Dielectric lens and antenna module

Abstract

The present disclosure provides a dielectric lens capable of modifying a characteristic of an electromagnetic wave that is a plane wave, while allowing the electromagnetic wave to remain being a plane wave. A dielectric lens (1) has an input surface (2) and an output surface (3) opposite the input surface (2). The input surface (2) and the output surface (3) are each a curved surface and are rotationally symmetric about a virtual line (S). The shapes of the input surface (2) and the output surface (3) are not identical. When an electromagnetic wave that is a plane wave is caused to advance in a direction along the virtual line (S) to enter the input surface (2), the electromagnetic wave that is a plane wave is output from the output surface (3).

Description

[Technical Field]

[0001] The present disclosure relates to a dielectric lens and an antenna module, and more particularly to a dielectric lens that converts incident electromagnetic waves and emits them, and an antenna module including this dielectric lens. [Background technology]

[0002] Patent Document 1 discloses an array antenna in which a plurality of microstrip elements (element antennas) fabricated by etching are arranged on a resin substrate.

[0003] Furthermore, Patent Document 2 discloses that the electromagnetic waves radiated by the primary radiator are transmitted through a dielectric lens, thereby obtaining the required radiation directivity using only the dielectric lens. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-220418 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-246832 Summary of the Invention

[0005] An object of the present disclosure is to provide a dielectric lens that can change the characteristics of an electromagnetic wave that is a plane wave while maintaining the plane wave, and an antenna module that includes this dielectric lens.

[0006] A dielectric lens according to one aspect of the present disclosure has an incident surface and an exit surface opposite the incident surface, each of the incident surface and the exit surface being curved and rotationally symmetric about an imaginary line that intersects with both the incident surface and the exit surface, the incident surface and the exit surface not being identical in shape, and when an electromagnetic wave that is a plane wave is made to travel in a direction along the imaginary line and is incident on the incident surface, the electromagnetic wave that is a plane wave is emitted from the exit surface.

[0007] An antenna module according to one aspect of the present disclosure includes the dielectric lens and a radiator that emits an electromagnetic wave that is a plane wave, and causes the electromagnetic wave to travel in a direction along the imaginary straight line and enter the incident surface. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view of a dielectric lens and an antenna module according to an embodiment of the present disclosure. [Figure 2] FIG. 2 shows an example of an optical model for deriving the shapes of the entrance surface and the exit surface in this embodiment. [Figure 3] FIG. 3 is a graph showing the specific electromagnetic field intensity distribution of an incident wave set for specifically calculating the shape of a dielectric lens in an example of this embodiment. [Figure 4] FIG. 4 is a graph showing the specific electromagnetic field intensity distribution of the emitted wave set for specifically calculating the shape of the dielectric lens in an example of this embodiment. [Figure 5] FIG. 5 is a diagram showing the shape of the dielectric lens identified in the example of this embodiment. [Figure 6] FIG. 6 is a diagram showing the results of an electromagnetic field simulation when an electromagnetic wave passes through a dielectric lens in an example of this embodiment. [Figure 7] FIG. 7 is a graph showing the specific electromagnetic field intensity distribution of the output wave extracted from the electromagnetic field simulation results of FIG. [Figure 8]FIG. 8 is a graph showing the specific electromagnetic field intensity distribution of the incident wave extracted from the electromagnetic field simulation results of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] With the shift to higher frequency bands in wireless communication systems, the evolution of communication methods, and the practical application of sensor systems using electromagnetic waves, the antenna characteristics required for the electromagnetic waves emitted from antenna modules, such as directivity, are becoming increasingly diverse. In order for electromagnetic waves to have high directivity, they must be plane waves. Furthermore, the directivity of electromagnetic waves is affected by the beam diameter and electromagnetic field intensity distribution of the electromagnetic waves.

[0010] Therefore, in order to change the directivity of the electromagnetic waves emitted by the antenna module, the antenna module must be redesigned from scratch, which requires a great deal of effort and cost. For example, in the case of an array antenna such as that disclosed in Patent Document 1 (JP 2012-220418 A), the shape, number, arrangement, power supply output, etc. of the element antennas must be redesigned so that the electromagnetic waves have a desired beam diameter and electromagnetic field intensity distribution.

[0011] In order to solve the above problems, the inventors have considered that it would be sufficient to have a dielectric lens that converts a plane wave having a certain beam diameter and electromagnetic field intensity distribution into a desired beam diameter and electromagnetic field intensity distribution.

[0012] For example, the technology described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-246832) uses a dielectric lens to convert the electromagnetic waves radiated from a primary radiator and give them directivity, but it does not change the directivity of an antenna device that emits a plane wave.

[0013] Therefore, the inventors have conducted research to develop a dielectric lens that can change the characteristics of a plane wave electromagnetic wave while maintaining the plane wave, and have completed the present disclosure. Note that the details of this development do not limit the content of the present disclosure.

[0014] A dielectric lens 1 and an antenna module 10 according to this embodiment will be described with reference to Fig. 1. The dashed lines in Fig. 1 represent the direction in which electromagnetic waves travel and the electromagnetic field intensity distribution of the electromagnetic waves.

[0015] The dielectric lens 1 has an incident surface 2 and an exit surface 3 opposite the incident surface 2. The incident surface 2 and the exit surface 3 are each curved and rotationally symmetric about an imaginary line S that intersects with both the incident surface 2 and the exit surface 3. The incident surface 2 and the exit surface 3 do not have the same shape. When an electromagnetic wave (hereinafter also referred to as an incident wave I) that is a plane wave travels in a direction along the imaginary line S and is incident on the incident surface 2, an electromagnetic wave (hereinafter also referred to as an exit wave E) that is a plane wave is emitted from the exit surface 3. In other words, although the shapes of the incident surface 2 and the exit surface 3 are not identical, the incident surface 2 and the exit surface 3 are each shaped so that when an incident wave I travels in a direction along the imaginary line S and is incident on the incident surface 2, an exit wave E that is a plane wave is emitted from the exit surface 3.

[0016] In this embodiment, whether an electromagnetic wave is a plane wave can be confirmed by the following method. An oscillation component of frequency f of the electromagnetic wave is extracted from the fluctuating electromagnetic field components at a certain point in space through which the electromagnetic wave of frequency f passes, and its oscillation phase is measured. A plane consisting of a set of points with the same oscillation phase extracted in this way is called a phase plane. When a phase plane defined in this way is contained between two imaginary planes that are orthogonal to the imaginary line S and spaced apart by an interval of (1 / 4) × λ, the electromagnetic wave is considered to be a plane wave. λ is the wavelength of the electromagnetic wave in a vacuum, and is defined by the equation λ = c / f, where f is the frequency of the electromagnetic wave and c is the speed of light in a vacuum.

[0017] In this embodiment, the focal length of the plane wave is at infinity or can be regarded as the same as infinity.

[0018] According to this embodiment, the dielectric lens 1 can be used to convert the incident wave I, which is a plane wave, into the output wave E, which is also a plane wave. Furthermore, since the incident surface 2 and the output surface 3 do not have the same shape, the electromagnetic field distribution of the incident wave I and the electromagnetic field distribution of the output wave E can be made different, and the beam radius of the incident wave I and the beam radius of the output wave E can also be made different. Therefore, the dielectric lens 1 alone can convert the incident wave I, which is a plane wave, into the output wave E, which is a plane wave with different characteristics from the incident wave I. In other words, the dielectric lens 1 can change the characteristics of the electromagnetic wave, which is a plane wave, while maintaining its plane wave nature.

[0019] The dielectric lens 1 is preferably made of an isotropic dielectric. An isotropic dielectric is a material in which only the diagonal components of the dielectric tensor have values, and these components have the same value. Specific examples of isotropic dielectrics include glass with no internal stress, low-dielectric-constant resins such as fluororesin with no internal stress, water, and air. The dielectric lens 1 is made of, for example, glass or low-dielectric-constant resins. The dielectric constant of the dielectric lens 1 is, for example, 1.8 or more and 6.5 or less. The dielectric constant of the dielectric lens 1 is appropriately designed depending on the application, etc., and does not necessarily have to be within the above range.

[0020] As described above, the dielectric lens 1 has an incident surface 2 and an exit surface 3. The incident surface 2 and the exit surface 3 are aligned along a virtual line S that intersects both the incident surface 2 and the exit surface 3. The incident surface 2 faces the opposite side of the exit surface 3 from the incident surface 2, and the exit surface 3 faces the opposite side of the incident surface 2 from the exit surface 3. The incident surface 2 and the exit surface 3 are both rotationally symmetrical about the virtual line S. Therefore, the virtual line S can be said to be a line that intersects the incident surface 2 at the center of the incident surface 2 and intersects the exit surface 3 at the center of the exit surface 3. Furthermore, the shapes of the incident surface 2 and the exit surface 3 are different. This allows the electromagnetic field distribution of the incident wave I to differ from the electromagnetic field distribution of the exit wave E, or further allows the beam radii of the incident wave I and the exit wave E to differ from each other.

[0021] As described above, it is preferable that the incident wave I and the outgoing wave E have different electromagnetic field intensity distributions. This allows the characteristics of the outgoing wave E to be different from those of the incident wave I.

[0022] When making the electromagnetic field intensity distributions different between the incident wave I and the outgoing wave E, if the electromagnetic field intensity distribution of the incident wave I is uniform in the direction perpendicular to the imaginary line S, it is preferable that the electromagnetic field intensity distribution of the outgoing wave E becomes sparser the further it is from the imaginary line S. Electromagnetic waves emitted from the outer edge of the emission surface 3 tend to become spherical waves, and these spherical waves tend to cause the generation of unwanted electromagnetic waves such as side lobes due to interference. However, if the electromagnetic field intensity distribution of the outgoing wave E becomes sparser the further it is from the imaginary line S, the electromagnetic field intensity distribution of the electromagnetic waves emitted from the outer edge of the emission surface 3 becomes lower, and therefore side lobes are less likely to occur.

[0023] As described above, it is preferable that the beam radius of the incident wave I and the beam radius of the output wave E are different from each other. This allows the directivity of the output wave E to be different from that of the incident wave I. In other words, if the beam radius of the output wave E is larger than the beam radius of the incident wave I, the directivity of the output wave E can be made higher than that of the incident wave I, and if the beam radius of the output wave E is smaller than the beam radius of the incident wave I, the directivity of the output wave E can be made lower than that of the incident wave I.

[0024] An example of a specific shape of the entrance surface 2 and the exit surface 3 for realizing the above-mentioned dielectric lens 1 will be described.

[0025] The refractive index of the dielectric lens 1 is n. The axis passing through the virtual line S is defined as the z-axis, and an arbitrary axis perpendicular to the z-axis is defined as the x-axis. The z-axis coordinate value of the intersection of the z-axis and the incident surface 2 is defined as z c1 , and the z-axis coordinate value of the intersection of the z-axis and the exit surface 3 is z c2 Let's say.

[0026] In this coordinate plane, it is preferable that the coordinate (z1(r), r) on the incident surface 2 where the x-axis coordinate value is r and the coordinate (z2(R), R) on the exit surface 3 where the x-coordinate value is R satisfy the following formula: The coordinates (z1(r), r) and the coordinates (z2(R), R) have a relationship in which the part of the incident wave I that is incident at the coordinate (z1(r), r) is emitted from the coordinate (z2(R), R) as part of the exit wave E, and R is represented by R(r), which is a function of r.

[0027]

number

[0028] As shown in the optical model in FIG. 2, z c1 is the z-axis coordinate value of the intersection point between the z-axis and the incident surface 2, z c2 is the z-axis coordinate value of the intersection of the z-axis and the emission surface 3. P1(r) is a function that indicates the electromagnetic field intensity distribution of the incident wave I at the position on the coordinate plane where the x-axis coordinate value is r, and P2(R) is a function that indicates the electromagnetic field intensity distribution of the emission wave E at the position on the coordinate plane where the x-axis coordinate value is R. However, 0≦r≦r max , and 0≦R≦R max That is, r max is the radius of the entrance surface 2, and R max is the radius of the exit surface 3. Note that r max and R max and φ(r) are preferably equal to or greater than twice the wavelength of the incident wave I in a vacuum. φ(r) is an auxiliary variable, and is a function that indicates the refraction angle when the incident wave I enters the dielectric lens 1 from the incident surface 2 at a position on the coordinate plane where the x-axis coordinate value is r, and φ(0) is 0. Note that the optical model in FIG. 2 does not accurately represent the shape of the dielectric lens 1.

[0029] The four equations shown in the above [Mathematical Expression 1] were independently derived by the inventors by using the above-mentioned coordinate system and the quantities expressed on that coordinate system to express the law of refraction (Snell's law) at the entrance surface 2 and the exit surface 3, the law of conservation of energy for electromagnetic waves, and the law of constant optical path length within the category of geometric optics. If the shape z1(r) of the entrance surface 2 and the shape z2(R) of the exit surface 3 are taken as undetermined functions, the law of refraction can be expressed as a first-order differential equation of z1(r) and z2(R). Therefore, if the quantities other than z1(r) and z2(R) are given as initial conditions, the undetermined functions z1(r) and z2(R) can be determined from four independent equations.

[0030] Furthermore, the inventors have confirmed the validity of the above formula through numerical verification experiments shown in the Examples section.

[0031] The shapes of the incident surface 2 and the exit surface 3 defined by the above [Equation 1] are allowed for dimensional errors that may normally occur. For example, when the relative dielectric constant is ε r When the dielectric lens 1 is used to convert an incident wave I of wavelength λ in a vacuum, the shape of the incident surface 2 and the shape of the exit surface 3 each have a -λ / 16 / ε r 1 / 2 More than λ / 16 / ε r 1 / 2 At least the following dimensional errors are allowed. Specifically, when the material of the dielectric lens 1 is a fluororesin (polytetrafluoroethylene) with a relative dielectric constant of 2.0, and the dielectric lens 1 is used to convert an incident wave I having a frequency of 79 GHz (i.e., a wavelength of 3.8 mm in a vacuum), which is used for automobile collision prevention radar, the shapes of the entrance surface 2 and the exit surface 3 each have a tolerance of -3.8 / 16 / 2.0 in the direction along the imaginary line S. 1 / 2 mm or more 3.8 / 16 / 2.0 1 / 2 A dimensional error of less than mm, i.e., between -0.17 mm and 0.17 mm, is permitted.

[0032] In general, it is preferable that the value of the electromagnetic field intensity distribution of the output wave E, which is expressed as a function of P2(R), be specified so that it decreases as the value of R increases. For example, it is preferable that the electromagnetic field intensity distribution, which is expressed as a function of P2(R), have a Gaussian distribution. In this case, the electromagnetic field intensity distribution of the output wave E becomes sparser the further it is from the imaginary line S, making it less likely that side lobes will occur. Note that P1(r) and P2(R) can be freely set by the designer. Specifically, for example, by using an electromagnetic field intensity distribution, such as a Chebyshev distribution, that has the sharpest directivity while having a specified side lobe value, it is possible to increase the directivity (gain) while suppressing the side lobes.

[0033] The above r max and R max The value of is, for example, r max <R max In this case, the beam radius of the outgoing wave E is larger than the beam radius of the incident wave I, and therefore the dielectric lens 1 can increase the directivity of the outgoing wave E, i.e., increase the gain. max and R max The value of r max >R max In this case, the beam radius of the outgoing wave E is smaller than the beam radius of the incident wave I, and therefore the dielectric lens 1 can reduce the directivity of the outgoing wave E.

[0034] The antenna module 10 according to this embodiment will be described.

[0035] The antenna module 10 includes a dielectric lens 1 and a radiator 4. The radiator 4 emits an electromagnetic wave, which is a plane wave, and causes this electromagnetic wave to travel in a direction along an imaginary straight line S and be incident on the incident surface 2 of the dielectric lens 1. The electromagnetic wave emitted by the radiator 4 becomes the incident wave I described above.

[0036] The radiator 4 includes an antenna 5 that emits electromagnetic waves that are plane waves. The antenna 5 is, for example, an array antenna that includes a plurality of antenna elements. However, the configuration of the antenna 5 is not limited to only an array antenna.

[0037] The dielectric lens 1 is positioned, for example, so that the antenna 5 of the radiator 4 and the incident surface 2 of the dielectric lens 1 face each other, and so that the central axis (optical axis) of the electromagnetic wave (incident wave I) emitted by the radiator 4 overlaps with the above-mentioned virtual straight line S.

[0038] The incident surface 2 and the exit surface 3 of the dielectric lens 1 have shapes defined by the above equation, for example. In this case, the electromagnetic field intensity distribution at the position where the x-axis coordinate value of the electromagnetic wave (incident wave I) emitted by the radiator 4 is r is represented by the above function P1(r), and the beam radius of the incident wave I is r. max In this case, the electromagnetic field intensity distribution at the position where the x-axis coordinate value of the output wave E emitted from the dielectric lens 1 is R is expressed by the above-mentioned function P1(R), and the beam radius of the output wave E is R. max In this way, the dielectric lens 1 can change the characteristics of the electromagnetic wave, which is a plane wave emitted by the radiator 4, while maintaining the plane wave.

[0039] Therefore, according to this embodiment, even when using the same radiator 4, it is possible to realize an antenna module 10 that emits a plane wave with desired characteristics simply by changing the shape of the dielectric lens 1. That is, in this embodiment, in the antenna module 10 including the radiator 4 that emits a plane wave, in order to achieve the desired characteristics of the plane wave emitted by this antenna module 10, it is only necessary to design the shape of the dielectric lens 1 without having to design the antenna 5 of the radiator 4 individually.

[0040] In this embodiment, the dielectric lens 1 can also serve as a radome. In this case, the radome, which is originally part of the casing, can be given the function of changing the characteristics of the electromagnetic wave, which is a plane wave. Furthermore, by changing the shape of the radome, it is possible to realize an antenna module 10 that emits a plane wave with desired characteristics. [Example]

[0041] Below are shown specific design results of the dielectric lens calculated using the formula shown in [Mathematical Expression 1] of this embodiment, and the results of numerical experiments using an electromagnetic field simulator (finite element method) to confirm whether the designed dielectric lens operates correctly. Note that this embodiment is not limited by the following content.

[0042] First, in order to specifically calculate the shape of the dielectric lens using the formula shown in [Mathematical Expression 1], the following initial conditions were set. -Dielectric constant (ε r ):1.96 - Shape of entrance surface: circular -Aperture diameter of the entrance surface (2×r max ):2 - Shape of the exit surface: circular -Aperture diameter of the exit surface (2×R max ):3.8 -Distance between the intersection of the virtual line and the incident surface and the intersection of the virtual line and the exit surface: 2.0 - Electromagnetic field strength distribution of incident wave: uniform distribution as shown in Figure 3. The distribution shown in Figure 3 is the distribution of specific electromagnetic field strength, which is the value obtained by dividing the electromagnetic field strength on the incident plane by the electromagnetic field strength at the intersection of the imaginary line and the incident plane. Although specific electromagnetic field strength is a dimensionless quantity, the specific electromagnetic field strength shown in Figure 3 is shown in dB, and therefore the specific electromagnetic field strength on the imaginary line is 0 dB. - Electromagnetic field intensity distribution of output wave: -30 dB n=4 pseudo Taylor distribution shown in Figure 4. Note that Figure 4 shows the distribution of the specific electromagnetic field intensity, which is the value obtained by dividing the electromagnetic field intensity on the output surface 3 by the electromagnetic field intensity at the intersection of a virtual line and the output surface 3. The specific electromagnetic field intensity shown in Figure 4 is shown in dB.

[0043] The design guidelines and precautions used when selecting the above initial conditions are explained below.

[0044] Polytetrafluoroethylene was selected as the dielectric material for the dielectric lens. Therefore, the relative permittivity ε rwas set to 1.96. Note that attenuation of electromagnetic waves due to dielectric loss is often a problem in high frequency bands above the millimeter wave band, and polytetrafluoroethylene has low dielectric loss, so it is often used as a dielectric lens material in frequency bands above the millimeter wave band.

[0045] In addition, in this design, by combining an antenna that has a circular aperture and emits electromagnetic waves with a uniform electromagnetic field intensity distribution with the dielectric lens of this embodiment, we aimed to reduce the side lobes of the electromagnetic waves (suppression of unnecessary radiated electromagnetic waves) and increase the gain (narrow beam).

[0046] The relative permittivity intensity distribution on the emission surface was set based on the above-described conditions. While a circular aperture antenna with a uniform relative electromagnetic field intensity distribution is easy to design and manufacture, it inevitably generates side lobes (unwanted electromagnetic waves other than the main beam) with a relative electromagnetic field intensity higher than −17.6 dB relative to the maximum electromagnetic field intensity of the main beam (electromagnetic waves emitted in the optical axis direction). Therefore, antennas emitting electromagnetic waves with a uniform relative electromagnetic field intensity cannot be used in communication systems that require unwanted radiation suppression with a side lobe relative electromagnetic field intensity of −17.6 dB or less (for example, automobile collision prevention radar requires unwanted radiation suppression with a side lobe relative electromagnetic field intensity of −20 dB or less). Therefore, it is necessary to design and use an antenna with better unwanted radiation suppression, or to correct the electromagnetic waves by combining the antenna with the dielectric lens of this embodiment.

[0047] Based on the above design guidelines, in this embodiment, a specific electromagnetic field intensity distribution (-30 dB n=4 pseudo Taylor distribution) on the emission surface was set so that the specific electromagnetic field intensity of the side lobe of the emission wave was -30 dB or less.

[0048] In the above initial conditions, the aperture diameters of the entrance and exit surfaces and the distance between the entrance and exit surfaces are dimensionless, but because the design method using [Equation 1] is a method in the domain of geometrical optics, which is frequency-independent, only the ratio of these three dimensions is important, and there is no need to set the actual size as an initial condition in the design stage using [Equation 1]. Therefore, to make it easier to understand the ratio of each dimension to the aperture diameter of the entrance surface, the aperture radius of the exit surface is set to 1 as an initial condition. Note that the above three dimensions can be scaled and converted to actual sizes only after the various frequency-dependent antenna specifications, such as antenna gain, actually required in a communication system, are specified.

[0049] Figure 5 shows the shape of the dielectric lens identified by applying the above initial conditions to [Equation 1] and numerically solving the simultaneous differential equations that make up [Equation 1] using the Runge-Kutta method. Figure 5 shows that the shapes of the entrance and exit surfaces are both aspherical. Figure 5 also shows the path of the electromagnetic wave determined by ray tracing based on the shapes of the entrance and exit surfaces. The electromagnetic wave is incident on the dielectric lens so that its optical axis passes through the center of the entrance and exit surfaces, i.e., so that the optical axis of the electromagnetic wave overlaps with the virtual line S mentioned above. The path of the electromagnetic wave is represented by multiple lines indicating the direction of propagation of the electromagnetic wave, and the density of these lines represents the intensity of the electromagnetic wave. The incident wave set under the above initial conditions is a plane wave with uniform electromagnetic field intensity across the entire aperture surface that propagates in a direction parallel to the optical axis. Therefore, the path of the incident wave in Figure 5 is represented by equally spaced straight lines parallel to the optical axis. When an electromagnetic wave passes through the incident surface, it is refracted so that it moves further away from the optical axis the further away it is from the optical axis, which causes the beam diameter of the electromagnetic wave to expand within the dielectric lens 1. The electromagnetic wave emitted from the exit surface (emitted wave) is represented by parallel lines parallel to the optical axis, and the spacing between these parallel lines increases the further away it is from the optical axis. This indicates that the emitted wave is a plane wave that travels in a direction parallel to the optical axis, and that the relative electromagnetic field intensity of the emitted wave attenuates the further away it is from the optical axis.

[0050] To confirm the validity of the dielectric lens design method using the above [Equation 1], we performed an electromagnetic field simulation to confirm that a plane wave with a uniform specific electromagnetic field intensity distribution is converted into a plane wave with a specific electromagnetic field intensity distribution of -30 dB n=4 pseudo Taylor distribution when it passes through a dielectric lens designed as shown in Figure 5. The results are shown below.

[0051] Since actual dimensions are required to perform electromagnetic field simulations, the dimensions of the dielectric lens were set as follows by enlarging the shape of the dielectric lens shown in Figure 5 to the same scale. - Calculation frequency (frequency of electromagnetic waves): 79 GHz (wavelength 3.80 mm) - Diameter of incident surface: 19mm (5 times the wavelength of the electromagnetic wave) - Diameter of the exit surface: 36.1 mm (9.5 times the wavelength of the electromagnetic wave) -Distance between the incident and exit surfaces: 38 mm (10 times the wavelength of the electromagnetic wave) -Electromagnetic field simulator used: Femtet 2020.1.2 64bit

[0052] Furthermore, once the diameter of the incident surface is specified, the dimensions of the dielectric lens other than the diameter of the incident surface are uniquely determined from the initial conditions set in the design using [Equation 1]. The diameter of the incident surface was selected as above, taking into consideration the calculation time required for electromagnetic field simulation and the aperture diameter of the dielectric lens, which establishes geometric optics, the basis of [Equation 1]. The larger the aperture diameter of the dielectric lens compared to the wavelength of the electromagnetic wave, the closer the geometric optics matches the behavior of the actual electromagnetic wave. However, with a dielectric lens with such a large aperture diameter, the analysis area becomes larger, and electromagnetic field simulation requires an enormous amount of time. The diameter of the incident surface was set based on these two conflicting considerations.

[0053] Figure 6 shows the results of an electromagnetic field simulation when an electromagnetic wave passes through a dielectric lens under the above conditions. Figure 6 shows how a plane wave with a uniform electric field intensity distribution and parallel electric field vectors is refracted at the entrance and exit surfaces when it enters a dielectric lens so that its optical axis passes through the center of the entrance and exit surfaces, i.e., so that the optical axis overlaps with the virtual line S mentioned above. The optical axis coincides with the bottom edge of Figure 6. The shading in Figure 6 indicates the strength of the electromagnetic field, with whiter areas representing stronger electromagnetic field strength. Figure 6 shows that when an electromagnetic wave enters the entrance surface from the left side, the electromagnetic wave traveling through the dielectric lens is almost a plane wave near the optical axis, but diverges away from the optical axis as it moves away from the optical axis. Next, when the electromagnetic wave passes through the exit surface, it becomes a plane wave again, but the electromagnetic field strength weakens the further it moves from the optical axis. Furthermore, based on the spacing of the stripes formed by the shading in Figure 6, it is observed that the wavelength of the electromagnetic wave is shortened (0.71 times) inversely proportional to the 1 / 2 power of the relative dielectric constant (1.96) inside the dielectric lens. From the above, it can be qualitatively confirmed that the dielectric lens design method based on [Equation 1] of this embodiment functions correctly.

[0054] Furthermore, in order to quantitatively confirm the electromagnetic field intensity distribution shown in Figure 6, we investigated whether the electric field intensity distribution of the output wave calculated by electromagnetic field simulation matches the -30 dB n=4 pseudo Taylor distribution assumed at the time of design. The results are shown below.

[0055] Figures 7 and 8 show the specific electromagnetic field strength distributions extracted from the electromagnetic field simulation results of Figure 6. Figure 7 shows the specific electromagnetic field strength distribution of the outgoing wave on the axis along the right side of Figure 6, and Figure 8 shows the specific electromagnetic field strength distribution of the incident wave on the axis along the left side of Figure 6.

[0056] In FIG. 7, the horizontal axis represents the distance from the optical axis when the radius of the exit surface is set to 1. The circles in FIG. 7 represent the relative electromagnetic field intensity calculated by electromagnetic field simulation. The solid line in FIG. 7 represents the relative electromagnetic field intensity distribution after the -30 dB n=4 pseudo Taylor distribution is corrected by modified surface methodology, taking into account the return loss at each of the entrance and exit surfaces. Note that the modified surface methodology refers to the dielectric lens design method in this embodiment using [Equation 1]. In this example, the shapes of the entrance and exit surfaces were designed without taking into account the return loss at each of the entrance and exit surfaces. However, for quantitative confirmation, the result of correcting the initial -30 dB n=4 pseudo Taylor distribution taking into account the return loss should be compared with the relative electromagnetic field intensity calculated by electromagnetic field simulation.

[0057] In Fig. 8, the horizontal axis represents the distance from the optical axis when the radius of the incident surface is set to 1. The circles in Fig. 8 represent the specific electromagnetic field strength calculated by electromagnetic field simulation. The solid line in Fig. 8 represents the uniform specific electromagnetic field strength distribution set as the initial condition.

[0058] Figure 7 shows a difference of less than 3 dB near the optical axis and about 5 dB around the exit surface between the results of the electromagnetic field simulation and the transmittance of the dielectric lens obtained by the modified surface method. However, Figure 8 shows that the difference in the relative electromagnetic field strength of the electromagnetic wave on the incident surface side is at most 3 dB or more, so the difference between the results of the electromagnetic field simulation shown in Figure 7 and the transmittance of the dielectric lens obtained by the modified surface method is within a reasonable range, and it can be determined that the two are consistent. Note that the non-uniformity in the relative electromagnetic field strength calculated by the electromagnetic field simulation shown in Figure 8 occurs due to the small analysis region (the diameter of the incident surface) and is not caused by the electromagnetic field simulator used.

[0059] As is clear from the above embodiment, the dielectric lens (1) according to the first aspect of the present disclosure has an incident surface (2) and an exit surface (3) opposite to the incident surface (2). Each of the incident surface (2) and the exit surface (3) is a curved surface and is rotationally symmetric about an imaginary line (S) that intersects with both the incident surface (2) and the exit surface (3). The incident surface (2) and the exit surface (3) do not have the same shape. When an electromagnetic wave that is a plane wave travels in a direction along the imaginary line (S) and is incident on the incident surface (2), the electromagnetic wave that is a plane wave is emitted from the exit surface (3).

[0060] According to the first aspect, the dielectric lens (1) can change the characteristics of an electromagnetic wave that is a plane wave while maintaining the plane wave.

[0061] In the second aspect of the present disclosure, the electromagnetic wave incident on the incident surface (2) and the electromagnetic wave emitted from the emission surface (3) in the first aspect have electromagnetic field intensity distributions that are different from each other.

[0062] According to the second aspect, the electromagnetic wave emitted from the emission surface (3) can be made different from the electromagnetic wave incident on the incidence surface (2).

[0063] In a third aspect of the present disclosure, in the first or second aspect, the beam radius of the electromagnetic wave incident on the incident surface (2) and the beam radius of the electromagnetic wave emitted from the exit surface (3) are different from each other.

[0064] According to the third aspect, the directivity of the electromagnetic waves emitted from the emission surface (3) can be made different from that of the electromagnetic waves incident on the incidence surface (2).

[0065] In a fourth aspect of the present disclosure, in any one of the first to third aspects, when the electromagnetic field intensity distribution of the electromagnetic waves incident on the incident surface (2) is uniform in a direction perpendicular to the imaginary straight line (S), the electromagnetic field intensity distribution of the electromagnetic waves exiting from the exit surface (3) becomes sparser the farther it is from the imaginary straight line (S).

[0066] According to the fourth aspect, the electromagnetic field intensity distribution of the electromagnetic waves emitted from the outer edge of the emission surface (3) is low, and therefore side lobes are less likely to occur.

[0067] In a fifth aspect of the present disclosure, in any one of the first to fourth aspects, when the refractive index of the dielectric lens (1) is n and a coordinate plane is defined in which an axis passing through the virtual line (S) is the z-axis and an arbitrary axis perpendicular to the z-axis is the x-axis, the coordinate (z1(r), r) on the incident surface (2) where the x-axis coordinate value is r and the coordinate (z2(R), R) on the exit surface (3) where the x-coordinate value is R satisfy the following formula, where R is represented by R(r), which is a function of r.

number

[0068] According to the fifth aspect, it is possible to realize a dielectric lens (1) that can change the characteristics of an electromagnetic wave that is a plane wave while maintaining the plane wave.

[0069] An antenna module (10) according to a sixth aspect of the present disclosure includes a dielectric lens (1) according to any one of the first to fifth aspects, and a radiator (4) that emits an electromagnetic wave that is a plane wave, and causes the wave to travel in a direction along an imaginary straight line (S) and enter an incident surface (2).

[0070] According to the sixth aspect, the dielectric lens (1) can change the characteristics of the electromagnetic wave, which is a plane wave emitted by the radiator (4), while maintaining the plane wave.

[0071] In a seventh aspect of the present disclosure, the dielectric lens (1) in the sixth aspect also serves as a radome.

[0072] In the seventh aspect, the radome, which is essentially a part of the casing, can be given the function of changing the characteristics of electromagnetic waves, which are plane waves. [Explanation of symbols]

[0073] 1. Dielectric Lens 2 Incidence plane 3. Exit surface 4 Radiators 5 Antennas

Claims

1. an entrance surface and an exit surface opposite the entrance surface; each of the incident surface and the exit surface is a curved surface and is rotationally symmetric about a virtual line that intersects with both the incident surface and the exit surface; The entrance surface and the exit surface do not have the same shape, a dielectric lens in which, when an electromagnetic wave that is a plane wave is made to travel in a direction along the imaginary straight line and is incident on the incident surface, the electromagnetic wave that is a plane wave is emitted from the exit surface; The refractive index of the dielectric lens is n, If a coordinate plane is defined in which the axis passing through the virtual line is the z-axis and an arbitrary axis perpendicular to the z-axis is the x-axis, then: In the coordinate plane, the coordinate (z 1 (r), r) on the incident surface where the x-axis coordinate value is r and the coordinate (z 2 (R), R) on the exit surface where the x-coordinate value is R satisfy the following formula, where R is represented by R(r) which is a function of r: [Equation 1] In the above formula, z c1 is the z-axis coordinate value of the intersection point between the z-axis and the incident surface, z c2 is the z-axis coordinate value of the intersection point between the z-axis and the exit surface, P 1 (r) is a function indicating the electromagnetic field intensity distribution of electromagnetic waves incident on the incident surface at a position on the coordinate plane whose x-axis coordinate value is r, and P 2 (R) is a function indicating the electromagnetic field intensity distribution of electromagnetic waves exiting from the exit surface at a position on the coordinate plane whose x-axis coordinate value is R, where 0≦r≦r max and 0≦R≦R max ; φ(r) is an auxiliary variable and is a function indicating the refraction angle when an electromagnetic wave is incident into the dielectric lens from the incident surface at a position where the x-axis coordinate value on the coordinate plane is r, and φ(0) is 0. Dielectric lens.

2. the electromagnetic wave incident on the incident surface and the electromagnetic wave emitted from the emission surface have electromagnetic field intensity distributions different from each other; The dielectric lens according to claim 1 .

3. a beam radius of the electromagnetic wave incident on the incident surface and a beam radius of the electromagnetic wave emitted from the emission surface are different from each other; 3. The dielectric lens according to claim 1 or 2.

4. When the electromagnetic field intensity distribution of the electromagnetic wave incident on the incident surface is uniform in a direction perpendicular to the imaginary line, the electromagnetic field intensity distribution of the electromagnetic wave exiting from the exit surface becomes sparser as it moves away from the imaginary line.

3. The dielectric lens according to claim 1 or 2.

5. When the electromagnetic field intensity distribution of the electromagnetic wave incident on the incident surface is uniform in a direction perpendicular to the imaginary line, the electromagnetic field intensity distribution of the electromagnetic wave exiting from the exit surface becomes sparser as it moves away from the imaginary line. The dielectric lens according to claim 3 .

6. A dielectric lens according to claim 1; a radiator that emits an electromagnetic wave that is a plane wave, and causes the electromagnetic wave to travel in a direction along the imaginary straight line and enter the incident surface, Antenna module.

7. The dielectric lens also serves as a radome. The antenna module according to claim 6 .

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