Radio wave lens, and antenna device using a radio wave lens

Abstract

This invention provides a radio wave lens that is lightweight, simple in shape and structure, and can efficiently control the radiation directivity of a horn antenna. [Solution] A radio wave lens 1 connected to the aperture surface ap1 of a horn antenna a1 that radiates and / or receives radio waves of a predetermined frequency, wherein the radio wave lens 1 is made of a dielectric material, has a constant cross-sectional shape and size, has a cylindrical structure with a length of 1 to 6 times the free-space wavelength of the radio wave, has an inner cross-sectional shape and size substantially identical to that of the aperture surface ap1 of the horn antenna a1, and the thickness of the side wall of the cylindrical structure substantially identical to the wavelength of the radio wave in the dielectric material.

Description

Technical Field

[0001] The present invention relates to a radio wave lens connected to a horn antenna and narrowing the radiation directivity, and an antenna device using the radio wave lens.

Background Art

[0002] The directivity (half-value width angle) of a horn antenna is determined by the relationship between the shape and size of the horn antenna and the wavelength of the radio wave. When the wavelength of the radio wave to be used is predetermined, in order to enhance the directivity, it is necessary to simultaneously increase the aperture diameter and the antenna length, and there is a problem that the antenna body becomes large.

[0003] Patent Document 1 discloses a dielectric lens for a horn antenna. By attaching a dielectric formed in a lens shape to the opening surface of the horn antenna, the directivity can be enhanced without increasing the size of the horn antenna.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The dielectric lens disclosed in Patent Document 1 has a substantially parabolic lens shape, resulting in a structure where the dielectric is thick in the center and thin at the periphery, making it heavy. Furthermore, when manufactured by molding, where molten dielectric material is injected into a mold, the effect of shrinkage during cooling is significant, making it difficult to improve the finish accuracy after molding. While it is possible to improve the finish accuracy by improving the cooling process or adding machining for finishing, this increases the working time and process, resulting in higher costs. Moreover, because the dielectric is thick, the effect of dielectric loss when radio waves pass through the lens is significant, and in order to avoid this, it is necessary to select a low-loss dielectric, which is a factor that increases manufacturing costs.

[0006] Therefore, the present invention provides a lightweight radio wave lens and an antenna device using a radio wave lens that do not increase the size of the horn antenna and offer a high degree of freedom in material selection. [Means for solving the problem]

[0007] A radio wave lens according to one aspect of the present invention is a radio wave lens connected to the aperture surface of a horn antenna that radiates and / or receives radio waves of a predetermined frequency, and is made of a dielectric material, has a cylindrical structure with a constant cross-sectional shape and size, and a length equal to or greater than the free-space wavelength of the radio wave, wherein the inner shape of the cross-section is substantially the same as the aperture surface of the horn antenna, and the thickness of the side wall of the cylindrical structure is substantially the same as the wavelength of the radio wave in the dielectric material.

[0008] Another aspect of the present invention is an antenna device in which the radio wave lens is connected to a horn antenna. [Effects of the Invention]

[0009] According to the radio wave lens and antenna device using the radio wave lens of the present invention, it is possible to efficiently control the radiation directivity of a horn antenna with a lightweight and simple structure. [Brief explanation of the drawing]

[0010] [Figure 1A]A perspective view showing an example of a radio wave lens and antenna device according to the first embodiment of the present invention. [Figure 1B] Figure 1A is a cross-sectional view of the radio lens and antenna device along the I-I line (XZ plane). [Figure 2A] A diagram illustrating the electric field distribution (H plane) of the antenna device according to the first embodiment of the present invention. [Figure 2B] A diagram illustrating the gain dependence of the antenna device of the first embodiment of the present invention on the directionality angle (H plane). [Figure 3A] A diagram illustrating the electric field distribution (E-plane) of the antenna device according to the first embodiment of the present invention. [Figure 3B] A diagram illustrating the gain dependence of the antenna device of the first embodiment of the present invention on the directionality angle (E-plane). [Figure 4A] A diagram illustrating the electric field distribution (H-plane) of the comparative example antenna device. [Figure 4B] This diagram illustrates the dependence of the gain of the comparative antenna device on the directivity angle (E-plane). [Figure 5A] A perspective view showing a first modified example of the radio wave lens and antenna device according to the first embodiment of the present invention. [Figure 5B] Figure 5A is a cross-sectional view of the radio lens and antenna device along the II-II line (XZ plane). [Figure 6A] A perspective view showing a second modified example of the radio wave lens and antenna device according to the first embodiment of the present invention. [Figure 6B] Figure 6A is a cross-sectional view of the radio lens and antenna device along line III-III (XZ plane). [Figure 7A] A perspective view showing a third modified example of the radio wave lens and antenna device according to the first embodiment of the present invention. [Figure 7B] Figure 7A is a cross-sectional view of the IV-IV line (XZ plane) of the radio lens and antenna device shown. [Figure 8A] This figure illustrates the electric field distribution (H-plane) of an antenna device according to a third modification of the first embodiment of the present invention. [Figure 8B] This figure illustrates the gain dependence on the directional angle (H plane) of an antenna device according to a third modification of the first embodiment of the present invention. [Figure 9A]Perspective view showing an example of a radio wave lens and an antenna device according to a second embodiment of the present invention. [Figure 9B] Cross-sectional view taken along the line V-V (XZ plane) of the radio wave lens and the antenna device shown in FIG. 9A. [Figure 10A] Perspective view showing a modified example of the radio wave lens and the antenna device according to the second embodiment of the present invention. [Figure 10B] Cross-sectional view taken along the line VI-VI (XZ plane) of the radio wave lens and the antenna device shown in FIG. 10A.

Mode for Carrying Out the Invention

[0011] A radio wave lens according to an embodiment and an antenna device using the radio wave lens will be described while referring to the drawings. Note that the radio wave lens and the antenna device shown in the drawings are merely examples of the radio wave lens and the antenna device according to the embodiment. The present invention is not limited to the embodiment shown in the drawings and can be variously modified within the scope of the gist of the present invention. Also, the drawings referred to are drawn so that the features of the present invention can be easily understood, and the sizes and ratios of the respective components may not be accurate.

[0012] FIG. 1A shows a perspective view of a radio wave lens 1, which is an example of a radio wave lens according to the first embodiment, and an antenna device 10 using the radio wave lens 1. FIG. 1B shows a cross-sectional view of the XZ plane taken along the line I-I of FIG. 1A. In FIGS. 1A and 1B, radio waves propagate in the Z-axis direction inside the radio wave lens 1 and the horn antenna a1. Also, assume that the H plane (plane parallel to the magnetic field) is formed in the XZ plane and the E plane (plane parallel to the electric field) is formed in the YZ plane.

[0013] The radio wave lens 1 is formed of a dielectric material and, as shown in Figures 1A and 1B, is mounted on a conical horn antenna a1 having a circular aperture shape to constitute the antenna device 10. The radio wave lens 1 can be formed using any dielectric material, but is preferably made of a resin material, and more preferably of polycarbonate (PC), polyethylene (PE), polypropylene (PP), Teflon (PTFE), etc. These resin materials have a low dielectric constant of about 2 to 3, which can suppress the insertion loss of the radio wave lens 1 with respect to the high-frequency signals transmitted and received by the horn antenna a1. Furthermore, it is desirable that the radio wave lens 1 be made of a uniform material that does not contain fillers, etc. This further suppresses the insertion loss of the radio wave lens 1. Note that these materials are merely examples of materials that easily transmit radio waves, and can be formed from any material that can provide dielectric properties suitable for high-frequency propagation.

[0014] The aperture ap1 of the horn antenna a1 has a circular shape with a diameter d. The radio wave lens 1 has a cylindrical structure with a constant cross-sectional shape and size, a circular cross-sectional shape that is approximately the same as the shape of the aperture ap1 of the horn antenna a1, and side walls that are perpendicular to the aperture ap1. The inner diameter D1 of the cross-section of the radio wave lens 1 is approximately the same as the diameter d of the aperture ap1 of the horn antenna a1. The first end 11 and the second end 12, which are both ends of the radio wave lens 1, are open, and the first end 11 is coupled to the aperture ap1 of the horn antenna a1. The thickness T of the side wall of the radio wave lens 1 is defined as 1 / 2 the distance between the inner diameter D1 and the outer diameter D2 of the cross-section, and is approximately the same as the wavelength λe in the dielectric material of the radio waves radiated or received by the horn antenna a1. That is, the thickness T of the side wall of the radio wave lens 1 satisfies the relationship in Equation 1 for the operating frequency f0 and the relative permittivity εr of the dielectric material forming the radio wave lens. C0 represents the speed of light. T≒C0 / f0 / (εr) 1 / 2 (=λe) Equation 1 The length L of the radio lens 1 should be greater than or equal to the free-space wavelength λ0 of the radio waves transmitted and received by the horn antenna a1, which is represented by Equation 2. λ0=C0 / f0 Equation 2 In other words, by making the length L of the radio lens 1 approximately one wavelength or more, the gain is improved compared to when there is no lens. However, even if the length L is made longer than one wavelength, the effect of further improving the gain is not significant. On the other hand, regarding the directivity characteristics, by making the length L longer than one wavelength, the attenuation pole that appears near the main lobe, especially in the E-plane, becomes larger, and the angle can be narrowed. The frequency of the radio waves transmitted and received by the horn antenna a1 is not particularly limited, but is preferably in the high frequency band of microwaves or higher, and more preferably in the high frequency band of millimeter waves or higher.

[0015] Specific examples of the radio wave lens 1 and antenna device 10 will be explained with reference to Figures 1 to 3. In the radio wave lens 1 and antenna device 10 shown in Figure 1, when radiating radio waves with a frequency of 60 GHz, the diameter d of the aperture surface ap1 of the horn antenna a1 is, for example, about 26 mm. The free-space wavelength λ0 of the radio wave with a frequency of 60 GHz is, from Equation 2, λ0 = about 5 mm, and when the relative permittivity εr = 2.8 of the dielectric constituting the radio wave lens 1, the wavelength of the radio wave inside the radio wave lens 1 is about 3 mm from Equation 1. Therefore, the inner diameter D1 of the radio wave lens 1 is about 26 mm, and the outer diameter D2 is about 32 mm.

[0016] Figures 2A and 2B show an example of the radiation characteristics of the H-plane (XZ-plane) of an antenna device 10 that radiates radio waves at a frequency of 60 GHz. Figure 2A shows the electric field distribution diagram obtained from electromagnetic field simulation, and Figure 2B shows the dependence of the antenna gain measured in the far field on the direction of the beam angle, with the radio lens length L as a parameter (L=0, 10, 20 mm). Here, the H-plane is the plane perpendicular to the electric field of the radio waves transmitted and received by the antenna device 10, and corresponds to the XZ-plane in Figures 1A to 2A. In Figure 2B, the horizontal axis shows the direction of the beam angle (unit: deg) when the direction in front of the horn antenna a1, i.e., the normal direction of the aperture surface ap1, is 0 degrees, and the vertical axis shows the antenna gain (unit: dB). Also in Figure 2B, the thin dashed line shows the case without radio lens 1 (L=0 mm), the solid line shows the case with radio lens 1 length L=10 mm, and the thick dashed line shows the case with radio lens 1 length L=20 mm.

[0017] Figures 3A and 3B show an example of the radiation characteristics of the E-plane (YZ-plane) under the same conditions as in Figures 2A and 2B. Figure 3A shows the electric field distribution diagram, and Figure 3B shows the dependence of the antenna gain on the directivity angle measured in the far field. Here, the E-plane is the plane parallel to the electric field of the radio waves transmitted and received by the antenna device 10, and corresponds to the YZ-plane in Figures 1A to 2A. In Figure 3B, the horizontal axis shows the directivity angle (unit: deg), and the vertical axis shows the antenna gain (unit: dB). Also in Figure 3B, the thin dashed line shows the case without radio lens 1 (L=0mm), the solid line shows the case with radio lens 1 length L=10mm, and the thick dashed line shows the case with radio lens 1 length L=20mm. The shape and size of the horn antenna a1 and radio lens 1 are the same as in Figures 2A and 2B.

[0018] As shown in Figure 2A, the electric field radiated from the radio lens 1 forms an electric field pattern close to a plane wave in the far field, and the electric field broadening dependent on propagation distance is suppressed. Furthermore, in Figure 2B, the horn antenna a1, which has an axisymmetric cross-sectional shape in the H plane, exhibits axisymmetric radiation characteristics even when coupled to the radio lens 1, and the directivity angle at which the antenna gain is maximum coincides with the direction in front of the horn antenna a1 (θ=0deg).

[0019] In Figure 3A, as in Figure 2A, the electric field radiated from the radio lens 1 forms an electric field pattern close to a plane wave in the far field, and the electric field broadening dependent on propagation distance is suppressed. Also in Figure 3B, as in Figure 2B, the horn antenna a1, which has an axisymmetric cross-sectional shape in the E-plane, exhibits axisymmetric radiation characteristics even when coupled to the radio lens 1, and the directivity angle at which the antenna gain is maximum coincides with the direction in front of the horn antenna a1 (θ=0deg).

[0020] Figures 2B and 3B show the dependence of the antenna gain on the H and E planes on the directionality angle when the length L of the radio wave lens 1 is 0 mm (no radio wave lens 1), 10 mm (approximately 2 wavelengths), and 20 mm (approximately 4 wavelengths). It can be seen that the maximum gain for L=10 mm and L=20 mm is about 1 dB higher than when there is no lens (L=0 mm). However, there is almost no difference in the maximum gain for L=10 mm and L=20 mm. This is also true for L=5 mm, indicating that if the radio wave lens 1 has a length L of 5 mm or more, which corresponds to one free-space wavelength, the length L of the radio wave lens 1 does not affect the gain improvement effect.

[0021] On the other hand, regarding the directivity characteristics, the size of the attenuation pole and side lobes appearing near the main lobe differs between the L=10mm and L=20mm cases. That is, the attenuation of the attenuation pole is greater (deeper) in the L=20mm case, resulting in sharper directivity. When radio lens 1 is present, the half-width angle is narrowed from 16 degrees to 12 degrees on the H-plane and from 12 degrees to 8 degrees on the E-plane compared to when radio lens 1 is absent, but there is no significant difference in the half-width angle between the L=10mm and L=20mm cases. On the other hand, the size of the side lobes is larger in the L=20mm case than in the L=10mm case, and if the length L of radio lens 1 is made longer than 20mm, the amount of side lobes will increase even further. In the examples shown in Figures 2B and 3B, the optimal value for the length L of radio lens 1 was L=20mm (equivalent to approximately 4 wavelengths), but this value is not uniquely determined by a single parameter. The optimal length L of the radio lens 1 can vary depending on the characteristics of the horn antenna a1 and its relationship to the lens thickness D, or it can be derived by considering multiple parameters such as the performance required of the antenna device 10, but it can be determined, for example, between 1 and 6 wavelengths.

[0022] Based on the above, the length L of the radio lens can be selected within a range that satisfies Equation 3 and is 6 times or less of the free-space wavelength λ0, taking into consideration the relationship between antenna gain, directivity characteristics (half-width angle), and side lobe amount. L≧λ0(=C0 / f0) Equation 3

[0023] Figure 4A shows, as a comparative example, the electric field distribution diagram of the H-plane measured when a metal cylindrical object, formed to the same shape and size as the radio lens 1, was coupled to the horn antenna a1. Figure 4B shows the dependence of the antenna gain on the directivity angle under the same conditions. In Figure 4A, the electric field is blocked by the side walls of the cylindrical object, while a spherical wave is generated at the upper end, which is the exit of the cylindrical object, and the electric field wavefront expands rapidly with propagation distance. Furthermore, as shown in Figure 4B, there is almost no change in the directivity angle dependence even when the length of the cylindrical object is changed, indicating that no lens effect is obtained.

[0024] In contrast, in Figure 2A above, an electric field is generated outside the side wall of the radio wave lens 1 with approximately the same phase as inside the radio wave lens 1, and the electric field wavefront propagates in the direction of the front of the horn antenna a1 via the second end 12. That is, in Figure 2A, by forming the radio wave lens 1 with a dielectric material having approximately the same thickness as the wavelength of the radio wave, a leakage wave component with approximately the same phase as inside the radio wave lens 1 is generated near the outside of the side wall of the radio wave lens 1. For this reason, it is considered that an effect equivalent to expanding the effective size of the aperture surface at the second end 12 of the radio wave lens 1 is obtained. Thus, the radio wave lens 1 of the first embodiment has a structure that can be easily attached to a conical horn antenna a1, and the radio wave lens 1 and antenna device 10 can increase the antenna gain and narrow the directivity angle with a lightweight and simple structure without increasing the size of the horn antenna a1.

[0025] Figure 5A shows a perspective view of a radio wave lens 1α and antenna device 10α, which are first modified examples of the radio wave lens and antenna device of the first embodiment. Figure 5B shows a cross-sectional view of the XZ plane along line II-II in Figure 5A. In Figures 5A and 5B, radio waves propagate in the Z-axis direction within the radio wave lens 1α and horn antenna a1.

[0026] The radio wave lens 1α can be coupled to the aperture surface ap1 of a conical horn antenna a1, similar to the radio wave lens 1 shown in Figures 1A and 1B. The radio wave lens 1α has a structure, shape, and dimensions similar to the radio wave lens 1, except that the second end 12 is closed by a flat plate-shaped cover portion 13 made of a dielectric material. The thickness of the cover portion 13 is approximately half the wavelength λe of the radio waves transmitted and received by the horn antenna a1 in the dielectric material. This suppresses the occurrence of multiple reflections of radio waves within the cover portion 13 and can reduce the transmission loss of radio waves by the cover portion 13. The cover portion 13 can be formed using any dielectric material, but preferably it is formed from the same material as the dielectric material used to form the sidewall of the radio wave lens 1α.

[0027] Thus, the first modified example of the first embodiment of the radio wave lens 1α and antenna device 10α can be improved in terms of environmental resistance by closing the second end 12 with a half-wave plate, while suppressing the increase in insertion loss due to the radio wave lens 1α and preventing foreign matter from entering the inside of the horn antenna a1.

[0028] Figure 6A shows a perspective view of a radio wave lens 1β and antenna device 10β, which are a second modification of the radio wave lens and antenna device of the first embodiment. Figure 6B shows a cross-sectional view of the XZ plane along line III-III in Figure 6A. In Figures 6A and 6B, radio waves propagate in the Z-axis direction within the radio wave lens 1β and horn antenna a1. The radio wave lens 1β can be coupled to a conical horn antenna a1, similar to the radio wave lens 1 shown in Figures 1A and 1B. The radio wave lens 1β has a structure, shape, and dimensions similar to the radio wave lens 1, except that the radio wave lens 1β is formed integrally with the housing CS that accommodates the entire horn antenna a1.

[0029] Thus, in the second modified example of the first embodiment, the radio wave lens 1β and antenna device 10β are formed integrally with the housing CS that houses the horn antenna a1. This suppresses the increase in insertion loss caused by the radio wave lens 1β, prevents foreign matter from entering or adhering to the inside of the horn antenna a1 or surrounding circuits, and further improves environmental resistance.

[0030] Figure 7A shows a perspective view of a third modified example of the radio wave lens and antenna device of the first embodiment, consisting of a radio wave lens 1γ and an antenna device 10γ. Figure 7B shows a cross-sectional view of the XZ plane along line IV-IV in Figure 7A. In Figures 7A and 7B, radio waves propagate in the Z-axis direction within the radio wave lens 1γ and the horn antenna a2. It is assumed that an H plane is formed on the XZ plane and an E plane is formed on the YZ plane.

[0031] The radio wave lens 1γ can be coupled to the aperture surface ap2 of the conical horn antenna a2, similar to the radio wave lens 1 shown in Figures 1A and 1B. The radio wave lens 1γ has the same structure, shape, and dimensions as the radio wave lens 1. That is, the radio wave lens 1γ has a cylindrical structure with a constant cross-sectional shape and size, a circular cross-sectional shape that is approximately the same as the shape of the aperture surface ap2 of the horn antenna a2, and side walls that are perpendicular to the aperture surface ap2. The inner diameter D1 of the cross-section of the radio wave lens 1γ is approximately the same as the diameter d of the aperture surface ap2 of the horn antenna a2. The first end 11 and the second end 12, which are both ends of the radio wave lens 1γ, are open, and the first end 11 is coupled to the aperture surface ap2 of the horn antenna a2. The thickness T of the side wall of the radio wave lens 1γ is approximately the same as the wavelength λe of the radio waves transmitted and received by the horn antenna a2 in the dielectric material. The length L of the radio wave lens 1γ is greater than or equal to the wavelength λ0 of the radio waves transmitted and received by the horn antenna a2 in air. In other words, the length L of the radio wave lens 1γ satisfies the relationship in Equation 1 with respect to the thickness T of the side wall of the radio wave lens 1γ and the dielectric constant εr of the dielectric material.

[0032] Horn antenna a2 has a conical external shape similar to horn antenna a1, but differs in that a metal partition section as2 is provided inside the horn portion from the opening to the feed end in a direction perpendicular to the XZ plane, resulting in a structure that is divided into two when viewed from the H plane (XZ plane). This two-part structure improves the isolation between the divided antennas of horn antenna a2. In sensors using radio waves, separating the transmitting antenna and the receiving antenna makes it possible to realize a highly sensitive sensor. Also, in bidirectional communication devices, by using different frequencies for the transmitting wave and the receiving wave, full-duplex communication that performs transmitting and receiving operations simultaneously can be realized without increasing the antenna size.

[0033] The radio wave lens of the present invention can also be applied to the antenna device described above. Figures 8A and 8B show an example of the radiation characteristics of the H-plane (XZ-plane) of an antenna device 10γ that radiates 60 GHz radio waves. Figure 8A shows the electric field distribution diagram, and Figure 8B shows the dependence of the antenna gain measured in the far field on the directionality angle. In Figure 8B, the horizontal axis shows the directionality angle (unit: deg), and the vertical axis shows the antenna gain (unit: dB). Also in Figure 8B, the solid line shows the case without radio wave lens 1γ, and the dashed line shows the case with radio wave lens 1γ attached. Measurement conditions such as frequency and measurement position are the same as those shown in Figures 2A and 2B.

[0034] As shown in Figures 2A and 2B, or Figures 3A and 3B, the horn antenna a1 described in Embodiment 1 has a horn portion with an axisymmetric shape in the XZ or YZ plane. Therefore, its radiation characteristics also exhibit an axisymmetric shape, and the directivity angle at which the antenna gain is maximized coincides with the front direction of the horn antenna a1 (θ=0deg). On the other hand, in the horn antenna a2 (solid line in Figure 8B), the two divided horn portions are used as transmitting and receiving antennas, respectively. Therefore, the shapes of the transmitting and receiving horn portions are not axisymmetric, and the directivity angle at which the antenna gain is maximized may deviate from the front direction of the horn antenna a2 (θ=0deg). For this reason, especially in the case of radio wave sensors, the receiving sensitivity of the two-part horn antenna a2 may be lower than the combined value of the maximum gains of the transmitting and receiving antennas.

[0035] In the electric field distribution diagram shown in Figure 8A, the propagation direction of the electric field wavefront radiated diagonally to the upper right from the transmitting section of the horn antenna a2 (right half in the figure) is corrected by the side wall of the radio lens 1γ to face the front of the horn antenna a2 (the +Z direction in the figure). Furthermore, in Figure 8B, as described above, when there is no radio lens 1γ (solid line), the directivity angle at which maximum gain is obtained is shifted to the right of the front direction of the horn antenna a2 (θ=0deg). However, when the radio lens 1γ is coupled to the horn antenna a2 (dashed line), the symmetry of the directivity angle dependence of the antenna gain is improved, and it can be seen that the maximum gain is obtained almost directly in front of the horn antenna a2 (θ=0deg).

[0036] Thus, the radio wave lens 1γ and antenna device 10γ of the third modification of the first embodiment are compatible with a two-part conical horn antenna a2, improving the axial symmetry of the radiation characteristics during transmission and reception operations, improving the sensitivity and directivity as a radio wave lens, reducing transmission loss in the case of a bidirectional communication device, and simplifying the system design.

[0037] Figure 9A shows a perspective view of a radio wave lens 2, which is an example of a radio wave lens according to the second embodiment, and an antenna device 20 using the radio wave lens 2. Figure 9B shows a cross-sectional view of the XZ plane along the VV line in Figure 9A. In Figures 9A and 9B, radio waves propagate in the Z-axis direction within the radio wave lens 2 and the horn antenna a3, forming an H plane in the XZ plane and an E plane in the YZ plane.

[0038] The radio wave lens 2 is made of a dielectric material and, as shown in Figures 9A and 9B, is coupled to a pyramidal horn antenna a3 having a rectangular aperture shape to constitute the antenna device 20. The aperture surface ap3 of the horn antenna a3 has a rectangular shape with adjacent sides of lengths e1 and e2 and opposite sides of equal length. The radio wave lens 2 has a constant cross-sectional shape and size, a rectangular cross-sectional shape that is substantially the same as the shape of the aperture surface ap3 of the horn antenna a3, and a cylindrical structure with side walls that are perpendicular to the aperture surface ap3. The lengths W1 and W2 of adjacent sides that constitute the inner shape of the rectangular cross-section of the radio wave lens 2 are substantially the same as the lengths e1 and e2 of adjacent sides of the aperture surface ap3 of the horn antenna a3. The first end 21 and second end 22, which are both ends of the radio wave lens 2, are open, and the first end 21 is coupled to the aperture surface ap3 of the horn antenna a3.

[0039] The radio wave lens 2 has sidewalls with thicknesses T1 and T2 on adjacent sides of its rectangular cross-section, while the sidewalls on opposite sides of the rectangular cross-section have the same thickness. Both T1 and T2 are approximately the same as the wavelength λe in the dielectric material of the radio waves transmitted and received by the horn antenna a3. Preferably, T1 and T2 differ to the same extent as the difference in wavelength between the H-plane and E-plane of the radio waves propagating through the radio wave lens 2. Therefore, for radio waves with a frequency of 60 GHz, the antenna characteristics can be optimized by selecting different thicknesses for the sidewalls T1 of the radio wave lens 2 perpendicular to the H-plane (XZ-plane) and T2 of the sidewalls perpendicular to the E-plane (YZ-plane), based on the characteristics of the E-plane and H-plane, with the wavelength λe in the dielectric material as the center.

[0040] The length L of the radio lens 2 is greater than or equal to the wavelength λ0 of the radio waves transmitted and received by the horn antenna a3 in air, and can be selected as the optimal value based on the relationship between antenna gain, directivity, and side lobes within a range of approximately 6 times λ0 or less.

[0041] The radio wave lens 2 has a structure that can be easily attached to the pyramidal horn antenna a3. The radio wave lens 2 and antenna device 20, as shown in Figures 2A and 2B, and Figures 3A and 3B, can increase antenna gain and narrow directivity with a lightweight and simple structure without increasing the size of the horn antenna a3.

[0042] In the second embodiment, as with the first modification of the first embodiment, the second end 22 of the radio wave lens 2 can also be closed with a half-wave plate. This prevents foreign matter from entering the horn antenna a3 while suppressing the increase in insertion loss due to the radio wave lens 2, thereby improving environmental resistance.

[0043] Furthermore, in the second embodiment, similar to the second modification of the first embodiment, the radio wave lens 2 can be formed integrally with the housing that houses the horn antenna a3. This prevents foreign matter from entering or adhering to the inside of the horn antenna a3 or the surrounding circuitry, thereby further improving environmental resistance.

[0044] Furthermore, in the second embodiment, similar to the third modification of the first embodiment, the radio wave lens 2 can be coupled to a two-part pyramidal horn antenna a4 with a partition wall as4, as shown in Figures 10A and 10B, thereby constituting the antenna device 20α. Figure 10A shows a perspective view of the radio wave lens 2α and antenna device 20α, which are modifications of the radio wave lens and antenna device of the second embodiment. Figure 10B shows a cross-sectional view of the XZ plane along the VI-VI line in Figure 10A. Similar to Figures 8A and 8B, the radio wave lens 2α improves the axial symmetry of the radiation characteristics during transmission and reception of the two-part pyramidal horn antenna a4, thereby facilitating the installation of the horn antenna a4 and the design of the transmission system.

[0045] The embodiments of the radio wave lens and the antenna device comprising the radio wave lens and the horn antenna have been described above, but the present invention is not limited thereto. For example, the radio waves propagating through the radio wave lens were described using the H plane and the E plane perpendicular to it as specific examples, but the H plane and E plane may be swapped. Furthermore, as a preferred example where the effects of the present invention are significant, the case of radiating or receiving radio waves in the millimeter wave band of 60 GHz was described, but the frequency may be higher or lower. For example, the frequency of the radio waves may be in the microwave band. In addition, multiple embodiments and their modifications described above may be combined. For example, the radio wave lens of the second embodiment may be formed to simultaneously have a lid portion, as in the first modification of the first embodiment, and a housing integrated configuration, as in the second modification of the first embodiment.

[0046] (summary) (1) One embodiment of a radio wave lens according to one aspect of the present invention is a radio wave lens connected to the aperture of a horn antenna that radiates and / or receives radio waves of a predetermined frequency, and is made of a dielectric material, has a cylindrical structure with a constant cross-sectional shape and size, and a length equal to or greater than the free-space wavelength of the radio wave, wherein the inner shape of the cross-section is substantially the same as the aperture of the horn antenna, and the thickness of the side wall of the cylindrical structure is substantially the same as the wavelength of the radio wave in the dielectric material.

[0047] According to the radio lens described in (1) above, it is possible to increase the gain of the horn antenna and narrow the radiation directivity with a lightweight and simple structure.

[0048] (2) According to another embodiment, in the radio wave lens of (1) above, the length is 1 to 6 times the free-space wavelength of the radio wave.

[0049] According to the radio wave lens described in (2) above, by precisely forming a lightweight and simple structure, it becomes possible to more accurately narrow the radiation directivity of the horn antenna.

[0050] (3) In another embodiment, the radio wave lens described in (1) to (2) above is configured to have a circular cross-sectional shape.

[0051] According to the radio wave lens described in (3) above, by making it a shape suitable for a conical horn antenna, it becomes possible to narrow the radiation directivity of the conical horn antenna.

[0052] (4) In yet another embodiment, the radio wave lens described in (1) to (2) above has a rectangular cross-sectional shape.

[0053] According to the radio wave lens described in (4) above, by making it a shape suitable for a pyramidal horn antenna, it becomes possible to narrow the radiation directivity of the pyramidal horn antenna.

[0054] (5) In yet another embodiment, in the radio wave lens of (4) above, the thickness of the side walls forming opposite sides of the cross section is the same, and the thickness of the side walls forming adjacent sides of the cross section is different.

[0055] According to the radio lens described in (5) above, by forming it into a shape more suitable for the electromagnetic field distribution of the pyramidal horn antenna, it becomes possible to more reliably narrow the radiation directivity of the pyramidal horn antenna.

[0056] (6) In yet another embodiment, in the radio wave lens of (1) to (5) above, the other end of the cylindrical structure that faces the end connected to the opening surface is closed by a lid that has the same or substantially the same dielectric constant as the dielectric material and has a thickness of substantially half the thickness of the side wall of the cylindrical structure.

[0057] According to the radio wave lens described in (6) above, by sealing the aperture surface, it is possible to minimize the insertion loss of the radio wave lens while improving the environmental resistance of the radio wave lens and the horn antenna connected to the radio wave lens.

[0058] (7) In yet another embodiment, the radio wave lens described in (1) to (6) above is configured to be integrally formed with the housing that covers the entire horn antenna.

[0059] According to the radio wave lens described in (7) above, by enclosing the entire horn antenna, it is possible to improve the environmental resistance of the radio wave lens and the horn antenna connected to the radio wave lens.

[0060] (8) In yet another embodiment, in the radio wave lens described in (1) to (7) above, the predetermined frequency is configured to be in the millimeter wave band.

[0061] According to the radio lens described in (8) above, by creating a structure optimized for the millimeter wave band, it becomes possible to reliably narrow the radiation directivity of the horn antenna in the millimeter wave band.

[0062] (9) According to one embodiment of an antenna device which is another aspect of the present invention, the device comprises the radio wave lens described in (1) to (8) above and the horn antenna.

[0063] According to the antenna device described in (9) above, by attaching a radio lens to the horn antenna, it is possible to narrow the radiation directivity with a lightweight and simple configuration.

[0064] (10) In another embodiment, in the antenna device of (9) above, the horn antenna is provided with a metal partition that divides the horn portion from the opening surface to the feed end into two parts along the direction of propagation of the radio waves.

[0065] According to the antenna device described in (10) above, by attaching a radio wave lens to a two-part horn antenna, the symmetry of the radiation directivity is improved, making it possible to simplify the installation of the antenna device and the design of the transmission system including the antenna device. [Explanation of Symbols]

[0066] 1, 1α, 1β, 1γ, 2, 2α radio lens 10, 10α, 10β, 10γ, 20, 20α Antenna Device 11, 21 First end 12, 22 Second end 13 Lid a1, a2, a3, a4 Horn antenna ap1, ap2, ap3 opening surface as2, as4 bulkhead CS cabinet

Claims

1. A radio wave lens connected to the aperture surface of a horn antenna that radiates and / or receives radio waves of a predetermined frequency, Formed from dielectric material, It has a cylindrical structure with a constant cross-sectional shape and size, and a length equal to or greater than the free-space wavelength of the radio wave. The internal shape of the cross-section is substantially the same in shape and size as the opening surface of the horn antenna. A radio wave lens in which the thickness of the side wall of the cylindrical structure is approximately the same as the wavelength of the radio waves in the dielectric material.

2. The radio wave lens according to claim 1, wherein the length is one to six times the free-space wavelength of the radio wave.

3. The radio wave lens according to claim 1, wherein the shape of the cross-section is circular.

4. The radio wave lens according to claim 1, wherein the cross-sectional shape is rectangular.

5. The radio wave lens according to claim 4, wherein the thickness of the side walls forming opposite sides of the cross-section is the same, and the thickness of the side walls forming adjacent sides of the cross-section is different.

6. The radio wave lens according to claim 1, wherein one end of the cylindrical structure that is connected to the opening surface is closed by a lid having the same or substantially the same dielectric constant as the dielectric material and having a thickness of substantially half the thickness of the side wall of the cylindrical structure.

7. The radio wave lens according to claim 6, which is integrally formed with a housing that covers the entire horn antenna.

8. The radio wave lens according to claim 1, wherein the predetermined frequency is in the millimeter wave band.

9. An antenna device comprising a radio wave lens according to any one of claims 1 to 8 and the horn antenna.

10. The antenna device according to claim 9, wherein the horn antenna is provided with a metal partition that divides the horn portion from the opening surface to the feed end into two parts along the direction of propagation of the radio waves.

Images