Circularly polarized antenna device

Abstract

This circularly polarized antenna device is provided with: element antennas (10) that emit circularly polarized waves; and a space matching layer (200) that is disposed in firm contact with the surface of the element antennas (10) on the side that emits radio waves, and that has a thickness such that the phase shift amount of the radio waves that are incident by being radiated from the element antennas (10) at a specific scanning angle is in the range from 75 degrees to 105 degrees.

Description

Circularly polarized antenna device

[0001] The present disclosure relates to a circularly polarized antenna device having element antennas.

[0002] In a phased array antenna in which multiple element antennas are arranged and the excitation phase of each element antenna can be electronically changed to direct the main beam in any direction, Patent Document 1 proposes an antenna that prevents a decrease in operating gain due to deterioration of the active reflection coefficient, which is the reflection coefficient when the element antennas are operating at a wide angle when scanned at a wide angle.

[0003] The antenna shown in Patent Document 1 comprises an aperture having a plurality of element antennas operable to radiate radio frequency (RF) energy, and a single-layer Wide Angle Impedance Matching (WAIM) structure coupled to the aperture to provide impedance matching between the aperture and free space, the WAIM structure being an antenna that is a capacitive patch separated from the aperture by a dielectric spacer or foam.

[0004] Special Publication No. 2023-526456

[0005] Since the antenna device disclosed in Patent Document 1 is configured as described above, the wider the incident angle of the radio waves radiated from the element antennas with respect to the capacitive patch constituting the WAIM structure, the greater the difference in passing phase between the TE (Transverse Electric) waves and the TM (Transverse Magnetic) waves. In the antenna device disclosed in Patent Document 1, if the element antenna is configured to radiate circularly polarized waves, the wider the scanning angle of the radio wave radiation direction, the greater the difference in passing phase between the TE waves and the TM waves, resulting in a problem of deterioration of the axial ratio characteristics.

[0006] The present disclosure has been made in consideration of the above points, and aims to provide a circularly polarized antenna device that prevents a decrease in operating gain due to deterioration of the active reflection coefficient during wide-angle scanning, and that can obtain good axial ratio characteristics for circularly polarized radio waves.

[0007] The circularly polarized antenna device according to the present disclosure comprises an element antenna that radiates circularly polarized waves, and a spatial matching layer that is arranged in close proximity to the surface of the element antenna that radiates radio waves and has a thickness such that the phase shift of the radio waves radiated from the element antenna at a specific scanning angle and incident thereon is in the range of 75 degrees to 105 degrees.

[0008] According to the present disclosure, the spatial matching layer prevents a decrease in operating gain due to deterioration of the active reflection coefficient in wide-angle scanning, and since the spatial matching layer does not cause a phase difference between the passing TE waves and TM waves, good axial ratio characteristics are obtained for circularly polarized radio waves.

[0009] 1 is a perspective view of the antenna device according to embodiment 1, showing the spatial matching layer and the second dielectric substrate; FIG. 2 is a top view of an element antenna in the antenna device according to embodiment 1, showing the spatial matching layer and the second dielectric substrate; FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2; FIG. 4 is an equivalent circuit diagram of the spatial matching layer in the antenna device according to embodiment 1; FIG. 5 is a diagram showing the relationship between the relative dielectric constant and the passing amplitude in the antenna device according to embodiment 1; FIG. 6 is a diagram showing the relationship between the amount of phase shift and the passing amplitude in the antenna device according to embodiment 1; FIG. 7 is a diagram showing the relationship between the amount of phase shift and the passing phase difference of the TE wave and the TM wave in the antenna device according to embodiment 1; FIG. 8 is a top view of the spatial matching layer in the antenna device according to embodiment 2; and FIG. 9 is a side view of the spatial matching layer in the antenna device according to embodiment 3.

[0010] Embodiment 1 A circularly polarized antenna device according to embodiment 1 will be described with reference to Figures 1 to 7. The circularly polarized antenna device according to embodiment 1 is a circularly polarized antenna device including an antenna substrate 100, which is a phased array antenna in which a plurality of element antennas 10 are arranged and which emits circularly polarized waves, and a spatial matching layer 200.

[0011] 1, the antenna substrate 100 constitutes an array antenna having a plurality of element antennas 10 arranged two-dimensionally in the X and Y directions, and includes a first dielectric substrate 1, a second dielectric substrate 2, a cavity 3 having a hollow structure 3a at the position where each of the plurality of element antennas 10 is formed, and a base plate (ground layer) 4. The antenna substrate 100 is a passive patch antenna having the hollow structure 3a.

[0012] That is, the array antenna comprises a first dielectric substrate 1 and a second dielectric substrate 2 arranged opposite each other, a cavity 3 sandwiched between the first dielectric substrate 1 and the second dielectric substrate 2 and having a plurality of hollow structures 3a, and a plurality of element antennas 10 are passive patch element antennas formed in the hollow structures 3a in the cavity 3.

[0013] The first dielectric substrate 1 is attached to the lower surface of the cavity 3, and the second dielectric substrate 2 is attached to the upper surface of the cavity 3. In the hollow structure 3a of the cavity 3, the first dielectric substrate 1, the second dielectric substrate 2, and the cavity 3 form a hollow portion. The cavity 3 is a dielectric substrate whose entire surface is metal-plated. The ground plane 4 is a metal layer attached to the lower surface of the first dielectric substrate 1.

[0014] As shown in Figures 2 and 3, each element antenna 10 located in the hollow structure 3a in the cavity 3 is composed of a first dielectric substrate 1, a second dielectric substrate 2, the hollow structure 3a in the cavity 3, a ground plane 4, an excited patch element (antenna element) 11, and a parasitic patch (parasitic element) 12. The element antenna 10 is a patch element antenna with a parasitic element. The element antenna 10 is a patch element antenna having a hollow structure 3a.

[0015] The excited patch element 11 has a patch section 11a, a first feeding point 11b, and a second feeding point 11c. The patch section 11a is formed by a conductor pattern on the upper surface of the first dielectric substrate 1. The first feeding point 11b and the second feeding point 11c are each formed on the lower surface of the first dielectric substrate 1, spaced apart from the ground plane 4 and electrically insulated from the ground plane 4. The first feeding point 11b and the second feeding point 11c are each electrically connected to the patch section 11a via a through hole.

[0016] Radio frequency (RF) signals with electronically controlled excitation phases are input to the first feed point 11b and the second feed point 11c, respectively, and circularly polarized radio waves consisting of TE and TM plane waves are emitted from the patch unit 11a. RF signals with equal amplitude and a 90° phase difference are fed to the first feed point 11b and the second feed point 11c, and radio waves based on the RF signals with circular polarization characteristics are generated from the patch unit 11a.

[0017] The non-excited patch 12 is formed of a conductor pattern on the lower surface of the second dielectric substrate 2, facing the patch portion 11a of the excited patch element 11. When power is supplied to the excited patch element 11, a current is also excited in the non-excited patch 12, which is electromagnetically coupled to the patch portion 11a of the excited patch element 11.

[0018] The spatial matching layer 200 is disposed in close contact with the surface of the element antennas 10 on the side that emits radio waves. That is, the spatial matching layer 200 is disposed in close contact with the surface of the antenna substrate 100, which is an array antenna, on the side that emits radio waves from a plurality of element antennas 10. In the first embodiment, the spatial matching layer 200 is adhered to the upper surface of the second dielectric substrate 2 that constitutes the antenna substrate 100 by prepreg. Note that the spatial matching layer 200 may be attached to the antenna substrate 100 by screws while in close contact with the upper surface of the second dielectric substrate 2.

[0019] The spatial matching layer 200 has a thickness such that the amount of phase shift of radio waves passing through the spatial matching layer 200 is in the range of 75 degrees to 105 degrees at a specific scanning angle. In the first embodiment, the thickness is set to be such that the amount of phase shift of radio waves is 90 degrees. The specific scanning angle is, for example, the maximum scanning angle of the coverage area of ​​the antenna device. In the following description, the specific scanning angle at which radio waves are emitted from the element antenna 10 is referred to as a specific direction.

[0020] The spatial matching layer 200 is made of a medium with a relative dielectric constant that makes the passing amplitudes of two orthogonal linearly polarized wave components of radio waves incident from a specific direction of the element antenna 10, i.e., the TE wave and the TM wave, equal. The spatial matching layer 200 is a dielectric with a relative dielectric constant of 1.7 or less. By using a dielectric with a low relative dielectric constant of 1.7 or less as the spatial matching layer 200, it is possible to eliminate the occurrence of the scan blindness phenomenon, in which the active coefficient deteriorates due to surface waves on the spatial matching layer 200 caused by radio waves from the element antenna 10.

[0021] Preferably, the spatial matching layer 200 is a dielectric material with a relative dielectric constant of 1.05 to 1.35, more preferably 1.05 to 1.15. In the first embodiment, the spatial matching layer 200 is a hard foam material with a dielectric constant of 1.1. The spatial matching layer 200 is thicker than ¼ of the guide wavelength of the operating frequency.

[0022] The spatial matching layer 200 will be described in more detail. The relative dielectric constant of the dielectric material constituting the spatial matching layer 200 is ε ｒ When the incident angle (specific scanning angle) of the radio wave from the element antenna 10 to the spatial matching layer 200 is θ, the propagation constant β of the electromagnetic wave component propagating in the z direction shown in FIGS. 1 to 3 in the dielectric, i.e., in the forward direction relative to the element antenna 10, is ｉ is expressed by the following equation (1).

[0023] In the above formula (1), β ｉ ＴＥ is the propagation constant of the TE wave, β ｉ ＴＭ is the propagation constant of the TM wave, and the propagation constant of the TE wave is β ｉ ＴＥ and the propagation constant of the TM wave, β ｉＴＭ will have equal values.

[0024] The thickness t of the dielectric material constituting the spatial matching layer 200 is proportional to the phase shift amount β of the radio wave propagating through the spatial matching layer 200. ｉ t [rad.], the thickness t of the dielectric material for which the phase shift is 90 degrees is expressed by the following equation (2).

[0025] In the above equation (2), λ is the guide wavelength of the operating frequency, which is the wavelength of the radio wave emitted from the element antenna 10 .

[0026] As can be seen from the above formula (2), by making the thickness t of the spatial matching layer 200 thicker than ¼ of the guide wavelength λ of the operating frequency, it is possible to apply this to the case where the scanning angle θ is made wide.

[0027] In a specific direction (specific scanning angle), the relative dielectric constant of the dielectric material constituting the spatial matching layer 200 is set to a value such that the passing amplitudes of the TE wave and the TM wave are equal. The wave impedance Z of the TE wave, which is an electromagnetic wave component propagating in the z direction through the dielectric material constituting the spatial matching layer 200, is ｉ ＴＥ and the wave impedance Z of the TM wave ｉ ＴＭ are respectively expressed by the following equations (3) and (4).

[0028]

[0029] In the above formulas (3) and (4), z ０ is the characteristic impedance of free space, which is 120π. Since the spatial matching layer 200 is a dielectric layer, it can be expressed as a transmission line as an equivalent circuit, as shown in Figure 4. Therefore, the F matrix F in the spatial matching layer 200 is ｉ ＴＥ／ＴＭ is expressed by the following equation (5).

[0030]

[0031] In free space, the wave impedance of the TE / TM wave of the electromagnetic wave component propagating in the z direction is Z ０ ＴＥ／ＴＭ, the element antenna impedance for TE / TM waves based on the connection surface with the spatial matching layer 200 is Z ａｎｔ ＴＥ／ＴＭ Then, from the above equation (5), the transmission coefficient T ＴＥ／ＴＭ is expressed by the following equation (6).

[0032]

[0033] In free space, the wave impedance Z of a TE wave at an incident angle (specific scanning angle) θ is ０ ＴＥ and the wave impedance Z of the TM wave ０ ＴＭ are expressed by the following equations (7) and (8), respectively.

[0034]

[0035] Fig. 5 shows the relationship between the relative permittivity and the passing amplitude in the dielectric that constitutes the spatial matching layer 200. In Fig. 5, the horizontal axis represents the relative permittivity of the dielectric that constitutes the spatial matching layer 200, the vertical axis represents the passing amplitude in the dielectric, the solid line TE represents the relationship between the passing amplitude and the relative permittivity for the TE wave, the dashed line TM represents the relationship between the passing amplitude and the relative permittivity for the TM wave, and the dashed line TE+TM represents the relationship between the passing amplitude and the relative permittivity for the TEM wave.

[0036] FIG. 5 shows the element antenna impedance Z for TE waves when the scanning angle θ is 70 degrees. ａｎｔ ＴＥ is 300Ω, and the element antenna impedance Z ａｎｔ ＴＭ is set to 100Ω, and the phase shift amount of the spatial matching layer 200 is set to the thickness condition β ｉ This is an example where the calculation is performed assuming t = π / 4 [rad.]. As is clear from Figure 5, the relative dielectric constant of a dielectric that allows the TE wave and TM wave to pass through at equal amplitudes is 1.1. A hard foam is an example of a dielectric that has a relative dielectric constant of 1.1. Therefore, it is preferable to construct the spatial matching layer 200 from a hard foam.

[0037] As is clear from FIG. 5, it is most preferable to use a dielectric material with a relative dielectric constant of 1.1 for the spatial matching layer 200. However, if the relative dielectric constant is 1.05 to 1.15, the passing amplitudes of the TE wave and the TM wave are approximately the same, so there is no particular problem with using a dielectric material with a relative dielectric constant of 1.05 to 1.15 as the spatial matching layer 200 even for wide-angle scanning.

[0038] In addition, when the scanning angle θ is 70 degrees, the element antenna impedance Z ａｎｔ ＴＥ is 200Ω, and the element antenna impedance Z ａｎｔ ＴＭ The phase shift amount of the spatial matching layer 200 is changed to 200Ω under the thickness condition β ｉ As a result of calculation assuming t=π / 4 [rad.], the relative dielectric constant of the dielectric that allows the TE wave and the TM wave to pass through at the same amplitude is 1.35. In other words, a dielectric having a relative dielectric constant of 1.35 or less can be used as the spatial matching layer 200.

[0039] Taking these factors into consideration, an appropriate relative permittivity for the dielectric to be used as the spatial matching layer 200 was investigated, and it was found that, when the spacing between the element antennas 10 is 0.47 wavelengths at the high-frequency end of the operating frequency and the scan angle θ is 75 degrees, by using a dielectric having a low relative permittivity of 1.7 or less as the spatial matching layer 200, it is possible to eliminate the occurrence of the scan blindness phenomenon in which the active coefficient deteriorates due to surface waves on the spatial matching layer 200 caused by radio waves from the element antennas 10. In other words, it is preferable to use a dielectric having a low relative permittivity of 1.7 or less as the spatial matching layer 200.

[0040] Furthermore, the transmission phase ∠T ＴＥ／ＴＭ is the transmission coefficient T of the spatial matching layer 200 shown in the above equation (6). ＴＥ／ＴＭ is expressed by the following equation (9).

[0041]

[0042] As can be seen from the above equation (9), the thickness of the spatial matching layer 200 is set to a value that results in a phase shift of 90 degrees, so that the wave impedance Z in free space at the scanning angle θ is ０ ＴＥ／ＴＭand element antenna impedance Z in TE / TM waves ａｎｔ ＴＥ／ＴＭ Regardless of the value of , the passing phase in the spatial matching layer 200 is 90 degrees, and no passing phase difference occurs between the TE wave and the TM wave. Therefore, no deterioration in the axial ratio characteristics of circularly polarized waves due to the passing phase difference between the TE wave and the TM wave occurs, and good axial ratio characteristics can be obtained.

[0043] Next, we will explain the amount of phase shift, that is, the thickness of the spatial matching layer 200. Radio waves emitted from the antenna substrate 100, that is, radio waves emitted from the multiple element antennas 10, are radiated into space via the spatial matching layer 200. At this time, the spatial matching layer 200 has a thickness that causes a phase shift of 90 degrees for the radio waves passing through it, so the spatial matching layer 200 operates as a matching circuit for a quarter-wave impedance line (transmission line), as shown in the equivalent circuit of FIG.

[0044] Therefore, the spatial matching layer 200 improves the passing amplitude of the radio waves emitted from the element antenna 10 compared to when the radio waves are directly emitted into free space. In other words, the spatial matching layer 200 improves the matching between the element antenna 10 and free space, and improves the reduction in operating gain due to the deterioration of the active reflection coefficient.

[0045] The relationship between the passing amplitude and the passing phase difference was examined by changing the thickness of the spatial matching layer 200, i.e., the amount of phase shift. Figure 6 shows the relationship between the passing amplitude and the amount of phase shift in the spatial matching layer 200. In Figure 6, the horizontal axis represents the amount of phase shift in the spatial matching layer 200, the vertical axis represents the passing amplitude in the spatial matching layer 200, the solid line TE represents the relationship between the passing amplitude and the amount of phase shift for the TE wave, the dashed line TM represents the relationship between the passing amplitude and the amount of phase shift for the TM wave, and the dashed line TE+TM represents the relationship between the passing amplitude and the amount of phase shift for the TEM wave.

[0046] 7 shows the relationship between the amount of phase shift in the spatial matching layer 200 and the passing phase difference between the TE wave and the TM wave. In FIG. 7, the horizontal axis represents the amount of phase shift in the spatial matching layer 200, and the vertical axis represents the passing phase difference between the TE wave and the TM wave.

[0047] 6 and 7 show the element antenna impedance Z for TE waves when the scanning angle θ is 70 degrees.ａｎｔ ＴＥ is 300Ω, and the element antenna impedance Z ａｎｔ ＴＭ This is an example where the calculation is performed assuming that the resistance is 100Ω.

[0048] As is clear from Figures 6 and 7, the thickness of the spatial matching layer 200 is most preferably a thickness that results in a phase shift of 90 degrees for the radio waves that pass through it. If the phase shift of the radio waves that pass through is in the range of 75 degrees to 105 degrees, the difference in the passing amplitude between the TE wave and the TM wave is small, and the passing phase difference between the TE wave and the TM wave is also small, so there is no risk of the axial ratio characteristics deteriorating even in wide-angle scanning.

[0049] Next, the operation of the circularly polarized antenna device according to embodiment 1 will be described. Each of the multiple element antennas 10 on the antenna substrate 100 is excited with a phase difference so that the beam is directed at the scanning angle θ. In each element antenna 10, RF signals with equal amplitude and a phase difference of 90 degrees are input to the first feed point 11b and the second feed point 11c of the excited patch element 11, and the patch section 11a of the excited patch element 11 is fed with equal amplitude and a phase difference of 90 degrees by the first feed point 11b and the second feed point 11c.

[0050] The patch section 11a of the excited patch element 11 is fed with equal amplitude and a 90-degree phase difference from the first feed point 11b and the second feed point 11c, thereby emitting radio waves with circular polarization characteristics. Furthermore, when the patch section 11a is fed with power, a current is also excited in the non-excited patch 12 that is electromagnetically coupled to the patch section 11a.

[0051] The radio wave having circular polarization characteristics emitted from the patch portion 11a is radiated into free space via the spatial matching layer 200.

[0052] The circularly polarized antenna device of embodiment 1 is arranged in close proximity to the surface of the radio wave emitting side of the element antenna 10 that radiates circularly polarized waves, and is provided with a spatial matching layer of a thickness such that the phase shift of the radio waves radiated from the element antenna 10 at a specific scanning angle and incident thereon is in the range of 75 degrees to 105 degrees.Therefore, it is easy to manufacture, prevents a decrease in gain during wide-angle scanning, and achieves good axial ratio characteristics.

[0053] The circularly polarized antenna device according to the first embodiment can prevent degradation of the axial ratio characteristics during wide-angle scanning because no passing phase difference occurs between the TE wave and the TM wave during wide-angle scanning, regardless of the wave impedance of free space, the relative dielectric constant of the medium of the spatial matching layer 200, and the impedance of the element antenna 10. In the circularly polarized antenna device according to the first embodiment, the spatial matching layer 200 operates like a quarter-wave impedance line in circuit theory, so that even during wide-angle scanning, the matching between free space and the element antenna 10 is improved, and reduction in operating gain due to deterioration of the active reflection coefficient can be improved.

[0054] The circularly polarized antenna device according to the first embodiment can obtain good axial ratio characteristics even in wide-angle scanning because the spatial matching layer 200 is made of a medium with a relative dielectric constant that equalizes the passing amplitudes of two orthogonal linearly polarized components of radio waves incident from a specific scanning angle of the element antenna 10. The circularly polarized antenna device according to the first embodiment can prevent degradation of the axial ratio characteristics even in wide-angle scanning by using a dielectric material as the spatial matching layer 200 with a low relative dielectric constant of 1.7 or less, preferably a dielectric material with a relative dielectric constant of 1.05 to 1.35, and more preferably a dielectric constant of 1.05 to 1.15. This makes it possible to prevent degradation of the axial ratio characteristics even in wide-angle scanning because the passing amplitudes of the TE wave and the TM wave are approximately the same.

[0055] In the circularly polarized antenna device according to embodiment 1, by selecting a dielectric having a low relative permittivity of 1.7 or less as the spatial matching layer 200, in particular a medium having a low permittivity such as hard foam as the spatial matching layer 200, it is possible to alleviate the condition for the maximum element spacing that causes the scan blindness phenomenon in the visible range, in which the active coefficient is significantly degraded at certain scanning angles due to surface waves emitted from the antenna substrate 100.

[0056] Although a parasitic patch antenna having a hollow structure 3a has been described as the antenna substrate 100, a tightly coupled dipole, a tapered slot antenna, a bowtie antenna, or a patch antenna without a hollow structure may also be used.

[0057] Furthermore, the spatial matching layer 200 has been mainly described as being made of a dielectric material having a relative dielectric constant of 1.05 to 1.15. However, the element antenna impedance Z ａｎｔ ＴＥ／ＴＭ In some cases, the dielectric may have a relative permittivity outside the above range.

[0058] Furthermore, although each element antenna 10 generates circularly polarized wave characteristics using a two-point feed method with the first feed point 11b and the second feed point 11c, a notched patch antenna or a polarizer may also be used. Also, the circularly polarized wave excited (emitted) from the antenna substrate 100 does not have to be a perfect circularly polarized wave with an axial ratio of 0 dB, and may be an elliptically polarized wave.

[0059] Embodiment 2. A circularly polarized antenna device according to embodiment 2 will be described with reference to Figure 8. The circularly polarized antenna device according to embodiment 2 differs from the circularly polarized antenna device according to embodiment 1 in that, as opposed to spatial matching layer 200 in the circularly polarized antenna device according to embodiment 1, spatial matching layer 201 is formed of a dielectric material having a plurality of holes 201a formed therein, but the rest of the configuration is the same. Therefore, the following description will mainly focus on spatial matching layer 201, which is the difference from the circularly polarized antenna device according to embodiment 1.

[0060] The circularly polarized antenna device according to the second embodiment includes an antenna substrate and a spatial matching layer 201. The antenna substrate in the circularly polarized antenna device according to the second embodiment is the same as the antenna substrate 100 in the circularly polarized antenna device according to the first embodiment, and the spatial matching layer 201 is adhered by prepreg in close contact with the upper surface of the second dielectric substrate 2 constituting the antenna substrate 100 shown in the circularly polarized antenna device according to the first embodiment. Therefore, a description of the antenna substrate will be omitted.

[0061] The spatial matching layer 201 is a dielectric material with a plurality of holes 201a two-dimensionally formed therein. The holes 201a penetrate from the upper surface to the lower surface (z direction in FIG. 8) of the spatial matching layer 201. The holes are cylindrical in shape.

[0062] The holes 201a do not have to be cylindrical holes, and the shape of the holes 201a, the direction in which the holes are drilled, and whether or not they penetrate from the top surface to the bottom surface may be selected appropriately for each of the multiple holes 201a. The dielectric material that makes up the spatial matching layer 201 is a hard foam, a fluororesin, or a thermosetting resin.

[0063] The thickness of the spatial matching layer 201 is set so that the phase shift of the radio waves passing through the spatial matching layer 200 is in the range of 75 degrees to 105 degrees at a specific scanning angle. In the second embodiment, the thickness is set so that the phase shift of the radio waves is 90 degrees.

[0064] The equivalent relative permittivity of the spatial matching layer 201 is determined by the number of holes 201a drilled in the dielectric and the size (inner shape) of the holes 201a, and the transmission coefficient T ＴＥ／ＴＭ The spatial matching layer 201 is determined so that the passing amplitude of the spatial matching layer 201 calculated from the above formula is approximately the same for the TE wave and the TM wave. That is, the spatial matching layer 201 is formed of a dielectric material having a plurality of holes 201a formed therein, and the equivalent relative dielectric constant of the spatial matching layer 201 is set to 1.7 or less, preferably 1.05 to 1.35, more preferably 1.05 to 1.15, and most preferably 1.1.

[0065] Next, the operation of the circularly polarized antenna device according to embodiment 2 will be described. The operation of the circularly polarized antenna device according to embodiment 2 is the same as that of the circularly polarized antenna device according to embodiment 1, and each of the multiple element antennas on the antenna substrate is excited with a phase difference so that the beam is directed at the scanning angle θ. Radio waves having circular polarization characteristics emitted from each element antenna are radiated into free space via spatial matching layer 201.

[0066] The circularly polarized antenna device of embodiment 2 has the same effect as the circularly polarized antenna device of embodiment 1. In addition, since the spatial matching layer 201 is made of a dielectric material with a plurality of holes 201a two-dimensionally drilled therein, the equivalent relative dielectric constant of the spatial matching layer 201 can be adjusted by the material of the dielectric material constituting the spatial matching layer 201 and the number and size of the holes 201a, allowing for a highly flexible design.

[0067] Embodiment 3. A circularly polarized antenna device according to embodiment 3 will be described with reference to Figure 9. The circularly polarized antenna device according to embodiment 3 differs from the circularly polarized antenna device according to embodiment 1 in that, unlike spatial matching layer 200 in the circularly polarized antenna device according to embodiment 1, spatial matching layer 202 is formed from a dielectric layer formed by laminating multiple dielectric layers 202a to 202e, but the other points are the same. Therefore, the following description will mainly focus on spatial matching layer 202, which is the difference from the circularly polarized antenna device according to embodiment 1.

[0068] The circularly polarized antenna device according to the third embodiment includes an antenna substrate and a spatial matching layer 202. The antenna substrate in the circularly polarized antenna device according to the third embodiment is the same as the antenna substrate 100 in the circularly polarized antenna device according to the first embodiment, and the spatial matching layer 202 is adhered by prepreg in close contact with the upper surface of the second dielectric substrate 2 constituting the antenna substrate 100 shown in the circularly polarized antenna device according to the first embodiment. Therefore, a description of the antenna substrate will be omitted.

[0069] The spatial matching layer 202 is a dielectric layer formed by laminating a plurality of dielectric layers 202a to 202e, and at least two types of dielectric layers 202a to 202e having different relative dielectric constants are laminated. Each of the plurality of dielectric layers 202a to 202e in the dielectric constituting the spatial matching layer 202 is selected from hard foam, fluororesin, and thermosetting resin.

[0070] The thickness of the spatial matching layer 202 is set so that the phase shift of the radio waves passing through the spatial matching layer 200 is in the range of 75 degrees to 105 degrees at a specific scanning angle. In the third embodiment, the thickness is set so that the phase shift of the radio waves is 90 degrees.

[0071] The equivalent relative permittivity of the spatial matching layer 201 is determined by the relative permittivity of each of the plurality of dielectric layers 202a to 202e and the ratio of their thicknesses, and is expressed by the transmission coefficient T ＴＥ／ＴＭThe spatial matching layer 202 is determined so that the passing amplitude of the spatial matching layer 202 calculated from the above formula (1) is approximately the same for the TE wave and the TM wave. That is, the spatial matching layer 202 is a layered structure of a plurality of dielectric layers 202a to 202e whose equivalent relative permittivity is set to 1.7 or less, preferably 1.05 to 1.35, more preferably 1.05 to 1.15, and most preferably 1.1.

[0072] Next, the operation of the circularly polarized antenna device according to embodiment 3 will be described. The operation of the circularly polarized antenna device according to embodiment 3 is the same as that of the circularly polarized antenna device according to embodiment 1, and each of the multiple element antennas on the antenna substrate is excited with a phase difference so that the beam is directed at the scanning angle θ. Radio waves having circular polarization characteristics emitted from each element antenna are radiated into free space via spatial matching layer 202.

[0073] The circularly polarized antenna device of embodiment 3 has the same effects as the circularly polarized antenna device of embodiment 1. In addition, since the spatial matching layer 202 is made of a dielectric in which a plurality of dielectric layers 202a to 202e are stacked, the equivalent relative dielectric constant of the spatial matching layer 202 can be adjusted by adjusting the relative dielectric constant of each of the plurality of dielectric layers 202a to 202e in the dielectric that makes up the spatial matching layer 201 and the ratio of their respective thicknesses, allowing for a highly flexible design.

[0074] It should be noted that the embodiments may be freely combined, any of the components of the embodiments may be modified, or any of the components of the embodiments may be omitted.

[0075] The circularly polarized antenna device according to the present disclosure is applied to a phased array antenna that radiates circularly polarized waves and is used in a satellite communication system or the like.

[0076] 100 Antenna substrate, 10 Element antenna, 1 First dielectric substrate, 2 Second dielectric substrate, 3 Cavity, 4 Ground plane, 11 Excitation patch element, 11a Patch portion, 11b First feeding point, 11c Second feeding point, 12 Non-excitation patch, 200, 201, 202 Spatial matching layer, 201a Hole.

Claims

1. A circularly polarized antenna device comprising: an element antenna that radiates circularly polarized waves; and a spatial matching layer that is placed in close contact with the surface of the element antenna on the side that radiates radio waves, and that has a thickness such that the amount of phase shift of radio waves radiated from the element antenna at a specific scanning angle and incident thereon is in the range of 75 to 105 degrees.

2. A circularly polarized antenna device comprising: an array antenna having a plurality of element antennas arranged two-dimensionally; and a spatial matching layer arranged in close proximity to the surface of the array antenna from which the plurality of element antennas emit radio waves, the spatial matching layer having a thickness such that the phase shift of the radio waves emitted from each of the plurality of element antennas at a specific scanning angle and incident thereon is 75 to 105 degrees.

3. A circularly polarized antenna device according to claim 2, wherein the array antenna comprises a first dielectric substrate and a second dielectric substrate arranged opposite each other, a cavity having a plurality of hollow structures sandwiched between the first dielectric substrate and the second dielectric substrate, the plurality of element antennas being non-excited patch element antennas formed in the hollow structures in the cavity, and the spatial matching layer is positioned relative to the array antenna in close contact with the upper surface of the second dielectric substrate in the array antenna.

4. A circularly polarized antenna device according to claim 1, wherein said element antenna is a parasitic patch element antenna.

5. A circularly polarized antenna device according to claim 1, wherein said element antenna is a patch element antenna having a hollow structure.

6. A circularly polarized antenna device according to claim 1, wherein said element antennas are tightly coupled dipoles.

7. A circularly polarized antenna device according to any one of claims 1 to 6, wherein the specific scanning angle is the maximum scanning angle of the coverage area of ​​the antenna device.

8. A circularly polarized antenna device as claimed in any one of claims 1 to 7, wherein the spatial matching layer is composed of a medium having a relative dielectric constant such that the passing amplitudes of two orthogonal linearly polarized components of radio waves incident on the element antenna from a specific scanning angle are equal.

9. A circularly polarized antenna device according to any one of claims 1 to 8, wherein the spatial matching layer is a dielectric material having a relative dielectric constant of 1.7 or less.

10. A circularly polarized antenna device according to any one of claims 1 to 9, wherein the spatial matching layer is a foam material.

11. A circularly polarized antenna device according to any one of claims 1 to 10, wherein the thickness of said spatial matching layer is greater than 1 / 4 of the guide wavelength of the operating frequency.

12. A circularly polarized antenna device according to any one of claims 1 to 11, wherein the spatial matching layer is a dielectric material having a plurality of holes two-dimensionally formed therein.

13. A circularly polarized antenna device according to claim 12, wherein the hole formed in the dielectric material constituting the spatial matching layer is a hole drilled through the spatial matching layer from its upper surface to its lower surface.

14. A circularly polarized antenna device according to any one of claims 1 to 11, wherein the spatial matching layer is a dielectric layer formed by laminating a plurality of dielectric layers.

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