CN110336137B - Impedance matching high-gain lens antenna and design method thereof - Google Patents
Impedance matching high-gain lens antenna and design method thereof Download PDFInfo
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- CN110336137B CN110336137B CN201910675021.6A CN201910675021A CN110336137B CN 110336137 B CN110336137 B CN 110336137B CN 201910675021 A CN201910675021 A CN 201910675021A CN 110336137 B CN110336137 B CN 110336137B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/02—Waveguide horns
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/02—Waveguide horns
- H01Q13/0283—Apparatus or processes specially provided for manufacturing horns
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/02—Refracting or diffracting devices, e.g. lens, prism
- H01Q15/08—Refracting or diffracting devices, e.g. lens, prism formed of solid dielectric material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
- H01Q19/06—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens
- H01Q19/062—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens for focusing
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
- H01Q19/06—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens
- H01Q19/08—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens for modifying the radiation pattern of a radiating horn in which it is located
Abstract
The invention discloses an impedance matching high-gain lens antenna and a design method thereof, wherein the impedance matching lens antenna comprises an impedance matching lens and an H-face sector horn antenna loaded with a waveguide extension section, and the caliber of the H-face sector horn antenna is connected with the waveguide extension section with the same caliber size and used for fixing the impedance matching lens; the length of the waveguide extension segment is equal to the width of the impedance matching lens, and the waveguide extension segment is used for fixing the impedance matching lens and completely covering the side face of the impedance matching lens. An electromagnetic wave signal excited by a signal source radiates cylindrical waves through an H-plane sector horn antenna, then the cylindrical waves are corrected through an impedance matching lens phase and converted into two-dimensional plane waves with equal phase planes perpendicular to the propagation direction, and finally the two-dimensional plane waves radiate to a free space. The lens antenna has the advantages of wide working frequency band, small loss, high gain, good far field directionality, low level of the side lobe, small size and the like, can normally work in an X wave band, and has very high practical value in the aspects of electromagnetic imaging and communication.
Description
Technical Field
The invention relates to an impedance matching high-gain lens antenna, belonging to the field of novel artificial electromagnetic devices and a design method thereof.
Background
As a device for effectively receiving and radiating electromagnetic waves, directivity is an important measure of the performance of an antenna. The radiation wave of the traditional H-surface fan-shaped horn antenna is in a cylindrical surface wave form, a central radiation area and an edge area have large phase deviation, and the directionality is poor. The lens is used for correcting phase wavefront from the radiation source, reducing phase deviation of the center and the edge of the wavefront and improving directionality. Compared with the traditional antenna, the lens antenna has more controllable parameters, the medium, shape, focal diameter ratio and the like of the lens are adjustable, the design is flexible, and the shape tolerance is large; the insertion phase of the wave can be changed, special phase wavefront correction is completed in an optical system, and the bandwidth of the scanning antenna is widened. Therefore, the lens antenna is widely applied to the fields of satellite communication systems, millimeter wave radar measurement and imaging systems, even biomedicine and the like.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to realize an impedance matching high-gain lens antenna with a directional beam on an H surface and an omnidirectional beam on an E surface. The antenna has the characteristics of wide working frequency band, small loss, high gain, good far-field directionality, low sidelobe level and the like.
The technical scheme is as follows: in order to realize the purpose, the invention adopts the following technical scheme:
an impedance matching high-gain lens antenna comprises an impedance matching lens and an H-face fan-shaped horn antenna loaded with a waveguide extension section, wherein the caliber of the H-face fan-shaped horn antenna is connected with the waveguide extension section with the same caliber size, the length of the waveguide extension section is equal to the thickness of the impedance matching lens, the impedance matching lens is embedded in the waveguide extension section, and the side face of the impedance matching lens is fixedly connected with the inner side wall of the waveguide extension section.
Optionally, the size of the H-plane sectorial horn antenna loaded with the waveguide extension section is related to the refractive index distribution of the impedance matching lens, and the specific size is obtained according to a design formula of the impedance matching lens.
Optionally, the refractive index distribution of the impedance matching lens shows a non-linear decreasing rule change from the central point to the periphery, and the refractive index around the lens is 1.
Optionally, the impedance matching lens includes a plurality of basic unit structures, the basic unit structures having the same equivalent refractive index are correspondingly arranged according to the overall refractive index distribution of the impedance matching lens, a cylindrical through hole is etched in the center of the basic unit structure, the equivalent refractive index of the unit structure is changed by changing the size of the aperture R, and the equivalent refractive index of the unit structure is closer to air as the aperture R is larger.
Optionally, the basic cell structure is an isotropic structure.
Optionally, the cell structure is implemented by using three dielectric constant materialsRespectively is a dielectric constant εrTP-2 having a loss tangent of 0.03 and a dielectric constant ε (7)rFR-4 with a loss tangent of 0.025 at 4.3 and a dielectric constant εrF4B with a loss tangent σ of 0.001 of 2.2.
The invention also provides a design method of the impedance matching high-gain lens antenna, which comprises the following steps:
(1) designing an H-face sectorial horn antenna loaded with a waveguide extension section, reasonably setting the caliber size and the focal length of the H-face sectorial horn antenna according to a calculation method of the refractive index distribution of an impedance matching lens, and setting the length of the waveguide extension section of the H-face sectorial horn antenna to be equal to the width of the impedance matching lens in order to ensure the complete fixation of the impedance matching lens;
(2) designing an impedance matching lens, and obtaining the overall refractive index distribution of the impedance matching lens according to the caliber size of the H-plane sector horn antenna and the length of the waveguide extension section by combining a calculation method of the refractive index distribution of the impedance matching lens;
(3) designing a basic unit structure of the impedance matching lens, etching a cylindrical through hole in the center of the basic unit structure, and changing the equivalent refractive index of the unit structure by changing the size of the aperture R; correspondingly arranging basic units with the same equivalent refractive index according to the overall refractive index distribution of the impedance matching lens so as to form a final impedance matching lens;
(4) and completely embedding the impedance matching lens into the waveguide extension section at the front end of the H-plane sectorial horn antenna to form the impedance matching high-gain lens antenna.
Further, the method for calculating the refractive index distribution of the entire impedance matching lens is as follows: according to the Fermat theorem, the optical paths from any light ray to the surface of the lens from a point source are the same; thus, there are:
assuming that the lens varies in both the x and y directions, the above equation transforms to:
when Δ y → 0, the above equation is simplified to:
after integrating y, it becomes:
it is clear that the left side of the equation is only a function of the variable y and the geometric parameter t, so the left side of the equation is further simplified as:
if the lens varies only in the y-direction, the refractive index profile is:
the lens refractive index profile also varies linearly along the x-direction, then:
wherein n ismaxIs the maximum value of the refractive index of the lens;
wherein:
nmax＝2n(y)-1 (9)；
therefore, for a two-dimensionally varying impedance-matched lens, given appropriate parameters according to equations (7) - (9), the refractive index distribution of the entire impedance-matched lens is obtained.
Has the advantages that: compared with the prior art, the invention has the following advantages:
1. the loss is small: the invention consists of an impedance matching lens and an H-plane sector horn antenna loaded with a waveguide extension section, wherein the refractive index of the periphery of the impedance matching lens is 1, and the impedance matching lens can be perfectly matched with a free space without additionally designing a matching layer, so that the reflection of electromagnetic waves on the surface of the lens is reduced.
2. The far field directionality is good: compared with an H-plane sector horn antenna, the invention corrects the wave front phase of the electromagnetic wave, and the emergent electromagnetic wave is a plane wave, so that the far field directionality of the electromagnetic wave is improved.
3. High gain, low sidelobe level: compared with an H-face sector horn antenna, under the condition of the same caliber, the gain of the antenna is obviously improved, the lobe width of the H face is narrowed, the level of the side lobe is obviously reduced, and the E face has better omni-directionality.
4. The size is small: compared with the traditional H-plane optimal horn antenna, the phase center-to-aperture plane distance is shorter under the same aperture plane condition.
5. The working frequency bandwidth is wide: the invention is made of isotropic material, is insensitive to the incident direction of electromagnetic wave and has wide working bandwidth.
Drawings
FIG. 1 is a schematic design of an impedance matched lens;
FIG. 2 is a refractive index profile of an impedance matched lens;
FIG. 3 is a unit structure view of an impedance matching lens;
fig. 4 is a graph of equivalent refractive index of the impedance matching lens cell structure as a function of the radius of the aperture. Three lines from high to low respectively represent three materials of TP-2, FR-4 and F4B;
FIG. 5 is an overall schematic diagram of an impedance matching lens;
fig. 6 is a near field distribution diagram of an H-plane sectored horn antenna;
FIG. 7 is a near field profile of an impedance matched high gain lens antenna;
FIG. 8 is a near field profile of an H-plane lens antenna loaded with a common lens;
FIG. 9 is a phase profile on the aperture side of a lens antenna; the solid line is the phase distribution of the impedance matching high-gain lens, and the dotted line is the phase distribution of the H-plane lens antenna loaded with the common lens;
fig. 10 is a far field pattern (H-plane) of an H-plane sectored horn antenna; the solid line represents the simulation result, and the dotted line represents the test result;
FIG. 11 is a far field pattern (H-plane) of an impedance matched high gain lens antenna; the solid line represents the simulation result, and the dotted line represents the test result;
FIG. 12 is a graph of the results of an impedance matched high gain lens antenna S11 test;
FIG. 13 is a graph of far field pattern (E-plane) test results; the solid line represents an impedance-matched high-gain lens antenna, and the dotted line represents an H-plane sectorial horn antenna;
FIG. 14 is a gain test chart for an X-band antenna; the square lines represent the impedance matched lens high gain antenna and the dot lines represent the H-plane sectored horn antenna.
Detailed Description
The invention is further described with reference to specific embodiments and the accompanying drawings.
An impedance matching high-gain lens antenna comprises an impedance matching lens and an H-face sector horn antenna loaded with a waveguide extension section, wherein the caliber of the H-face sector horn antenna is connected with the waveguide extension section with the same caliber size and used for fixing the impedance matching lens; the length of the waveguide extension segment is equal to the thickness of the impedance matching lens, and the waveguide extension segment is used for fixing the impedance matching lens and completely covering the side face of the impedance matching lens. An electromagnetic wave signal excited by a signal source is radiated to a cylindrical wave through an H-plane sector horn antenna, the cylindrical wave is corrected in phase through an impedance matching lens, and the cylindrical wave is converted into a two-dimensional plane wave with an equiphase plane perpendicular to the propagation direction and finally radiated to a free space. The refractive index of the impedance matching lens changes in a nonlinear mode along the x direction and the y direction, the refractive index around the impedance matching lens is 1, and the impedance matching lens can be perfectly matched with a free space. The invention has the advantages of wide band and low loss, and can work normally in X wave band. In the X wave band, compared with an H-plane sector horn antenna, the gain of the invention is improved, and the improvement range is 5.7-7.2 dB.
The impedance matching lens comprises a plurality of basic unit structures, the refractive index distribution of the whole lens is obtained according to a refractive index distribution calculation method of the impedance matching lens, and basic units with the same equivalent refractive index are correspondingly arranged according to the refractive index distribution of the impedance matching lens, so that the final impedance matching lens is formed. The center of the basic unit structure is etched with a cylindrical through hole, the equivalent refractive index of the unit structure is changed by changing the size of the aperture R, and the equivalent refractive index of the unit structure is closer to air as the aperture R is increased.
The impedance matching lens adopts an isotropic structure as a basic unit. The invention adopts a medium perforating structure as a basic structural unit of the lens. The equivalent refractive index of the unit structure is changed by etching the cylindrical through hole on the original dielectric block and changing the aperture R so as to meet the design requirement. The relationship between the aperture R and the equivalent refractive index variation of the unit structure roughly follows: as the aperture R becomes larger, the equivalent refractive index of the unit structure becomes closer to air. The unit has the advantages that: 1. because the size of the dielectric blocks is far smaller than the wavelength, when the dielectric blocks with designed parameters are assembled together, the discrete parameter distribution can well simulate the continuous parameter distribution of natural materials; 2. the punching structure does not change the electromagnetic parameters by utilizing the resonance principle, so the punching structure has the inherent advantages which are not possessed by a metal structure, such as broadband characteristics, low loss and the like; 3. the punched structure is used as an isotropic structural unit, the electromagnetic characteristics in different directions are basically consistent, and the punched structure is insensitive to the incident direction of electromagnetic waves and applicable to large-angle incidence.
A design method of an impedance matching high gain lens antenna comprises the following steps:
(1) designing an H-face sectorial horn antenna loaded with a waveguide extension section, reasonably setting the caliber size and the focal length of the H-face sectorial horn antenna according to a calculation method of the refractive index distribution of an impedance matching lens, and setting the length of the waveguide extension section of the H-face sectorial horn antenna to be equal to the width of the impedance matching lens in order to ensure the complete fixation of the impedance matching lens;
(2) designing an impedance matching lens, and obtaining the overall refractive index distribution of the impedance matching lens according to the caliber size of the H-plane sector horn antenna and the length of the waveguide extension section by combining a calculation method of the refractive index distribution of the impedance matching lens;
(3) designing a basic unit structure of the impedance matching lens, etching a cylindrical through hole in the center of the basic unit structure, and changing the equivalent refractive index of the unit structure by changing the size of the aperture R. Correspondingly arranging basic units with the same equivalent refractive index according to the overall refractive index distribution of the impedance matching lens so as to form a final impedance matching lens;
(4) and completely embedding the impedance matching lens into the waveguide extension section at the front end of the H-plane sectorial horn antenna to form the impedance matching high-gain lens antenna.
The schematic diagram of the impedance matching lens is shown in fig. 1, two light sources are emitted from a point source, and an emergent wave is a plane wave after passing through a plane lens. The method for calculating the refractive index distribution of the entire impedance matching lens is as follows: according to the Fermat's theorem, any ray from a point source travels the same optical path to the lens surface. Thus, there are:
wherein the thickness of the lens is t, the vertical distance from the point source to the impedance matching lens is f, n1Is the refractive index of air, n (x, y) is the equivalent refractive index of the lens at position (x, y), l1，l2，l3，l4Respectively, the paths of the two light sources passing through the two sides of the lens.
Unlike conventional design methods, we assume that the lens varies in both the x and y directions, and equation (1) transforms to:
when Δ y → 0, equation (2) reduces to:
after integrating y, it becomes:
it is clear that the left side of the equation is only a function of the variable y and the geometric parameter t, so the left side of the equation is further simplified as:
if the lens varies only in the y-direction, the refractive index profile is:
one of the characteristics of the lens is that the refractive index increases from the edge to the center along the x-direction, e.g. the lens refractive index profile also varies linearly along the x-direction, then:
wherein n ismaxIs the maximum value of the refractive index of the lens;
wherein:
nmax＝2n(y)-1 (9)；
therefore, for an impedance-matched lens that varies in two dimensions (the refractive index varies in both the x and y directions), the refractive index distribution of the entire impedance-matched lens can be obtained, given appropriate parameters, according to equations (7) - (9). The derivation of the formula shows that the refractive index of the impedance matching lens is changed from the central point to the periphery in a nonlinear decreasing rule, the refractive index at the periphery is 1, a matching layer is not required to be additionally designed, the impedance matching lens can be perfectly matched with a free space, and the reflection of electromagnetic waves is obviously reduced.
The size of the H-face sectorial horn antenna loaded with the waveguide extension section is related to the refractive index distribution of the impedance matching lens, and the specific size can be obtained according to the design formulas (7) to (9) of the impedance matching lens.
To further explain the design process of the impedance matching high-gain lens antenna, taking an impedance matching high-gain lens H-plane horn antenna as an example, the focal length of the impedance matching lens is set to be 7 wavelengths, which is equal to the distance from the phase center of the H-plane sectoral horn antenna to the aperture plane; setting the length of the lens to be 10 wavelengths, wherein the length of the lens is equal to the length of an upper caliber of an H surface of the horn antenna; the thickness of the impedance matching lens is set to be 2 wavelengths, and the length of the impedance matching lens is equal to the length of a waveguide extension section at the aperture surface of the H-face fan-shaped horn antenna. The specific performance parameters of the impedance matching high-gain lens H-plane horn antenna are as follows:
to verify the effect of the impedance matching lens, we combined the H-plane sectored horn antenna aperture plane lengthened and the impedance matching lens, and simulated it in the commercial software CST. The length of the lens is 300mm (10 wavelengths), the width of the lens is 60mm (2 wavelengths), and the distance from the phase center of the antenna to the aperture surface of the impedance matching lens is 210 mm. The refractive index distribution of the impedance matching lens is shown in formula (7), and the center frequency is 10 GHz. The maximum refractive index n is selected in consideration of the realizability of the devicemaxThe refractive index profile of the impedance matched lens is shown in fig. 2, 2.6. Obviously, the refractive index of the lens is distributed from the center point to the periphery in a ring shape, and the refractive index of the most marginal part is 1, so that the lens can be perfectly matched with a free space.
The impedance matching lenses are all composed of a non-homogeneous medium. Based on the characteristics of the material, a medium punching structure is adopted as a basic structural unit of the lens. As shown in fig. 3, the structural unit size a is 3mm, which is about one tenth of a wavelength. The dielectric constant of the unit structure is changed by etching the cylindrical through hole on the original dielectric block and changing the aperture R, so that the required electromagnetic property is realized. The relationship between the aperture R and the equivalent refractive index variation of the unit structure roughly follows: as the aperture R becomes larger, the equivalent refractive index of the unit structure becomes closer to air. Because the size of the dielectric blocks is far smaller than the wavelength, when the dielectric blocks with designed parameters are assembled together, the discrete parameter distribution can well simulate the continuous parameter distribution of natural materials. Secondly, the electromagnetic parameters of the perforated structure are not changed by utilizing the resonance principle, so that the perforated structure has the inherent advantages which are not possessed by the metal structure, such as broadband characteristics, low loss and the like. Most importantly, the perforating structure is used as an isotropic structural unit, the electromagnetic characteristics in different directions are basically consistent, and the perforating structure is insensitive to the incident direction of electromagnetic waves and suitable for large-angle incidence.
To cover the refractive index range of 1-2.6, we have chosen three materials with dielectric constants, εrTP-2 having a loss tangent of 0.03 and a dielectric constant ε (7)rFR-4 with a loss tangent of 0.025 at 4.3 and a dielectric constant εrF4B with a loss tangent σ of 0.001 of 2.2. In the design process, three materials are functionally divided: the relative dielectric constant of 4 to 7 is partly defined by ∈rTP-2 punching of which is 7; the relative dielectric constant of 2.2 to 4 is partially defined by ∈rFR-4 of 4.3 is punched; the part with relative dielectric constant between 1 and 2.2 is composed of ∈rF-4B perforation 2.2. The variation relationship between the equivalent refractive index and the aperture R size of the unit structure of the three materials is shown in FIG. 4. As can be seen, even for εrThe minimum achievable refractive index is only about 1.25 for the F-4B material of 2.2. The index of refraction of the outermost periphery of the impedance matched lens is not matched to 1 but to 1.25, which adds some unwanted reflections between the lens and the air. The method is limited by the existing processing precision, and the aperture of the punched hole can only be integral multiple of 0.05mm, so that the aperture is further approximated in the processing process.
The invention is wholly simulated by using commercial software CST, and the structural schematic diagram is shown in FIG. 5. To verify the correction of the wavefront phase of the cylindrical wave by the impedance matching lens, the near field profile of the antenna was analyzed using a field monitor in CST. Fig. 6 is a near-field distribution diagram of the H-plane sectoral horn antenna, and it is apparent that the emergent wave is a cylindrical wave structure. Fig. 7 is a diagram of the near field distribution of an impedance matched high gain lens antenna after loading the impedance matched lens, where the cylindrical wave is effectively converted into a planar wave due to the correction of the wavefront phase by the impedance matched lens, and the reflection of the incident wave and the reflected wave is small due to the lens edge impedance being approximately 1. Fig. 8 shows the near-field distribution of an H-plane lens antenna loaded with a normal lens, where the refractive index of the lens changes only in the y-direction and remains unchanged in the wave propagation direction (x-direction) as shown in equation (6). Thus, compared to the present invention (fig. 7), the normal lens (fig. 8) has a larger reflection for both incident and reflected waves. For further comparison, we plot the phase change of the electric field in the y direction at 30mm from the aperture plane in the x direction, as shown in fig. 9. The solid line represents the phase distribution of the impedance-matched lens, and the dotted line represents the electric field phase distribution of the normal lens. It is clear that the impedance matched lens antenna reflects less at the aperture plane and the phase change is more uniform. The above near-field simulation is a simulation based on a real unit structure.
We also simulated the far field pattern of the antenna of the present invention using a field monitor, as shown by the solid lines in fig. 10 and 11. Wherein, the solid line in fig. 10 is the H-plane far-field pattern of the H-plane sectoral horn antenna, the simulation gain G is 11.6dB, and the side lobe level SLL is 5 dB; and the solid line in fig. 11 shows the H-plane far-field pattern of the impedance-matched high-gain lens antenna after loading the impedance-matched lens, the simulated gain is increased to G17.9 dB, and the side lobe level is decreased to SLL 15 dB. Obviously, after the impedance matching lens is loaded, the H-plane far-field characteristic of the antenna is obviously improved.
In order to further verify the function of the impedance matching high-gain lens antenna, an H-plane sectorial horn antenna is customized, the phase center of the antenna is just positioned at the focal position of an impedance matching lens, and the outer end of the aperture surface of the H-plane sectorial horn antenna is extended to a certain extent and used for placing the impedance matching lens antenna. In order to simplify the processing steps of the impedance matching lens, the impedance matching lens antenna is cut along the direction of an x axis and is equally divided into 19 layers, each layer is made of one or more of the three materials, through holes with corresponding sizes are etched according to the overall refractive index distribution of the impedance matching lens, and different materials are bonded. Finally, combining the overall refractive index distribution of the impedance matching lens, the impedance matching lens is formed by bonding the 19 layers of perforated dielectric plates along the x-axis direction, is arranged in the extended aperture surface of the H-surface sectorial horn antenna, and is combined into the impedance matching high-gain lens antenna.
Through testing, the reflection coefficient S11 of the impedance matching high-gain lens antenna is less than-10 dB in the whole X wave band (8-12GHz), as shown in figure 12. This shows that the lens antenna designed by us can work normally in the X-band. The dotted lines in fig. 10 and 11 represent the test results of the H-plane far-field pattern of the antenna. The gain of the H-plane sectorial horn antenna is 11.2dB, the width of an H-plane half-power lobe is 36.5 degrees, and the level of a side lobe is 5.8 dB; after the impedance matching lens is loaded, the gain of the impedance matching high-gain lens antenna is improved to 17.7dB, the width of an H-plane half-power lobe is reduced to 6.2 degrees, and the level of a side lobe is reduced to 15.3 dB. The test result is well matched with the simulation result.
We also tested the E-plane far field pattern of an impedance matched high gain lens antenna, the results of which are shown in fig. 13. As can be seen from the figure, after the impedance matching lens is loaded, compared with the H-plane sectoral horn antenna, the field pattern on the E plane is unchanged, but the gains are both improved, and the omnidirectional characteristic is presented.
The gain variation curve of the present invention in the X band is shown in fig. 14, in which the square line represents the gain variation curve of the H-plane sectoral horn antenna without loading the impedance matching lens, and the dot line represents the gain variation curve of the impedance matching high gain lens antenna after loading the impedance matching lens. It can be seen from the figure that the gain of the antenna is significantly improved after loading the impedance matching lens in the whole X-band, and the improvement range is 5.7-7.2 dB. The designed impedance matching lens remarkably improves the performance of the H-plane sectored horn antenna.
In addition, we compare the present invention with a conventional H-plane optimal horn antenna. According to the traditional antenna design theory, the caliber length D of the H-plane optimal horn antenna in the H-plane direction and the distance f from the antenna phase center to the caliber surface satisfy the following relation,
under the condition, the gain of the antenna is highest, and the aperture surface efficiency eta of the H-surface optimal horn antenna at the momenta0.64. Assuming that the radiation efficiency η of the antenna is 100%, the gain calculation formula is as follows:
wherein a represents the physical aperture plane size of the antenna.
The distance f from the phase center to the aperture of the H-plane optimal horn antenna is 1000mm, which is about 5 times the distance (210mm) from the phase center to the aperture of the present invention, under the same aperture size. According to the formula (11), calculating the gain G of the H-plane optimal horn antenna to be 16 dB; the test result of the gain of the invention is 17.7dB, which is 1.7dB higher than the traditional H-plane optimal horn antenna. In addition, test results show that the aperture surface efficiency of the invention is 94%, which is much higher than that of the traditional H-plane optimal horn antenna.
The above examples are only preferred embodiments of the present invention, it should be noted that: it will be apparent to those skilled in the art that various modifications and equivalents may be made without departing from the spirit of the invention, such as changing the size of the H-plane sectoral horn antenna, or replacing the H-plane sectoral horn antenna with another antenna, and such modifications and equivalents may fall within the scope of the invention as defined in the appended claims.
Claims (6)
1. A design method of an impedance matching high-gain lens antenna is characterized in that the impedance matching high-gain lens antenna comprises an impedance matching lens and an H-face fan-shaped horn antenna loaded with a waveguide extension section, the impedance matching lens comprises a plurality of basic unit structures, basic unit structures with the same equivalent refractive index are correspondingly arranged according to the overall refractive index distribution of the impedance matching lens, a cylindrical through hole is etched in the center of each basic unit structure, the equivalent refractive index of each basic unit structure is changed by changing the size of an aperture R, and the equivalent refractive index of each basic unit structure is closer to the air as the size of the aperture R is increased; the aperture of the H-face sector horn antenna is connected with a waveguide extension section with the same aperture size, the length of the waveguide extension section is equal to the thickness of the impedance matching lens, the impedance matching lens is embedded in the waveguide extension section, and the side face of the impedance matching lens is fixedly connected with the inner side wall of the waveguide extension section;
the design method comprises the following steps:
(1) designing an H-face sectorial horn antenna loaded with a waveguide extension section, reasonably setting the caliber size and the focal length of the H-face sectorial horn antenna according to a calculation method of the refractive index distribution of an impedance matching lens, and setting the length of the waveguide extension section of the H-face sectorial horn antenna to be equal to the width of the impedance matching lens in order to ensure the complete fixation of the impedance matching lens;
(2) designing an impedance matching lens, and obtaining the overall refractive index distribution of the impedance matching lens according to the caliber size of the H-plane sector horn antenna and the length of the waveguide extension section by combining a calculation method of the refractive index distribution of the impedance matching lens;
(3) designing a basic unit structure of the impedance matching lens, wherein a cylindrical through hole is etched in the center of the basic unit structure, and the equivalent refractive index of the basic unit structure is changed by changing the size of an aperture R; correspondingly arranging basic unit structures with the same equivalent refractive index according to the overall refractive index distribution of the impedance matching lens so as to form a final impedance matching lens;
(4) and completely embedding the impedance matching lens into the waveguide extension section at the front end of the H-plane sectorial horn antenna to form the impedance matching high-gain lens antenna.
2. The method of claim 1, wherein the refractive index profile of the entire impedance-matched lens is calculated by: according to the Fermat theorem, the optical paths from any light ray to the surface of the lens from a point source are the same; thus, there are:
wherein t is the thickness of the lens, f is the vertical distance from the point source to the impedance matching lens, n1Is the refractive index of air, n (x, y) is the equivalent refractive index of the lens at position (x, y); l2，l4Respectively the paths passed by the two light sources after entering the lens;
assuming that the lens varies in both the x and y directions, the above equation transforms to:
when Δ y → 0, the above equation is simplified to:
after integrating y, it becomes:
wherein n iscIs the equivalent refractive index at the center of the lens; it is clear that the left side of the equation is only a function of the variable y and the geometric parameter t, so the left side of the equation is further simplified as:
where n (y) is the equivalent refractive index of the lens in the y-direction; if the lens varies only in the y-direction, the refractive index profile is:
the lens refractive index profile also varies linearly along the x-direction, then:
wherein n ismaxIs the maximum value of the refractive index of the lens;
wherein:
nmax＝2n(y)-1 (9)；
therefore, for a two-dimensionally varying impedance-matched lens, given appropriate parameters according to equations (7) - (9), the refractive index distribution of the entire impedance-matched lens is obtained.
3. The method as claimed in claim 1, wherein the dimension of the H-plane sectoral horn antenna loaded with the waveguide extension is related to the refractive index distribution of the impedance matching lens, and the specific dimension is obtained according to the design formula of the impedance matching lens.
4. The method as claimed in claim 1, wherein the refractive index distribution of the impedance-matched lens varies in a non-linear decreasing manner from the center to the periphery, and the refractive index around the lens is 1.
5. The method of claim 1, wherein the basic cell structure is an isotropic structure.
6. The method of claim 1, wherein the basic unit structure is implemented by using three dielectric constant materials, respectively dielectric constant εrTP-2 having a loss tangent of 0.03 and a dielectric constant ε (7)rFR-4 with a loss tangent of 0.025 at 4.3 and a dielectric constant εrF4B with a loss tangent σ of 0.001 of 2.2.
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