depth L1 of the cavity 113 is 20 mm (0.067 λ L ), which is (1 / 10) of the diameter L2 of the cavity 113. The spiral element is a two-wire spiral, and its parameters are spiral coefficient: 1.78, number of turns (number of windings): 8, initial radius: 1 mm, and element wire diameter: 1 mm.

[0058] FIG. 6A is a top view of the spiral element shown in FIG. 5A as seen from above. FIG. 6B is an enlarged view of the central portion of the spiral element shown in FIG. 6A. 6A and 6B, the specific dimensional relationship of the spiral element is shown on an XY coordinate system to make it easier to understand. The second direction X2 and the X-axis direction are the same direction. The third direction X3 and the -Y-axis direction are the same direction. The -Y-axis direction is the opposite direction to the Y-axis direction.

[0059] As shown in Figures 6A and 6B, in this example, a two-wire spiral antenna is used as the spiral element. In a two-wire spiral antenna, two spirals (vortices) are arranged rotating in the same direction. This spiral is called an Archimedes spiral, and the radius R from the center of the spiral is defined by the following equation. For convenience of explanation, the spiral may also be called a spiral.

[0060] R=Ro+a×θ (1) However, R О : initial radius, a: spiral coefficient, θ: rotation angle from the X axis.

[0061] initial radius R О is the distance between the center and the coordinate of the starting point of the spiral. In Figures 6A and 6B, the starting point of the spiral starts from the point on the X axis where Y = 0, so the distance from 0 to 1 on the X axis, i.e., 1 is the initial radius R ОAs can be seen from equation (1), the radius R of the spiral element curve increases as the rotation angle θ from the X-axis increases, resulting in a spiral shape. The spiral coefficient a is a coefficient that indicates the degree to which the spiral spreads. Figures 6A and 6B show a spiral element with a number of turns, i.e., the number of spiral windings, of 8. One rotation is represented by a rotation angle θ = 2π, so the end point is θ = 2π × 8 = 16π. In this example, a two-wire spiral antenna is constructed by rotating the spiral starting from coordinates (1,0) by 180 degrees point-symmetrically. The thickness of the element wire diameter is the thickness of the spiral.

[0062] (Simulation results) FIG. 7A shows a simulation result of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. FIG. 7B shows a simulation result of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. FIG. 7C shows a simulation result of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. FIG. 7D shows a simulation result of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. FIG. 7E shows a simulation result of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment. FIG. 7F shows a simulation result of a three-dimensional radiation pattern of the thin cavity-backed antenna according to the first embodiment.

[0063] 7A to 7F show simulation results for frequencies from 1 GHz to 6 GHz. In each of Figures 7A to 7F, right-handed circular polarization is shown. The vertical axis in each of Figures 7A to 7F represents directional gain.

[0064] As shown in Figures 7A to 7F, the radiation pattern exhibits broad (broadband) directivity without side lobes at any frequency from 1 GHz to 6 GHz, and it can be seen that there is no null in the front direction (Z direction). In this way, by using the thin-type cavity-backed antenna 11, a wideband radiation pattern without a null in the front direction can be obtained over a wide band. As a result, it is possible to provide a thin-type cavity-backed antenna that can achieve unidirectionality and high gain over a wide frequency band.

[0065] Furthermore, the thin cavity-equipped antenna 11 does not use an absorbing element as used in the techniques described in Patent Documents 1 and 2. This reduces the loss due to the radio wave absorber, making it possible to achieve a wide band, low loss, and good noise temperature characteristics.

[0066] Furthermore, the thin cavity-equipped antenna 11 can achieve a wideband unidirectional pattern and high gain without making the cross section of the cavity a cone-shaped curved surface as described in Non-Patent Document 1. Making the cross section of the cavity a cone-shaped curved surface makes manufacturing the cavity cross section complicated and expensive. Therefore, the thin cavity-equipped antenna 11 has a simple structure and can be manufactured inexpensively.

[0067] <Prototype measurement results> To demonstrate the effect of the thin cavity-backed antenna 11, the measurement results of a prototype are shown below.

[0068] The dimensions of the prototype of the thin cavity-backed antenna 11 were those shown in Figures 5A and 5B (simulation model). That is, the dimensions of the prototype were as follows: diameter L2 of cavity 113 = 200 mm, outermost diameter Sd of the spiral element = 180 mm, and depth L1 of cavity 113 = 20 mm. The parameters of the spiral element were also the same as those shown in Figures 5A and 5B. A feed circuit was also provided in the center of the spiral element.

[0069] FIG. 8A is a graph illustrating the frequency characteristics of the voltage standing wave ratio (VSWR) of a prototype of the thin cavity-equipped antenna according to the first embodiment. FIG. 8A shows the measurement results of the prototype. The horizontal axis of FIG. 8A represents frequency (GHz), and the vertical axis represents VSWR.

[0070] As shown in Figure 8A, a VSWR of <3.5 can be achieved in the frequency range of 0.7 GHz to 12.5 GHz, and a VSWR of <2.0 can be achieved in the frequency range of 1.9 GHz to 6.2 GHz. The relative bandwidth where the VSWR is <2.0 is 106%. The thin cavity-backed antenna 11 can achieve good input impedance characteristics over a wide band.

[0071] FIG. 8B is a graph illustrating frequency characteristics of gain and axial ratio of a prototype of the thin cavity-equipped antenna according to the first embodiment. FIG. 8B shows the measurement results of the prototype. The horizontal axis of FIG. 8B represents frequency (GHz), and the vertical axis represents gain (dBic) and axial ratio (dB).

[0072] As shown in Figure 8B, the antenna gain is 0 dBic or more at frequencies between 1 GHz and 8.1 GHz, and 6 dBic or more at frequencies between 1.2 GHz and 6.8 GHz. In particular, a nearly flat antenna gain can be obtained at frequencies between 1.2 GHz and 6.8 GHz. The axial ratio is 3 dB or less at frequencies between 2.1 GHz and 7 GHz, and good circular polarization characteristics can be obtained.

[0073] FIG. 9 is a graph illustrating the radiation pattern of a prototype of the thin cavity-equipped antenna according to the first embodiment. Figure 9 shows the measurement results of the prototype. The horizontal axis in FIG. 9 represents the angle (degrees), and the vertical axis represents the gain (dBic).

[0074] As shown in FIG. 9, a broad radiation pattern without nulls in the front direction (first direction X1 in FIG. 5A) can be obtained at any of the frequencies of 1.5 GHz, 3 GHz, 4.5 GHz, and 6 GHz.

[0075] As explained with reference to FIGS. 8A, 8B and 9, the thin cavity-equipped antenna 11 can provide the following effects (features). -It is a wideband and thin antenna. - Maintains unidirectionality over a wide bandwidth. Maintains high gain over a wide bandwidth. -Wide bandwidth, maintains good input impedance characteristics. Wideband, low loss, and maintains good noise temperature characteristics. The antenna has a simple structure and can be manufactured inexpensively.

[0076] [Comparative Example] A thin cavity-equipped antenna according to a comparative example of the first embodiment will be described. <Operating principle> FIG. 10 is a schematic diagram illustrating the operation principle of a thin cavity-equipped antenna according to a comparative example of the first embodiment.

[0077] As shown in FIG. 10, the thin cavity-equipped antenna 51 according to the comparative example is different from the thin cavity-equipped antenna 11 according to the comparative example of the first embodiment in that the depth L1 of the cavity 513 is longer.

[0078] When radio waves are radiated from the radiating element 512 of the thin cavity-equipped antenna 51 according to the comparative example, there are an upward radiation component that radiates upward and a downward radiation component that radiates downward. The downward radiation component is reflected by the bottom surface of the cavity 513 and radiated upward. The downward radiation component has an opposite phase when reflected by the bottom surface. As a result, the upward radiation component and the opposite-phase bottom-reflected component (downward radiation component) are combined, which cancel each other out, generating a null in the main beam. Note that the upward radiation component and downward radiation component have an opposite phase at a frequency where the depth L1 of the cavity 513 is an integer multiple of (1 / 2) the wavelength.

[0079] <Simulation results> FIG. 11A is a perspective view illustrating a simulation model of a thin cavity-equipped antenna according to a comparative example. FIG. 11B is a cross-sectional view illustrating a simulation model of a thin cavity-equipped antenna according to a comparative example.

[0080] As shown in Figures 11A and 11B, radiating element 512 uses one similar to that of thin-type cavity-equipped antenna 11 according to embodiment 1 (see Figures 5A and 5B). The parameters used are those shown in Figures 5A and 5B. Diameter L2 of cavity 513 is 200 mm, and depth L1 of cavity 513 is 75 mm. This value corresponds to (1 / 4) wavelength of the minimum operating frequency of 1 GHz.

[0081] It has already been explained that when the depth L1 of the cavity 513 corresponds to (1 / 4) wavelength of the minimum operating frequency of 1 GHz, nulls occur in the front direction (upward direction) of the radiation pattern at frequencies near 2 GHz, 4 GHz, and 6 GHz.

[0082] FIG. 12A shows the simulation results of the three-dimensional radiation pattern of the thin cavity-backed antenna according to the comparative example. FIG. 12B shows the simulation results of the three-dimensional radiation pattern of the thin cavity-backed antenna according to the comparative example. FIG. 12C shows the simulation results of the three-dimensional radiation pattern of the thin cavity-backed antenna according to the comparative example. 12A to 12C show the simulation results for frequencies of 1 GHz, 4 GHz, and 6 GHz.

[0083] As shown in Figure 12A, a broadband three-dimensional radiation pattern is obtained at a frequency of 1 GHz. However, at a frequency of 4 GHz shown in Figure 12B and at a frequency of 6 GHz shown in Figure 12C, a null occurs in the upward direction (Z direction).

[0084] The thin cavity-fitted antenna 51 according to the comparative example has a null in the Z direction at frequencies of 4 GHz and 6 GHz. As a result, it is difficult for the comparative example to provide a thin cavity-fitted antenna that can achieve unidirectionality and high gain over a wide frequency band.

[0085] [Embodiment 2] FIG. 13A is a perspective view illustrating a thin cavity-equipped antenna according to the second embodiment. FIG. 13B is a cross-sectional view illustrating the thin cavity-equipped antenna according to the second embodiment.

[0086] 13A and 13B, the thin-type cavity-equipped antenna 21 according to the second embodiment differs from the first embodiment in that the length H1 of the feed circuit 214 is longer than the length of the feed circuit 114 according to the first embodiment. To achieve this, the length H1 of the feed circuit 214 in the first direction X1 may be made longer than a predetermined length.

[0087] The cavity 213 has a first portion and a second portion. The first portion is a portion where the length of the cavity 213 in the second direction X2 is longer than the length Pd of the printed circuit board 211 in the second direction X2. The second portion is a portion where the length of the cavity 213 in the second direction X2 is shorter than the length Pd of the printed circuit board 211 in the second direction X2. The length H1 of the power supply circuit 214 in the first direction X1 may be longer than the length Hfeed of the second portion of the cavity 213 in the first direction X1.

[0088] Specifically, in order to accommodate the longer feed circuit 214 compared to the first embodiment, the thin-type cavity-equipped antenna 21 has a feed circuit protrusion (second portion) at the center of the bottom surface of the cavity 213, which has a structure that protrudes downward (in the opposite direction to the first direction X1). The diameter Dfeed of the feed circuit protrusion may be the minimum dimension that can accommodate the feed circuit 214, and may be approximately 1 / 10 of the length L2 of the first portion of the cavity 213 in the second direction X2. Since the matching characteristics improve as the feed circuit 214 becomes longer, the depth Hfeed is set to an appropriate length depending on the application. The sum of the depth L1 of the first portion of the cavity 213 and the depth Hfeed of the feed circuit protrusion is preferably, for example, approximately 1 / 4 of the wavelength of the lowest operating frequency or more.

[0089] The convex portion for the power feed circuit of the cavity 213 may also be referred to as the second portion of the cavity 213. The length of the first portion of the cavity 213 in the second direction X2 may also be referred to as the diameter of the cavity. Furthermore, the length of the second portion of the cavity 213 in the first direction X1 may also be referred to as the depth of the convex portion for the power feed circuit of the cavity 213.

[0090] In the second embodiment, the matching characteristics can be optimized by adjusting the depth of the feeder circuit protrusion.

[0091] [Embodiment 3] FIG. 14 is a cross-sectional view illustrating a thin cavity-equipped antenna according to the third embodiment.

[0092] As shown in FIG. 14, the thin cavity-equipped antenna 31 according to the third embodiment differs from the second embodiment in that the feed circuit 314 is arranged below the bottom of the cavity 313 (in the opposite direction to the first direction X1).

[0093] The radiating element 312 is fed by a feed conductor 316 connected to a feed circuit 314. The feed conductor 316 is, for example, a balanced two-wire feed line having a first feed conductor 3161 and a second feed conductor 3162. A coaxial connector 315 is provided on the side of the cavity 313, and the coaxial connector 315 is connected to the feed circuit 314.

[0094] For details, connect as follows: The thin cavity-equipped antenna 31 further includes a coaxial connector 315 provided on a side of the cavity 313. The feed circuit 314 is provided on the opposite side of the bottom of the cavity 313 in the first direction X1. One end of the first conductor 3141 and one end near the center of the spiral shape of the first element 3121 of the radiating element 312 are connected via a first feed conductor 3161. One end of the second conductor 3142 and one end near the center of the spiral shape of the second element 3122 are connected via a second feed conductor 3162. The other end of the first conductor 3141 is connected to the core wire of the coaxial connector 315. The other end of the second conductor 3142 is connected to the ground of the coaxial connector 315.

[0095] The configuration of the cavity 313 as described above can reduce the length (height) in the first direction X1 compared to the configuration of the cavity 213 (see FIG. 13B), and the simple structure does not complicate the manufacturing process. As a result, the thin-type cavity-equipped antenna 31 can be manufactured at a lower cost compared to the thin-type cavity-equipped antenna 21.

[0096] [Embodiment 4] FIG. 15A is a plan view illustrating an example of a thin cavity-equipped antenna according to the fourth embodiment and a perspective view illustrating a cavity. FIG. 15A shows an example in which the shape of the cavity when viewed from the first direction X1 is square. FIG. 15B is a plan view illustrating the thin cavity-equipped antenna according to the fourth embodiment and a perspective view illustrating the cavity. FIG. 15B shows an example in which the shape of the cavity when viewed from the first direction X1 is a regular hexagon.

[0097] 15A and 15B, in the thin cavity-equipped antenna 41 according to the fourth embodiment, the shape of the radiating element 412 as viewed from the first direction X1 is a spiral or helical shape. Also, the shape of the cavity 413 as viewed from the first direction X1 is a polygonal shape. Note that the shape of the cavity 413 as viewed from the first direction X1 may be a circular shape or an approximately circular shape, as shown in FIG.

[0098] The advantage of the cavity-fitted antenna according to the embodiment is that it has a thin cavity. Since the thin cavity-fitted antenna 41 has such a shape, it can obtain the same effects as the thin cavity-fitted antenna 11 according to the first embodiment.

[0099] <Radiating element> FIG. 16A is a perspective view illustrating a radiating element and a perspective view illustrating a thin cavity-equipped antenna according to the fourth embodiment. FIG. 16B is a perspective view illustrating a radiating element and a perspective view illustrating a thin cavity-equipped antenna according to the fourth embodiment.

[0100] Figures 16A and 16B show several types of radiating elements that can be used. In addition to the spiral antenna with a helical (spiral) copper foil pattern shown in Figure 1, radiating elements of a wide variety of shapes can be used as long as they are roughly flat.

[0101] Fig. 16A(a) is an example in which a sinusoidal antenna is used. Fig. 16A(b) is an example in which a sinusoidal antenna is placed in a cavity. The radiating element according to the fourth embodiment is not limited to a spiral antenna.

[0102] Fig. 16A(c) is an example using a dipole antenna. Fig. 16A(d) is an example where a dipole antenna is placed in a cavity. That is, radiating element 412 may be a dipole antenna having a first element extending in the direction opposite to second direction X2 and a second element extending in second direction X2.

[0103] A dipole antenna is not a wideband antenna. A dipole antenna can be used with a length that is an integer multiple of (1 / 2) wavelength. When a dipole antenna is used as a unidirectional antenna in a multiband environment, the cavity-equipped shape of the present disclosure is effective.

[0104] Figure 16B (a) shows an example using a cross dipole antenna. Figure 16B (b) shows an example in which a cross dipole antenna is placed in a cavity. That is, radiating element 412 is a cross dipole antenna that, in addition to the first element and second element shown in Figure 16A (c), further includes a third element extending in a third direction X3 that is orthogonal to first direction X1 and orthogonal to second direction X2, and a fourth element extending in the direction opposite to third direction X3.

[0105] (c) of Fig. 16B is an example in which a loop antenna is used. (d) of Fig. 16B is an example in which a loop antenna is placed in a cavity. That is, radiating element 412 is a loop antenna in a substantially circular ring shape when viewed from first direction X1. Both antennas have a flat (planar) shape and can be used in multiple bands.

[0106] Radiating elements that can be used in addition to the antennas described above include bowtie antennas, slot antennas, cross slot antennas, slot loop antennas, and spiral slot antennas. Spiral antennas include Archimedes spiral antennas and equiangular spiral antennas.

[0107] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention.

[0108] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. (Appendix 1) a printed circuit board having a first surface perpendicular to a first direction; a radiating element provided on a first surface of the printed circuit board, the radiating element being made of a conductor and radiating radio waves in the first direction; a cavity provided on the opposite side of the radiating element from the first direction, the cavity being made of a conductor and having a concave shape in the opposite direction from the first direction; a feeding circuit for feeding the radiating element; Equipped with a first length of the cavity in the first direction is equal to or less than one-tenth of a second length of the cavity in a second direction perpendicular to the first direction; Thin cavity antenna. (Appendix 2) The radiating element is a first element provided as a conductor pattern on a first surface of the printed circuit board and having a spiral shape when viewed from the first direction; a second element provided as a separate conductor pattern on the first surface of the printed circuit board, the second element forming a pair of spiral shapes with the first element when viewed from the first direction; and a portion of the second element is disposed between a portion of the first element and another portion of the first element; 10. The low-profile cavity-backed antenna of claim 1. (Appendix 3) The power supply circuit includes: a dielectric layer made of a dielectric material; a first conductor provided on a first surface of the dielectric layer and made of a conductor; a second conductor provided on a second surface of the dielectric layer and made of a conductor; and one end of the first conductor is connected to one end of the first element that is close to the center of the spiral shape, A high frequency signal is connected to the other end of the first conductor, one end of the second conductor is connected to one end of the second element that is close to the center of the spiral shape, The other end of the second conductor is connected to a ground. a length of the second conductor in a third direction increases from one end of the second conductor to the other end of the second conductor, The third direction is a direction perpendicular to the first direction and the second direction. 2. A low-profile cavity-backed antenna as described in Appendix 2. (Appendix 4) The cavity is a bottom portion having a plane perpendicular to the first direction; a side surface portion extending in the first direction from a peripheral portion of the bottom portion; having 10. The low-profile cavity-backed antenna according to claim 3. (Appendix 5) a coaxial connector disposed at the bottom of the cavity; the other end of the first conductor is connected to a core wire of the coaxial connector, The other end of the second conductor is connected to the ground of the coaxial connector. 5. A low-profile cavity-backed antenna as described in Appendix 4. (Appendix 6) The length of the power supply circuit in the first direction is longer than a predetermined length. 10. The low-profile cavity-backed antenna according to claim 3. (Appendix 7) The cavity is a first portion having a length in the second direction longer than a length in the second direction of the printed circuit board; a second portion having a length in the second direction that is shorter than a length in the second direction of the printed circuit board; and The length of the power supply circuit in the first direction is longer than the length of the second portion in the first direction. 10. The low-profile cavity-backed antenna according to claim 3. (Appendix 8) a coaxial connector provided on the side surface of the cavity; the power supply circuit is provided on the opposite side of the bottom of the cavity in the first direction, one end of the first conductor and one end of the first element close to the center of the spiral shape are connected via a first power supply conductor; one end of the second conductor and one end of the second element close to the center of the spiral shape are connected via a second feed conductor; the other end of the first conductor is connected to a core wire of the coaxial connector, The other end of the second conductor is connected to the ground of the coaxial connector. 5. A low-profile cavity-backed antenna as described in Appendix 4. (Appendix 9) the shape of the radiating element as viewed from the first direction is a spiral or helical shape, The shape of the cavity as viewed from the first direction is circular, approximately circular, or polygonal. 10. The low-profile cavity-backed antenna of claim 1. (Appendix 10) The radiating element is a first element extending in a direction opposite to the second direction; a second element extending in the second direction; having 10. The low-profile cavity-backed antenna of claim 1. (Appendix 11) The radiating element is a third element extending in a third direction perpendicular to the first direction and perpendicular to the second direction; a fourth element extending in a direction opposite to the third direction; further comprising 11. The low-profile cavity-backed antenna of claim 10. (Appendix 12) The radiating element has a substantially circular ring shape when viewed from the first direction. 10. The low-profile cavity-backed antenna of claim 1. [Explanation of symbols]

[0109] 11...Thin cavity antenna 111...Printed circuit board 112...Radiating element 1121...first element 1122...Second element 113...cavity 1131…Bottom 1132…Side part 114...Power supply circuit 1141...First conductor 1142...Second conductor 1143...Dielectric layer 115...Coaxial connector Ps1: First side of the printed circuit board Ps2: Second side of the printed circuit board Ds1...first surface of the dielectric layer Ds2: Second surface of the dielectric layer Pd: Length of the printed circuit board in the second direction Sd: Outermost diameter of spiral element L1...First length L2: Second length X1…first direction X2…Second direction X3…Third direction R…radius R О …initial radius θ...Rotation angle λ1, λ2, λ3, λ6, λ L …wavelength

Claims

1. a printed circuit board having a first surface perpendicular to a first direction; a radiating element provided on a first surface of the printed circuit board, the radiating element being made of a conductor and radiating radio waves in the first direction; a cavity provided on the opposite side of the radiating element from the first direction, the cavity being made of a conductor and having a concave shape in the opposite direction from the first direction; a feeding circuit for feeding the radiating element; Equipped with The radiating element is a first element provided as a conductor pattern on a first surface of the printed circuit board and having a spiral shape when viewed from the first direction; a second element provided as another conductor pattern on the first surface of the printed circuit board, the second element forming a pair of spiral shapes with the first element when viewed from the first direction; and a portion of the second element is disposed between a portion and another portion of the first element; Thin cavity antenna.

2. The power supply circuit includes: a dielectric layer made of a dielectric material; a first conductor provided on a first surface of the dielectric layer and made of a conductor; a second conductor provided on a second surface of the dielectric layer and made of a conductor; and one end of the first conductor is connected to one end of the first element that is close to the center of the spiral shape, A high frequency signal is connected to the other end of the first conductor, one end of the second conductor is connected to one end of the second element that is close to the center of the spiral shape, The other end of the second conductor is connected to a ground. a length of the second conductor in a third direction increases from one end of the second conductor to the other end of the second conductor, the third direction is a direction perpendicular to the first direction and the second direction, The second direction is a direction perpendicular to the first direction.

2. The low-profile cavity-equipped antenna according to claim 1.

3. The cavity is a bottom portion having a plane perpendicular to the first direction; a side surface portion extending in the first direction from a peripheral portion of the bottom portion; having 3. The thin cavity antenna according to claim 2.

4. a coaxial connector disposed at the bottom of the cavity; the other end of the first conductor is connected to a core wire of the coaxial connector, The other end of the second conductor is connected to the ground of the coaxial connector.

4. The thin cavity antenna according to claim 3.

5. The cavity is a first portion having a length in the second direction that is longer than a length in the second direction of the printed circuit board; a second portion having a length in the second direction that is shorter than a length in the second direction of the printed circuit board; and a length of the power supply circuit in the first direction is longer than a length of the second portion in the first direction; 4. The thin cavity antenna according to claim 3.

6. a coaxial connector provided on the side surface of the cavity; the power supply circuit is provided on the opposite side of the bottom of the cavity in the first direction, one end of the first conductor and one end of the first element close to the center of the spiral shape are connected via a first power supply conductor; one end of the second conductor and one end of the second element close to the center of the spiral shape are connected via a second power supply conductor; the other end of the first conductor is connected to a core wire of the coaxial connector, The other end of the second conductor is connected to the ground of the coaxial connector.

4. The thin cavity antenna according to claim 3.

7. a printed circuit board having a first surface perpendicular to a first direction; a radiating element provided on a first surface of the printed circuit board, the radiating element being made of a conductor and radiating radio waves in the first direction; a cavity provided on the opposite side of the radiating element from the first direction, the cavity being made of a conductor and having a concave shape in the opposite direction from the first direction; a feeding circuit for feeding the radiating element; Equipped with the shape of the radiating element as viewed from the first direction is a spiral or helical shape, The shape of the cavity as viewed from the first direction is circular, approximately circular, or polygonal. Thin cavity antenna.

8. a printed circuit board having a first surface perpendicular to a first direction; a radiating element provided on a first surface of the printed circuit board, the radiating element being made of a conductor and radiating radio waves in the first direction; a cavity provided on the opposite side of the radiating element from the first direction, the cavity being made of a conductor and having a concave shape in the opposite direction from the first direction; a feeding circuit for feeding the radiating element; Equipped with the second direction is a direction perpendicular to the first direction, The radiating element is a first element extending in a direction opposite to the second direction; a second element extending in the second direction; having Thin cavity antenna.

9. a printed circuit board having a first surface perpendicular to a first direction; a radiating element provided on a first surface of the printed circuit board, the radiating element being made of a conductor and radiating radio waves in the first direction; a cavity provided on the opposite side of the radiating element from the first direction, the cavity being made of a conductor and having a concave shape in the opposite direction from the first direction; a feeding circuit for feeding the radiating element; Equipped with The radiating element has a substantially circular ring shape when viewed from the first direction. Thin cavity antenna.

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