阅读说明：本技术 一种基于反射式相位修正镜的准光单脉冲天线 (Quasi-optical monopulse antenna based on reflective phase correction mirror ) 是由 胡标 朱国锋 李�浩 汪海洋 李天明 周翼鸿 于 2021-08-23 设计创作，主要内容包括：本发明公开了一种基于反射式相位修正镜的准光单脉冲天线,属于太赫兹准光单脉冲天线领域。本发明采用两个低损耗反射式相位修正镜对和差比较器的辐射特性中存在的副瓣电平较高的问题进行改善,并提供了相位修正镜的镜面形状获取方法,极大的减少了现有技术采用介质透镜或衍射透镜带来的介质损耗的问题,最终同样可以较好地改善单脉冲天线的辐射特性。(The invention discloses a quasi-optical single-pulse antenna based on a reflective phase correcting mirror, and belongs to the field of terahertz quasi-optical single-pulse antennas. The invention adopts two low-loss reflection type phase correcting mirrors to improve the problem of higher sidelobe level in the radiation characteristic of the sum-difference comparator, and provides a method for obtaining the mirror surface shape of the phase correcting mirrors, thereby greatly reducing the problem of medium loss caused by adopting a medium lens or a diffraction lens in the prior art, and finally, also better improving the radiation characteristic of a single pulse antenna.)

1. A quasi-optical monopulse antenna based on a reflective phase correcting mirror is characterized by comprising a sum-difference comparator, a second phase correcting mirror and a first phase correcting mirror which are sequentially arranged along the axial direction;

the sum-difference comparator is an optical-alignment difference comparator and comprises a sum input port, an azimuth difference input port, a pitching difference input port and 4 output ports;

the first phase correcting mirror is a curved surface reflecting mirror with a round hole output port at the center, and is used for reflecting and converging 4 wave beams output by the sum-difference comparator to the second phase correcting mirror, and correcting and optimizing the phases of the 4 wave beams so that the phases of the 4 wave beams reaching the second phase correcting mirror meet the sum-difference effect;

the second phase correcting mirror is a curved surface reflecting mirror and is used for reflecting 4 wave beams to the round hole output port of the first phase correcting mirror to be synthesized and output, and simultaneously, the phases of the 4 wave beams are corrected for the second time so that the phases reaching the round hole output port meet the sum-difference effect.

2. The quasi-optical monopulse antenna based on the reflective phase correcting mirror as claimed in claim 1, wherein the mirror surface shapes of the first phase correcting mirror and the second phase correcting mirror are obtained by:

s1: determining an initial field of a phase correcting mirrorAnd a target field

Defining the incident field of the initial surface S of the phase correcting mirror as the initial fieldObject fieldFor observing plane S₀A desired field distribution; wherein the content of the first and second substances,is the position vector of the initial plane S,for observing plane S₀A position vector of (a);

for the first phase correction mirror: initial field of the first phase correcting mirrorA field for the output field of the preceding stage sum-difference comparator to reach the initial plane S of the first phase correction mirror;

output field distribution and observation plane S according to known preceding stage sum-difference comparator₀Determining the shape and position of the initial surface S of the first phase correction mirror according to the expected target field distribution to reflect and converge 4 wave beams output by the preceding stage sum-difference comparator to the observation plane S₀；

For the second phase correction mirror: the second phaseInitial field of the position correcting mirrorThe observation field corrected by the first phase correcting mirror; the plane where the second phase correction mirror is located is an observation plane S of the first phase correction mirror₀(ii) a An observation plane S of the second phase correction mirror₀The plane of the circular hole output port is;

s2: calculating the initial field from equation (1)Reflected field after reflection from the initial surface S

WhereinIs the mirror disturbance of the phase correcting mirror, k is the propagation constant, and gamma is the initial fieldThe included angle between the incident direction and the normal direction of the mirror surface;

s3: calculating the reflected field from a scalar diffraction integral equationTo the observation plane S₀Observation field distribution of

Wherein G is a Green function of free space, and the expression is as follows:

s4: defining observation field distributionsAnd the target fieldThe difference amounts of (A) and (B) are as follows:

s5: carrying out rectangular grid discretization on the initial surface S, wherein the side length of the grid in the x direction is delta x, the number of the grids is V, the side length of the grid in the y direction is delta y, and the number of the grids is W; thus position vectorWritten in the form of three coordinates:wherein v is the grid serial number in the x direction, and w is the grid serial number in the y direction; so that the mirror surface disturbance amount of the phase correcting mirrorWrite as:whereinRepresenting the specular disturbance vector, delta representing the Dirac function, a_vwRepresentative pointThe amplitude of the disturbance at (a) is,a position vector representing the v-th grid in the x direction and the w-th grid in the y direction;

s6: will observe the plane S₀Discretizing a rectangular grid at x₀Length of grid side in direction of Deltax₀The number of grids is V, at y₀Length of grid side in direction of Deltay₀The number of grids W; thus position vectorWritten in the form of three coordinates:wherein v is x₀Grid number of direction, w is y₀Grid number of direction;

discretizing the formula (3):

whereinIs a discretized observation field distribution;

s7: calculating a target fieldAnd observation fieldThe minimum value of the difference value, and the extreme point of the continuous function can be represented by zero of the first derivative according to the property of the function, so thatObtaining an iterative formula (5):

whereink₀For the free space wave number, the prime symbol "represents taking the complex conjugate, and i is the number of iterations; obtaining the disturbance quantity of any point on the mirror surface of the phase correcting mirror through repeated iteration of a formula (5), thereby obtaining the optimized mirror surface shape of the phase correcting mirror;

s8: according to the radius of the final output beam, a round hole output port is arranged at the center of the first phase correction mirror obtained in the step S7; and intercepting the circular mirror surface structure as the second phase correction mirror by taking the center of the second phase correction mirror obtained in the step S7 as the center of a circle, so that the second phase correction mirror meets the requirements of not shielding the output beam of the preceding stage sum-difference comparator and also realizing the phase correction of the beam.

3. The quasi-optical monopulse antenna based on a reflective phase correcting mirror as claimed in claim 2, wherein the shape of the initial surface S of the first phase correcting mirror is formed by splicing four rectangular plane mirrors with the same size.

4. The quasi-optical monopulse antenna based on a reflective phase correcting mirror as claimed in claim 2, wherein the initial surface S of the second phase correcting mirror is a rectangular plane mirror.

Technical Field

The invention belongs to the field of terahertz quasi-optical single-pulse antennas, and particularly relates to a quasi-optical single-pulse antenna based on a reflective phase correction mirror.

Background

As a precise angle measurement technology, the monopulse technology can determine the position information of a target theoretically only by analyzing one echo pulse, and the speed of extracting the position information of the target is greatly increased. For the quasi-optical single pulse antenna of the terahertz frequency band, the sum beam directly radiated from the end face of the quasi-optical sum-difference comparator has the problem of higher side lobe level, because the distance of the beam radiated from the port of the quasi-optical sum-difference comparator is large relative to the wavelength, and therefore, in order to obtain better sum-difference radiation characteristics, the side lobe level must be suppressed by improving the field distribution of the output port surface. At present, the purpose of improving the output end surface field of the sum and difference comparator can be achieved by using some optical elements such as dielectric lens antenna, diffraction lens and the like, so as to obtain the expected directional diagram. Although these optical elements have advantages such as simple structure, small size, and low processing cost, they have a problem of large loss due to dielectric loss, and it is important to find a technical solution with low loss, high efficiency, and easy processing.

Disclosure of Invention

The quasi-optical monopulse antenna based on the reflective phase correcting mirror can improve the field distribution of the output port of the quasi-optical sum-difference comparator and optimize the radiation characteristic, and has the advantages of low loss, high efficiency and easiness in processing.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a quasi-optical single pulse antenna based on a reflection type phase correcting mirror comprises a sum-difference comparator, a second phase correcting mirror and a first phase correcting mirror which are sequentially arranged along the axial direction.

The sum-difference comparator is an optical-alignment difference comparator and comprises a sum input port, an azimuth difference input port, a pitching difference input port and 4 output ports; when a Gaussian beam enters from the input port, 4 beams output by 4 output ports have the same amplitude and the same phase; when a Gaussian beam enters from the pitching difference input port, the amplitudes of 4 beams output by 4 output ports are the same, and the phase difference between the upper two beams and the lower two beams is 180 degrees; when a Gaussian beam enters from the azimuth difference input port, the amplitudes of 4 beams output by the 4 output ports are the same, and the phase difference between the two beams on the left side and the two beams on the right side is 180 degrees.

The first phase correcting mirror is a curved surface reflecting mirror with a round hole output port at the center, and is used for reflecting and converging 4 wave beams output by the sum-difference comparator to the second phase correcting mirror, and correcting and optimizing the phases of the 4 wave beams so that the phases of the 4 wave beams reaching the second phase correcting mirror meet the sum-difference effect.

The second phase correcting mirror is a curved surface reflecting mirror and is used for reflecting 4 wave beams to the round hole output port of the first phase correcting mirror to be synthesized and output, and simultaneously, the phases of the 4 wave beams are corrected for the second time so that the phases reaching the round hole output port meet the sum-difference effect.

Further, the mirror surface shapes of the first phase correction mirror and the second phase correction mirror are obtained by the following steps:

s1: determining an initial field of a phase correcting mirrorAnd a target field

Defining the incident field of the phase correcting mirror as the initial fieldObject fieldFor observing plane S₀The desired field distribution. Wherein the content of the first and second substances,is the position vector of the initial plane S,for observing plane S₀The position vector of (2).

For the first phase correction mirror: initial field of the first phase correcting mirrorThe field reaching the initial plane S of the first phase correction mirror is the output field of the preceding stage sum-difference comparator.

Output field distribution and observation plane S according to known preceding stage sum-difference comparator₀Determining the shape and position of the initial surface S of the first phase correction mirror according to the expected target field distribution to reflect and converge 4 wave beams output by the preceding stage sum-difference comparator to the observation plane S₀。

Further, the shape of the initial surface S is formed by splicing four rectangular plane mirrors with the same size.

For the second phase correction mirror: initial field of the second phase correction mirrorThe observation field corrected by the first phase correcting mirror; the plane where the second phase correction mirror is located is an observation plane S of the first phase correction mirror₀(ii) a An observation plane S of the second phase correction mirror₀Is the plane of the circular hole output port.

Further, the initial surface S of the second phase correction mirror is a rectangular plane mirror. S2: calculating the initial field from equation (1)Reflected field after reflection from the initial surface S

WhereinIs a phase correcting mirrorK is a propagation constant and gamma is an initial fieldThe incident direction and the normal angle of the mirror surface.

S3: calculating the reflected field from a scalar diffraction integral equationTo the observation plane S₀Observation field distribution of

Wherein G is a Green function of free space, and the expression is as follows:

s4: defining observation field distributionsAnd the target fieldThe difference amounts of (A) and (B) are as follows:

s5: carrying out rectangular grid discretization on the initial surface S, wherein the side length of the grid in the x direction is delta x, the number of the grids is V, the side length of the grid in the y direction is delta y, and the number of the grids is W; thus position vectorWritten in the form of three coordinates:wherein v is the grid serial number in the x direction, and w is the grid serial number in the y direction; so that the mirror surface disturbance amount of the phase correcting mirrorWrite as:whereinRepresenting the specular disturbance vector, delta representing the Dirac function, a_vwRepresentative pointThe amplitude of the disturbance at (a) is,the position vector of the v-th grid in the x direction and the w-th grid in the y direction is shown.

S6: will observe the plane S₀Discretizing a rectangular grid at x₀Length of grid side in direction of Deltax₀The number of grids is V, at y₀Length of grid side in direction of Deltay₀The number of grids W; thus position vectorWritten in the form of three coordinates:wherein v is x₀Grid number of direction, w is y₀Grid number of direction.

Discretizing the formula (3):

whereinIs a discretized field distribution of view.

S7: calculating a target fieldAnd observation fieldFinding the minimum value of the difference, i.e. finding the extreme value of the difference, and according to the property of the continuous function, the extreme point of the function can be represented by the first derivative being zero, so thatObtaining an iterative formula (5):

whereink₀For the free space wavenumber, the superscript ". sup." represents taking the complex conjugate, and i is the number of iterations. The disturbance amount at any point on the mirror surface of the phase correction mirror is obtained through repeated iteration of the formula (5), so that the optimized phase correction mirror surface shape is obtained.

S8: according to the radius of the final output beam, a round hole output port is arranged at the center of the first phase correction mirror obtained in the step S7; and intercepting the circular mirror surface structure as the second phase correction mirror by taking the center of the second phase correction mirror obtained in the step S7 as the center of a circle, so that the second phase correction mirror meets the requirements of not shielding the output beam of the preceding stage sum-difference comparator and also realizing the phase correction of the beam.

In practical application, the central distance between the four beams radiated by the output ports of the quasi-optical and differential comparators is large relative to the wavelength, and the radius of the emergent beam of the sum and differential comparator is large, so that the output field distribution of the quasi-optical and differential comparators has a certain deviation compared with an ideal output field. Therefore, the invention obtains the mirror surface shape of the first phase correction mirror by setting the target field, thereby realizing the reduction of the beam radius and the phase correction, and ensuring that the energy leakage is little and the phase requirement is basically met when the beam reaches the second phase correction mirror; the second phase correction mirror is mainly used for changing the radiation direction of the wave beams, and simultaneously further performing phase correction on the four wave beams, so that the final target field is guaranteed to be achieved at the output port of the circular hole. Compared with the mainstream method adopting a dielectric lens or a diffraction lens, the method adopts a reflection mode in the transmission process, and has the advantages of low transmission loss and high transmission efficiency.

Drawings

Fig. 1 is a schematic diagram of a phase correction mirror.

FIG. 2 is a schematic structural diagram of radiation characteristics of a terahertz quasi-optical single-pulse antenna based on a phase correction mirror.

Fig. 3 is a sum-difference pattern on the initial azimuth plane.

Fig. 4 is a sum and difference pattern on the initial pitch plane.

Fig. 5 is a sum-difference pattern on the corrected azimuth plane.

Fig. 6 is a sum-difference pattern on the corrected pitch plane.

The reference numbers illustrate: 1 quasi-optical sum-difference comparator, 2 second phase correcting mirror, 3 first phase correcting mirror.

Detailed Description

The following describes embodiments of the present invention with reference to the drawings.

Fig. 2 is a schematic structural diagram of the present embodiment, and as shown in fig. 2, the structure includes: the device comprises a quasi-light sum-difference comparator, a second phase correcting mirror and a first phase correcting mirror which are sequentially arranged along the axial direction.

The first phase correcting mirror is a curved surface reflecting mirror with a round hole output port at the center, and is used for reflecting and converging 4 wave beams output by the sum-difference comparator to the second phase correcting mirror, and correcting and optimizing the phases of the 4 wave beams so that the phases of the 4 wave beams reaching the second phase correcting mirror meet the sum-difference effect.

The second phase correcting mirror is a curved surface reflecting mirror and is used for reflecting 4 wave beams to the round hole output port of the first phase correcting mirror to be synthesized and output, and simultaneously, the phases of the 4 wave beams are corrected for the second time so that the phases reaching the round hole output port meet the sum and difference effect.

The working frequency of the Gaussian beam provided by the front stage quasi-optical sum-difference comparator is 340GHz, and the field distribution provided by the front stage quasi-optical sum-difference comparator is sum beam field distribution, azimuth difference beam field distribution and elevation difference beam field distribution respectively. The neutral beam field distribution is represented by four Gaussian beams with equal amplitude and same direction, the azimuth difference beam field distribution is represented by the fact that the amplitudes of the left two beams are equal to the amplitudes of the right two beams, but the phase difference is 180 degrees, and the elevation difference beam field distribution is represented by the fact that the amplitudes of the upper two beams are equal to the amplitudes of the lower two beams, but the phase difference is 180 degrees.

The method for calculating the mirror surface shape of the first phase correction mirror comprises the following steps: the output field at the output port of the known standard optical sum and difference comparator has a beam radius of about 9.4mm, a distance of 50mm between the centers of the four beams, and center coordinates of (25, 25, 0), (25, -25, 0), (-25, 25, 0), in mm. Fig. 3 and 4 are far field patterns of the azimuth and elevation planes of the quasi-optic sum-difference comparator.

The target field expected by the first phase correction mirror is a Gaussian beam with the beam waist radius of 6mm, so that the initial surface S of the first phase correction mirror is set to be composed of 4 rectangular plane mirrors with 50mm x 50mm, the central coordinates of the plane mirrors are (0, 0, 102), and the unit mm is adopted, so that the 4 beams output by the sum-difference comparator are reflected and converged to an observation plane.

According to the steps recorded in the invention content, the structure of the first phase correction mirror can be calculated through an iterative formula, and the reflection convergence of four paths of wave beams and the phase correction are completed; and then according to the final radius of the output beam, digging a round through hole with the radius of 18mm at the center of the first phase correcting mirror, and ensuring that the corrected beam can radiate sum and difference beams through the round hole.

The mirror surface shape of the second phase correction mirror is calculated similarly: and taking the observation field corrected by the first phase correction mirror as an initial field of a second phase correction mirror, setting a target field of the second phase correction mirror as a Gaussian beam with the beam waist radius of 4mm, setting an initial surface S of the second phase correction mirror as a rectangular plane structure with the beam waist radius of 20mm x 20mm, and setting the central coordinate of the rectangular plane structure as (0, 0, 0) and the unit mm. Finally, in order to prevent the second phase correction mirror from blocking the incident beam, a rectangular structure of 20mm x 20mm is cut into a circular structure with a radius of 20 mm.

In order to verify the accuracy of the result, the obtained phase correction mirror is led into simulation software, and a whole simulation model is built in the simulation software. Fig. 5 shows the sum and difference far-field pattern in the azimuth difference direction, and fig. 6 shows the sum and difference far-field pattern in the elevation difference direction, and it can be seen from the figure that the sum beam side lobe is below-15 dB on average. From the transmission efficiency, the transmission efficiency of the invention is about 85%, and the loss is low.

The result shows that the quasi-optical monopulse antenna based on the reflective phase correcting mirror has the advantages of low loss, high efficiency and easiness in processing. A new method is provided for improving the output port field of the quasi-optical sum-difference comparator and optimizing the radiation characteristic of the quasi-optical sum-difference comparator.