CN110380230B - Ultra-wideband high-gain lens antenna based on three-dimensional impedance matching lens and design method thereof - Google Patents
Ultra-wideband high-gain lens antenna based on three-dimensional impedance matching lens and design method thereof Download PDFInfo
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Abstract
The invention discloses an ultra-wideband high-gain lens antenna based on a three-dimensional impedance matching lens and a design method thereof. Coherent electromagnetic waves emitted from a high-frequency signal source radiate spherical waves through the double-ridged horn antenna, are converted into non-uniform plane waves with an equiphase plane orthogonal to the propagation direction through the three-dimensional impedance matching lens fixed in the extension section of the horn antenna aperture surface waveguide, and radiate to a free space. The lens antenna is easy to design, simple in structure, low in cost, wide in working frequency band, high in gain and small in return loss, can replace a traditional uniform medium lens antenna, and has a high application value in many fields.
Description
Technical Field
The invention relates to an ultra-wideband high-gain three-dimensional impedance matching lens antenna and a design method thereof, belonging to the field of novel artificial electromagnetic devices.
Background
The horn antenna is characterized by that the end of feed waveguide section is gradually opened at a certain angle, mostly circular or rectangular mouth surface, and its whole form is horn-shaped, so that it is one of the most popular microwave devices. The horn antenna is widely used because of its advantages of simple structure, wide operating frequency band, large power capacity, low return loss, low insertion loss, etc. However, to obtain better directivity or higher gain, it must have a larger size, which also limits its practical application in many situations. In order to obtain the same performance in a smaller size, a dielectric material can be made into a certain shape based on the geometric optics theory and placed on the opening surface of the horn antenna to form a lens antenna so as to converge electromagnetic wave signals, form a narrower wave beam and improve the directionality of the horn antenna. However, most of the existing lenses are made of uniform dielectric materials, and exhibit a predetermined shape through machining, and the large volume, high machining precision and high cost of the existing lenses are short plates which limit the wide application of the lenses.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to realize an ultra-wideband high-gain lens antenna which has the advantages of simple structure, low cost, wide working frequency band, good directionality and low return loss.
The technical scheme is as follows: in order to realize the purpose, the invention adopts the following technical scheme:
the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens comprises the three-dimensional impedance matching lens, the double-ridge horn antenna and a waveguide extension section, wherein an opening of the double-ridge horn antenna is connected with the waveguide extension section, the three-dimensional impedance matching lens is embedded in the waveguide extension section, and the length of the waveguide extension section is equal to the thickness of the three-dimensional impedance matching lens so as to completely cover the side edge of the three-dimensional impedance matching lens.
Optionally, the three-dimensional impedance matching lens has a certain thickness, and the shape of the three-dimensional impedance matching lens is consistent with the shape of the horn antenna aperture.
Optionally, the three-dimensional impedance matching lens includes a plurality of equivalent refractive index units, and the equivalent refractive index units include two types, wherein one type includes a pair of perforated dielectric substrates and a dielectric substrate with a square metal patch covered on both sides, and the pair of perforated dielectric substrates are symmetrically attached to both sides of the dielectric substrate with metal covered on both sides; the other type of the punching medium substrate comprises three punching medium substrates, wherein the punching sizes of two punching medium substrates are fixed and equal, and the two punching medium substrates which are fixed and have equal sizes are symmetrically clung to two sides of the rest punching medium substrate.
Optionally, the equivalent refractive index subsections of the three-dimensional impedance matching lens are in gradual change distribution in three orthogonal directions of x, y and z, the gradual change distribution decreases from the center to two sides, and along the propagation direction of the electromagnetic wave, the equivalent refractive indexes at two ends of the lens are 1 and are completely matched with the free space.
Optionally, the double-ridged horn antenna is a broadband horn antenna, and radiates broadband spherical waves as a feed source, and the working bandwidth of the lens antenna depends on the working bandwidth of the double-ridged horn antenna.
The invention also provides a design method of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens, which comprises the following steps:
(1) designing a double-ridge horn antenna and a waveguide extension section;
the double-ridge horn antenna is a double-ridge pyramid horn antenna with a square opening surface, the extending part of the horn opening surface is a waveguide extension section, the diameter surface of the horn opening is set according to a three-dimensional impedance matching lens design formula, and the length of the waveguide extension section is set for ensuring that the waveguide extension section completely covers the side edge of the three-dimensional impedance matching lens;
(2) designing a three-dimensional impedance matching lens;
considering a square opening surface of the double-ridged pyramid horn antenna, setting the three-dimensional impedance matching lens to be in a cuboid shape, and setting the length, the width and the thickness of the three-dimensional impedance matching lens according to a design formula of the three-dimensional impedance matching lens; the three-dimensional impedance matching lens comprises a plurality of equivalent refractive index units, wherein the equivalent refractive index units comprise two types: one type comprises a pair of perforated medium substrates and a medium substrate with two sides covered by a square metal patch, wherein the pair of perforated medium substrates are symmetrically clung to two sides of the medium substrate with two sides covered by metal; one type of the medium base plate comprises three punching medium base plates, wherein the punching sizes of two punching medium base plates are fixed and equal, and the two punching medium base plates which are fixed and have equal sizes are symmetrically clung to two sides of the rest punching medium base plate.
Further, the specific design steps of the equivalent refractive index unit are as follows:
(21) calculating and extracting discrete equivalent refractive index distribution of the three-dimensional matched lens by using Matlab software, wherein the discrete interval in the x direction and the y direction is about 0.1 wavelength, the discrete interval in the z direction is about 0.06 wavelength, and a three-dimensional matrix corresponding to the lens equivalent refractive index distribution is obtained, wherein the wavelength is specified as the central wavelength of the double-ridge horn antenna;
(22) considering that the discrete spacing of the three-dimensional matched lens in the x and y directions is about 0.1 wavelength, and the discrete spacing in the z direction is about 0.06 wavelength, the equivalent refractive index unit size is set to be about 0.1 wavelength in the x and y directions, and about 0.06 wavelength in the z direction; one type of the two equivalent refractive index units adjusts the equivalent refractive index by changing the side lengths of two layers of square metal patches in the equivalent refractive index units; the equivalent refractive index of the first type is adjusted by changing the size of the hole punched in the middle layer of the equivalent refractive index unit; when two types of equivalent refractive index units are designed, the adopted dielectric substrate is a Teflon sheet material with the dielectric constant of 2.2 and the loss tangent of 0.0001, and the metal patch is made of pure copper;
(23) and correspondingly arranging equivalent refractive index units with different sizes according to the equivalent refractive index three-dimensional matrix to form the cuboid three-dimensional impedance matching lens.
Further, the method for calculating the equivalent refractive index distribution of the whole lens comprises the following steps:
according to the Fermat's theorem, in order to ensure that the emergent wave is a plane wave with equal phase, it is necessary to ensure that the total optical path of any electromagnetic wave radiated from a point source is equal after passing through a free space and a lens; therefore, assuming that the center of the lens is the origin of the coordinate axis, and the direction of the line from the point source to the center of the lens is the z direction, for any point (x, y, z) on the lens, there are:
wherein n is1Is the free space refractive index; t is the thickness of the lens, and f is the vertical distance from the point source to the edge of the lens;
unlike other lenses, the equivalent refractive index of the three-dimensional impedance matching lens is gradually changed from the center to two sides in the three orthogonal directions x, y and z, and for convenience, the three-dimensional impedance matching lens is assumed to be linearly changed in the three orthogonal directions, so that the above formula is changed as follows:
order to
The above formula is simplified as follows:
integrating the above equation, the equation becomes:
when z is fixed, the above equation reduces to:
assuming that the equivalent refractive index of the lens has the same linear variation trend in the x and y directions, there are:
assuming that the equivalent refractive index of the lens on both sides in the z direction should be 1, and the equivalent refractive index of the lens varies with decreasing linear center, therefore:
substituting the above equation into equation (5), then:
wherein n ism(0) Is the maximum value of the equivalent refractive index of the lens;
assuming that the equivalent refractive index varies linearly, therefore:
nm(z)＝2n(x，y)-1 (9)；
therefore, according to equations (7), (8), and (9), the equivalent refractive index distribution of the entire lens is obtained.
Has the advantages that: compared with the prior art, the invention has the following advantages:
1. easy design: the three-dimensional impedance matching lens is quickly designed according to the existing formula, is suitable for different application scenes, and only needs to adjust parameters in the formula according to different application scenes.
2. Simple structure, low cost: the three-dimensional impedance matching lens is formed by stacking the microwave dielectric plates, can be processed by a PCB process, and has the advantages of low design difficulty, low precision requirement and low cost.
3. The working frequency bandwidth is wide: the equivalent refractive index unit adopted by the invention has a flat refractive index curve, can work in a very wide frequency band, the working bandwidth of the lens antenna only depends on the bandwidth of the double-ridge horn antenna serving as the feed source, and the double-ridge horn antenna can be replaced by other types of broadband horn antennas.
4. High gain and good directionality: the mechanism of the invention is that coherent electromagnetic waves emitted from a high-frequency signal source are converted into non-uniform plane waves with an equiphase surface orthogonal to a propagation direction to radiate to a free space through a three-dimensional impedance matching lens in a waveguide extension section fixed on the mouth surface of the horn antenna by radiating spherical waves through the double-ridge horn antenna, so that the far field has good directionality and high gain.
5. The return loss is low: the equivalent refractive index of the three-dimensional impedance matching lens is gradually distributed in the x, y and z orthogonal directions in a mode that the refractive index decreases from the center to two sides, particularly in the z direction of electromagnetic wave propagation, the equivalent refractive index of two ends of the lens is 1, the lens is completely matched with a free space, electromagnetic wave reflection does not exist, and therefore a matching layer does not need to be added or other technologies are adopted to reduce return loss of an antenna.
Drawings
Fig. 1 is a schematic diagram of an ultra-wideband high gain lens antenna structure based on a three-dimensional impedance matching lens;
FIG. 2 is a schematic diagram of a double-ridged pyramid horn antenna structure with waveguide extensions added;
FIG. 3 is a schematic diagram of a coaxial-double ridge waveguide transition structure;
FIG. 4 is a graph of-10 dB return loss simulation results for a double-ridged pyramidal horn antenna with an added waveguide extension;
FIG. 5 is an equivalent refractive index distribution diagram of a three-dimensional impedance-matched lens in the shape of a rectangular parallelepiped;
FIG. 6 is a schematic diagram of an equivalent refractive index unit structure containing a double-sided covered square metal patch;
FIG. 7 is a schematic diagram of an equivalent refractive index unit structure comprising three layers of perforated dielectric substrates;
FIG. 8 is a schematic diagram of the structure of layers 1-3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29-31 of the three-dimensional impedance matching lens;
FIG. 9 is a schematic diagram of the structure of the 4 th and 28 th layers of the three-dimensional impedance matching lens;
FIG. 10 is a schematic diagram of the structure of the layers 6 and 26 of the three-dimensional impedance matching lens;
FIG. 11 is a schematic diagram of the structure of the 8 th and 24 th layers of the three-dimensional impedance matching lens;
FIG. 12 is a schematic diagram of the structure of the 10 th and 22 th layers of the three-dimensional impedance matching lens;
FIG. 13 is a schematic diagram of the structure of the 12 th and 20 th layers of the three-dimensional impedance matching lens;
FIG. 14 is a schematic diagram of the structure of the 14 th and 18 th layers of the three-dimensional impedance matching lens;
FIG. 15 is a schematic diagram of a 16 th layer structure of a three-dimensional impedance matching lens;
FIG. 16 is a graph of ultra-wideband high gain lens antenna-10 dB return loss simulation results based on a three-dimensional impedance matching lens;
fig. 17 is a graph comparing the gain results for an ultra-wideband high gain lens antenna based on a three-dimensional impedance matching lens and a double-ridged pyramid horn antenna not loaded with a three-dimensional impedance matching lens.
Detailed Description
The technical solution of the present invention will be further described with reference to the following embodiments and accompanying drawings. The following examples are only preferred embodiments of the present invention, it being noted that: for those skilled in the art, without departing from the principle of the present invention, several modifications and equivalents may be made, such as changing the size and shape of the three-dimensional matching lens, changing the equivalent refractive index distribution rule of the three-dimensional impedance matching lens, or replacing the double-ridged pyramid horn antenna with other broadband antennas, and these modifications and equivalents of the claims of the present invention fall within the scope of the present invention.
A ultra-wideband high-gain lens antenna based on a three-dimensional impedance matching lens is shown in figure 1 and comprises a three-dimensional impedance matching lens 1 in a cuboid shape, a square opening face double-ridge pyramid horn antenna feed source 2 and a waveguide extension section 3, wherein an opening of the double-ridge horn antenna is connected with the waveguide extension section, the three-dimensional impedance matching lens is embedded in the waveguide extension section, and the length of the waveguide extension section is equal to the thickness of the three-dimensional impedance matching lens so as to completely cover the side edge of the three-dimensional impedance matching lens.
A double-ridged pyramid horn antenna with the addition of a waveguide extension is shown in fig. 2. Coherent electromagnetic waves emitted from a high-frequency signal source are coaxially fed into the double-ridged pyramid horn antenna and are converted into spherical-like waves through the coaxial-double-ridged waveguide conversion structure 11. The side view of the coaxial-double-ridge waveguide conversion structure is shown in fig. 3, two ridges 4 are symmetrically connected with the upper and lower parts of the inner wall of a waveguide section at the rear end of the double-ridge horn antenna by taking a z-axis as a center to form the double-ridge waveguide structure, a coaxial structure 5 is inserted into the tail end of the double-ridge waveguide along the y-axis, one coaxial end is higher than the double-ridge waveguide, for facilitating feeding, a probe 6 at the other end is connected with the ridge on the lower side of the double-ridge waveguide, and for ensuring the matching of the coaxial and double-ridge waveguides and reducing the return loss, a step matching structure 7 is added.
The spherical electromagnetic wave obtained by the coaxial-double-ridge waveguide conversion structure is converted into a non-uniform plane wave with an equiphase plane orthogonal to the propagation direction through a three-dimensional impedance matching lens fixed in a waveguide extension section of the horn antenna opening surface, and the non-uniform plane wave radiates to a free space. The lens antenna is easy to design, simple in structure and low in cost, and has wide working frequency band, high gain and low return loss through simulation verification.
The three-dimensional impedance matching lens antenna design principle is as follows, assuming that the thickness of the lens is t and the distance of the point source from the edge of the lens is f. Based on the geometric optics theory, the phase of the emitted wave is corrected through a three-dimensional impedance matching lens to form a non-uniform plane wave with an equiphase plane orthogonal to the propagation direction. According to the fermat's theorem, in order to ensure that the outgoing wave is a plane wave with an equal phase, it is necessary to ensure that the total optical path of any electromagnetic wave radiated from the point source is equal after passing through the free space and the lens. Therefore, assuming that the center of the lens is the origin of the coordinate axis, and the direction of the line from the point source to the center of the lens is the z direction, for any point (x, y, z) on the lens, there are:
wherein n is1Which is a free space refractive index, is typically taken to be 1,
Δ x, Δ y are the positional changes along the x-axis and y-axis, respectively, for the refractive index of the lens at (x, y, z).
Unlike other lenses, the equivalent refractive index of the three-dimensional impedance matching lens has a gradual change distribution in the three orthogonal directions x, y and z, which gradually decreases from the center to the two sides, and for convenience, it is assumed that the equivalent refractive index changes linearly in the three orthogonal directions, so equation (1) changes as follows:
order to
The above equation can be simplified as:
integrating the above equation, the equation becomes:
wherein n ism(z) is the maximum value of the refractive index of the lens in a direction further perpendicular to the z-axis, nm(z) is a function of the variable z only.
When z is fixed, the equation can be simplified as:
for convenience, assuming that the equivalent refractive index of the lens has the same linear variation trend in the x and y directions, there are:
assuming that the equivalent refractive index of the lens on both sides in the z direction should be 1, and the equivalent refractive index of the lens varies with decreasing linear center, therefore:
substituting the above equation into equation (5), then:
wherein n ism(0) Is the maximum value of the equivalent refractive index of the lens.
Assuming that the equivalent refractive index varies linearly, therefore:
nm(z)＝2n(x，y)-1 (9)；
therefore, according to equations (7), (8), and (9), the equivalent refractive index distribution of the entire lens can be obtained.
In this embodiment, the design steps of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens are described as follows:
1. double-ridge horn antenna, waveguide extension: in order to simplify the design of the three-dimensional impedance matching lens, the double-ridge horn antenna is a double-ridge pyramid horn antenna with a square opening surface, as shown in fig. 2, the extending part of the horn opening surface is a waveguide extension section, the waveguide extension section is a square frame, and the shape and the size of the waveguide opening surface are equal to those of the double-ridge horn antenna; the length of the waveguide extension section is equal to the thickness of the three-dimensional impedance matching lens, and the three-dimensional impedance matching lens is used for fixing the three-dimensional impedance matching lens on the mouth surface of the double-ridge horn antenna and completely covering the side edge of the three-dimensional impedance matching lens. Setting the center frequency of the double-ridged horn antenna to be 9.4GHz, and setting the diameter surface of the horn to be 195 multiplied by 195mm (6.11 wavelengths multiplied by 6.11 wavelengths) according to the formulas (7), (8) and (9); in order to ensure that the phase center of the horn is consistent with the focal length position of the lens, the focal length is set to be 299mm (9.37 wavelengths); to ensure that the waveguide extension completely covers the side of the three-dimensional impedance matching lens, the length of the waveguide extension is set to 30.396mm (0.95 wavelength). In order to expand the working frequency band of the horn antenna and facilitate feeding, a coaxial-double ridge waveguide conversion structure is adopted, as shown in fig. 3. In order to verify the performance of the double-ridged pyramid horn antenna, commercial full-wave simulation software CST is adopted for simulation verification, and the result shows that the-10 dB return loss bandwidth of the double-ridged pyramid horn antenna is 5.16-15.71GHz, and as shown in figure 4, the relative bandwidth is 101.1%, and the double-ridged pyramid horn antenna belongs to an ultra-wideband antenna.
2. Three-dimensional impedance matching lens: considering the square opening surface of the double-ridged pyramid horn antenna, the three-dimensional impedance matching lens is set to be in a rectangular parallelepiped shape. Based on the expressions (7), (8), and (9), the three-dimensional impedance matching lens was set to have a length and width of 195mm (6.11 wavelengths) and a thickness of 30.396mm (0.95 wavelength). The equivalent refractive index distribution of the three-dimensional matched lens in the form of a rectangular parallelepiped is shown in fig. 5, and the minimum equivalent refractive index of the lens is approximated to 1.2 in consideration that the equivalent refractive index of the equivalent refractive index unit cannot be completely equal to that of air. The three-dimensional impedance matching lens comprises a plurality of equivalent refractive index units, wherein the equivalent refractive index distribution of the lens is obtained according to the formulas (7), (8) and (9) so as to obtain an equivalent refractive index three-dimensional matrix, and the units with the same equivalent refractive index are correspondingly arranged according to the refractive index numerical values in the matrix, so that the three-dimensional impedance matching lens is finally obtained. The equivalent refractive index unit is composed of two types: one type comprises a pair of perforated medium substrates and a medium substrate with two sides covered by a square metal patch, wherein the pair of perforated medium substrates are symmetrically clung to two sides of the medium substrate with two sides covered by metal; one type of the medium base plate comprises three punching medium base plates, wherein the punching sizes of two punching medium base plates are fixed and equal, and the two punching medium base plates which are fixed and have equal sizes are symmetrically clung to two sides of the rest punching medium base plate.
The specific design steps of the equivalent refractive index unit in the invention are as follows:
(1) the discrete equivalent refractive index distribution of the three-dimensional matched lens was calculated and extracted by using Matlab software, and it was specified that the discrete interval in the x and y directions was 3mm (about 0.1 wavelength) and the discrete interval in the z direction was 2mm (about 0.06 wavelength), and a three-dimensional matrix of equivalent refractive index corresponding to the lens equivalent refractive index distribution was obtained.
(2) Considering that the three-dimensional matched lens has a discrete interval of 3mm (about 0.1 wavelength) in the x and y directions and a discrete interval of 2mm (about 0.06 wavelength) in the z direction, the equivalent refractive index unit size is set to 3mm (about 0.1 wavelength) in the x and y directions and 2mm (about 0.06 wavelength) in the z direction. The two equivalent refractive index units comprise a pair of perforated medium substrates 8 and a medium substrate 9 with two sides covered with square metal patches, the aperture radius of the perforated medium substrate 8 is fixed to be 1.25mm, the equivalent refractive index is adjusted by changing the side length A of the two square metal patches in the equivalent refractive index unit, the structural schematic diagram is shown in figure 6, and the range of the equivalent refractive index which can be covered by the equivalent refractive index units is 1.35-3.2 through simulation verification; one type of the medium substrate comprises three perforated medium substrates, wherein two perforated medium substrates 8 are fixed and equal in perforated size and have a radius of 1.25mm, the equivalent refractive index is adjusted by changing the size of the perforated radius R of the intermediate layer 10 of the equivalent refractive index unit, the structural schematic diagram of the medium substrate is shown in FIG. 7, and simulation verification shows that the equivalent refractive index range which can be covered by the medium substrate is 1.2-1.35. When two types of equivalent refractive index units are designed, the adopted dielectric substrate is a Teflon sheet material with the dielectric constant of 2.2 and the loss tangent of 0.0001, and the metal patch is made of pure copper.
(3) And correspondingly arranging equivalent refractive index units with different sizes according to the equivalent refractive index three-dimensional matrix to form the cuboid three-dimensional impedance matching lens. In order to simplify the processing difficulty, the three-dimensional impedance matching lens is processed in a layering mode through a PCB process, the three-dimensional impedance matching lens comprises 31 layers in total along the z axis, and no gap is reserved between the layers. The thicknesses of the 1 st layer dielectric substrate and the 31 th layer dielectric substrate are 0.5mm (0.016 wavelength), the thicknesses of the rest layers of dielectric substrates are 1mm (about 0.03 wavelength), the thickness of the metal patch is 0.018mm (0.00056 wavelength), and the total 31-layer structure is shown in fig. 8-15. The arrangement pattern of each layer is determined according to the lens design method, and when the variables in the formulas (7), (8), and (9) are given fixed values, the corresponding unique arrangement pattern is determined.
The double-ridge horn antenna is a broadband horn antenna, the working bandwidth of the lens antenna depends on the working bandwidth of the double-ridge horn antenna, and the double-ridge horn antenna can be replaced by other types of broadband horn antennas.
The shape of the three-dimensional impedance matching lens is the same as that of the opening surface of the double-ridge horn antenna, the value ranges of the lens on the x axis and the y axis are only limited during design, the value ranges are guaranteed to be equal to the size of the aperture of the antenna, and the value ranges of the x axis and the y axis are (-97.5mm, 97.5 mm).
In order to verify the performance of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens, commercial full-wave simulation software CST is adopted for simulation verification, and the verification result shows that:
(1) the-10 dB return loss bandwidth of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens is 5.25-15.2GHz, as shown in FIG. 16, the relative bandwidth is 97.3%, the ultra-wideband high-gain lens antenna belongs to an ultra-wideband antenna, and the advantages of wide frequency band and low return loss are verified;
(2) compared with a double-ridged pyramid horn antenna without the three-dimensional impedance matching lens, the gain of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens is improved in the full frequency band, the gain is improved by 1.2dB at the minimum, and the gain is improved by 15dB at the maximum, so that the advantages of high gain and high orientation are verified as shown in FIG. 17.
The invention is characterized in that a novel artificial electromagnetic medium is combined with a lens antenna, a lens with gradually-changed refractive index is constructed by using a sub-wavelength equivalent refractive index unit, the equivalent refractive index of the lens is gradually changed from the center to two sides in the three orthogonal directions of x, y and z, and particularly, in the electromagnetic wave propagation direction, the equivalent refractive index at two ends of the lens is 1 and is completely matched with a free space, and a matching layer is not required to be added or other technologies are not required to reduce the return loss of the antenna. The equivalent refractive index unit has a flat refractive index curve, so that the lens antenna can work in a very wide frequency band, and the working bandwidth of the lens antenna only depends on the bandwidth of the double-ridged horn antenna serving as a feed source. The lens antenna can keep high directivity and low return loss performance in the whole working frequency band, has the advantages of easy design, simple structure, low cost and the like, can replace the traditional uniform medium lens antenna, and has important application value in the fields of satellite communication, millimeter wave radar measurement, microwave biological imaging and the like.
Claims (6)
1. An ultra-wideband high-gain lens antenna based on a three-dimensional impedance matching lens is characterized in that: the three-dimensional impedance matching lens is embedded in the waveguide extension section, the length of the waveguide extension section is equal to the thickness of the three-dimensional impedance matching lens so as to completely cover the side edge of the three-dimensional impedance matching lens; the three-dimensional impedance matching lens comprises a plurality of equivalent refractive index units, wherein the equivalent refractive index units comprise two types, one type comprises a pair of perforated medium substrates and a medium substrate with two sides covered by a square metal patch, and the pair of perforated medium substrates are symmetrically clung to two sides of the medium substrate with two sides covered by metal; the other type of the device comprises three punching medium substrates, wherein the punching sizes of two punching medium substrates are fixed and equal, and the two punching medium substrates with the fixed and equal small holes are symmetrically and tightly attached to two sides of the rest punching medium substrate;
the equivalent refractive index subdivisions of the three-dimensional impedance matching lens are in gradient distribution in the x, y and z orthogonal directions, the gradient distribution is gradually decreased from the center to the two sides, along the propagation direction of electromagnetic waves, the equivalent refractive index of the two ends of the lens is 1, and the equivalent refractive index is completely matched with the free space.
2. The ultra-wideband high gain lens antenna based on the three-dimensional impedance matching lens as recited in claim 1, wherein: the three-dimensional impedance matching lens has a certain thickness, and the shape of the three-dimensional impedance matching lens is consistent with that of the opening surface of the horn antenna.
3. The ultra-wideband high gain lens antenna based on the three-dimensional impedance matching lens as recited in claim 1, wherein: the double-ridge horn antenna is a broadband horn antenna and used as a feed source to radiate broadband spherical waves, and the working bandwidth of the lens antenna depends on the working bandwidth of the double-ridge horn antenna.
4. A method for designing an ultra-wideband high-gain lens antenna based on a three-dimensional impedance matching lens as claimed in any one of claims 1-3, comprising the steps of:
(1) designing a double-ridge horn antenna and a waveguide extension section;
the double-ridge horn antenna is a double-ridge pyramid horn antenna with a square opening surface, the extending part of the horn opening surface is a waveguide extension section, the diameter surface of the horn opening is set according to a three-dimensional impedance matching lens design formula, and the length of the waveguide extension section is set for ensuring that the waveguide extension section completely covers the side edge of the three-dimensional impedance matching lens;
(2) designing a three-dimensional impedance matching lens;
considering a square opening surface of the double-ridged pyramid horn antenna, setting the three-dimensional impedance matching lens to be in a cuboid shape, and setting the length, the width and the thickness of the three-dimensional impedance matching lens according to a design formula of the three-dimensional impedance matching lens; the three-dimensional impedance matching lens comprises a plurality of equivalent refractive index units, wherein the equivalent refractive index units comprise two types: one type comprises a pair of perforated medium substrates and a medium substrate with two sides covered by a square metal patch, wherein the pair of perforated medium substrates are symmetrically clung to two sides of the medium substrate with two sides covered by metal; one type of the medium base plate comprises three punching medium base plates, wherein the punching sizes of two punching medium base plates are fixed and equal, and the two punching medium base plates which are fixed and have equal sizes are symmetrically clung to two sides of the rest punching medium base plate.
5. The design method of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens as claimed in claim 4, wherein the specific design steps of the equivalent refractive index unit are as follows:
(21) calculating and extracting discrete equivalent refractive index distribution of the three-dimensional matched lens by using Matlab software, wherein the discrete interval in the x direction and the y direction is about 0.1 wavelength, the discrete interval in the z direction is about 0.06 wavelength, and a three-dimensional matrix corresponding to the lens equivalent refractive index distribution is obtained, wherein the wavelength is specified as the central wavelength of the double-ridge horn antenna;
(22) considering that the discrete spacing of the three-dimensional matched lens in the x and y directions is about 0.1 wavelength, and the discrete spacing in the z direction is about 0.06 wavelength, the equivalent refractive index unit size is set to be about 0.1 wavelength in the x and y directions, and about 0.06 wavelength in the z direction; one type of the two equivalent refractive index units adjusts the equivalent refractive index by changing the side lengths of two layers of square metal patches in the equivalent refractive index units; the equivalent refractive index of the first type is adjusted by changing the size of the hole punched in the middle layer of the equivalent refractive index unit; when two types of equivalent refractive index units are designed, the adopted dielectric substrate is a Teflon sheet material with the dielectric constant of 2.2 and the loss tangent of 0.0001, and the metal patch is made of pure copper;
(23) and correspondingly arranging equivalent refractive index units with different sizes according to the equivalent refractive index three-dimensional matrix to form the cuboid three-dimensional impedance matching lens.
6. The design method of the ultra-wideband high-gain lens antenna based on the three-dimensional impedance matching lens as claimed in claim 4, wherein the calculation method of the equivalent refractive index distribution of the whole lens is as follows:
according to the Fermat's theorem, in order to ensure that the emergent wave is a plane wave with equal phase, it is necessary to ensure that the total optical path of any electromagnetic wave radiated from a point source is equal after passing through a free space and a lens; therefore, assuming that the center of the lens is the origin of the coordinate axis, and the direction of the line from the point source to the center of the lens is the z direction, for any point (x, y, z) on the lens, there are:
wherein n is1Is the free space refractive index; t is the thickness of the lens, and f is the vertical distance from the point source to the edge of the lens;
unlike other lenses, the equivalent refractive index of the three-dimensional impedance matching lens is gradually changed from the center to two sides in the three orthogonal directions x, y and z, and for convenience, the three-dimensional impedance matching lens is assumed to be linearly changed in the three orthogonal directions, so that the above formula is changed as follows:
order to
The above formula is simplified as follows:
integrating the above equation, the equation becomes:
when z is fixed, the above equation reduces to:
assuming that the equivalent refractive index of the lens has the same linear variation trend in the x and y directions, there are:
assuming that the equivalent refractive index of the lens on both sides in the z direction should be 1, and the equivalent refractive index of the lens varies with decreasing linear center, therefore:
substituting the above equation into equation (5), then:
wherein n ism(0) Is the maximum value of the equivalent refractive index of the lens;
assuming that the equivalent refractive index varies linearly, therefore:
nm(z)＝2n(x，y)-1 (9)；
therefore, according to equations (7), (8), and (9), the equivalent refractive index distribution of the entire lens is obtained.
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