阅读说明：本技术 一种基于量子级联的rcs测量收发系统 (RCS measurement transceiving system based on quantum cascade ) 是由 都妍 贾洁姝 霍熠炜 李永晨 陈亚南 武亚君 于 2021-08-03 设计创作，主要内容包括：一种基于量子级联的RCS测量收发系统,用于测量待测目标的雷达散射截面,包括光源、本振光路、信号光路和检测组件；所述本振光路包括本振参考光路和本振测量光路；所述信号光路包括信号参考光路和信号测量光路；所述信号测量光路包含紧缩场,所述待测目标设置在紧缩场中；由光源发射的光信号通过上述光路可分别得到本振参考光、本振测量光、信号参考光和信号测量光,并分别馈入检测组件；所述检测组件对接收到的本振参考光、信号参考光进行混频,对接收到的本振测量光、信号测量光进行混频,并对混频后的信号进行分析得到待测目标的RCS信息。本发明可实现待测目标RCS的高灵敏度测量,具有体积小、光路结构简单、静区尺寸大的优点。(An RCS measurement transceiving system based on quantum cascade is used for measuring a radar scattering cross section of a target to be measured and comprises a light source, a local oscillator light path, a signal light path and a detection component; the local oscillator optical path comprises a local oscillator reference optical path and a local oscillator measurement optical path; the signal light path comprises a signal reference light path and a signal measuring light path; the signal measurement optical path comprises a compact range, and the target to be measured is arranged in the compact range; the optical signal emitted by the light source can respectively obtain local oscillator reference light, local oscillator measurement light, signal reference light and signal measurement light through the optical path, and the local oscillator reference light, the local oscillator measurement light, the signal reference light and the signal measurement light are respectively fed into the detection component; the detection component carries out frequency mixing on the received local oscillator reference light and the received signal reference light, carries out frequency mixing on the received local oscillator measuring light and the received signal measuring light, and carries out analysis on the signals after frequency mixing to obtain RCS information of the target to be detected. The invention can realize the high-sensitivity measurement of the RCS of the target to be measured and has the advantages of small volume, simple light path structure and large size of a dead zone.)

1. An RCS measurement transceiving system based on quantum cascade is used for measuring a radar scattering cross section of a target to be measured, and is characterized by comprising a light source (A1), a local oscillator light path, a signal light path and a detection component;

the local oscillator optical path comprises a local oscillator reference optical path and a local oscillator measurement optical path;

the signal light path comprises a signal reference light path and a signal measuring light path; the signal measurement optical path comprises a compact range, and the target to be measured is arranged in the compact range;

transmitting an optical signal emitted by a light source through a local oscillator reference optical path to obtain local oscillator reference light, and feeding the local oscillator reference light into a detection component; transmitting an optical signal emitted by a light source through a local oscillator measurement optical path to obtain local oscillator measurement light, and feeding the local oscillator measurement light into a detection component;

transmitting an optical signal emitted by the light source through a signal reference light path to obtain signal reference light, and feeding the signal reference light into the detection component; transmitting an optical signal emitted by a light source through a signal measurement light path to obtain signal measurement light of a target to be measured, and feeding the signal measurement light into a detection component;

the detection component carries out frequency mixing on the received local oscillator reference light and the received signal reference light, carries out frequency mixing on the received local oscillator measuring light and the received signal measuring light, and carries out analysis on the signals after frequency mixing to obtain RCS information of the target to be detected.

2. The quantum cascade-based RCS measurement transceiver system of claim 1, wherein the compact comprises an transmit compact and a receive compact.

3. The RCS measurement transceiving system based on quantum cascade of claim 1, wherein the local oscillator reference optical path comprises a beam shaping mirror (R8), a fifth light splitting film (S5), a sixth plane mirror (R9), a third light splitting film (S3), a seventh plane mirror (R10), a second light splitting film (S2) and a second lens (L2) which are arranged in sequence;

an optical signal emitted by a light source (A1) is firstly subjected to beam shaping through a beam shaping mirror (R8) to form a collimated light beam, then the collimated light beam is subjected to beam splitting through a fifth light splitting film (S5), transmitted light after the beam splitting of the fifth light splitting film (S5) reaches a third light splitting film (S3) after being reflected by a sixth plane mirror (R9), and the transmitted light beam after the beam splitting of the third light splitting film (S3) is sequentially subjected to reflection of a seventh plane mirror (R10) and the second light splitting film (S2), is focused through a second lens (L2), and is fed into the detection assembly as local oscillator reference light.

4. The RCS measurement transceiving system based on quantum cascade of claim 1, wherein the local oscillator measurement optical path comprises a beam shaping mirror (R8), a fifth light splitting film (S5), a sixth plane mirror (R9), a third light splitting film (S3), a fourth light splitting film (S4) and a first lens (L1) which are arranged in sequence; an optical signal emitted by a light source (A1) is firstly subjected to beam shaping through a beam shaping mirror (R8) to form a collimated light beam, then the collimated light beam is subjected to beam splitting through a fifth light splitting film (S5), transmitted light subjected to beam splitting through the fifth light splitting film (S5) is reflected through a sixth plane mirror (R9) and reaches a third light splitting film (S3), a reflected light beam subjected to beam splitting through the third light splitting film (S3) is reflected through a fourth light splitting film (S4), and the reflected light beam is focused through a first lens (L1) and is fed into the detection assembly as local oscillation measuring light.

5. The quantum cascade-based RCS measurement transceiver system as claimed in claim 1, wherein the signal reference optical path comprises a beam shaping mirror (R8), a fifth light splitting film (S5), a first plane mirror (R1), a second plane mirror (R2), a first light splitting film (S1), a second light splitting film (S2) and a second lens (L2) which are arranged in sequence;

an optical signal emitted by a light source (A1) is firstly subjected to beam shaping through a beam shaping mirror (R8) to form a collimated light beam, then the collimated light beam is split through a fifth light splitting film (S5), a reflected light beam split by the fifth light splitting film (S5) is reflected through a first plane mirror (R1) and a second plane mirror (R2) in sequence and reaches a first light splitting film (S1), and a transmitted light beam split through the first light splitting film (S1) is transmitted through a second light splitting film (S2) in sequence and focused through a second lens (L2) and then serves as signal reference light to be fed into a detection assembly.

6. The RCS measurement transceiving system based on quantum cascade of claim 1, wherein the signal measurement optical path comprises a beam shaping mirror (R8), a fifth light splitting film (S5), a first plane mirror (R1), a second plane mirror (R2), a first light splitting film (S1), a compact field, a fourth light splitting film (S4) and a first lens (L1) which are arranged in sequence;

an optical signal emitted by a light source (A1) is firstly subjected to beam shaping through a beam shaping mirror (R8) to form a collimated light beam, then the collimated light beam is subjected to beam splitting through a fifth light splitting film (S5), a reflected light beam subjected to beam splitting through the fifth light splitting film (S5) is reflected through a first plane mirror (R1) and a second plane mirror (R2) in sequence and reaches a first light splitting film (S1), the reflected light beam subjected to beam splitting through the first light splitting film (S1) enters a compact range as an emission signal, the optical signal subjected to beam expansion through the emission compact range fully irradiates a target, a received signal reflected by the target further passes through the reception compact range and reaches a fourth light splitting film (S4), and the light signal transmitted by the fourth light splitting film (S4) is focused through a first lens (L1) and is fed into a detection assembly as signal measuring light.

7. The RCS measurement transceiving system based on quantum cascade of claim 6, wherein the emission compact band comprises a secondary emission mirror (R3), a fourth plane mirror (R4), a fifth plane mirror (R5) and a main reflecting plane (R6) which are arranged in sequence;

the reflected light after being split by the first light splitting film (S1) is used as an emission signal to reach an emission secondary mirror (R3), and after being reflected by the emission secondary mirror (R3), a fourth plane mirror (R4) and a fifth plane mirror (R5) in sequence, the reflected light reaches a main reflecting surface (R6), and after being reflected by the main reflecting surface (R6), the radius of the light beam is enlarged, so that parallel light beams are formed to irradiate the target to be measured.

8. The quantum cascade-based RCS measurement transceiver system according to claim 7, wherein said receiving compact field comprises a main reflecting surface (R6), a fifth plane mirror (R5) and a receiving sub mirror (R7) arranged in sequence;

the optical signal reflected by the target to be measured reaches the main reflecting surface (R6), is reflected by the main reflecting surface (R6) and the fifth plane mirror (R5) in sequence and then reaches the receiving auxiliary mirror (R7), and after being reflected by the receiving auxiliary mirror (R7), parallel light beams are formed and reach the fourth light dividing film (S4), and the radius of the parallel light beams is reduced to the size before beam expansion.

9. A quantum cascade-based RCS measurement transceiver system according to claim 1, characterized in that the detection component comprises a test mixer (M1), a reference mixer (M2) and a vector network analyzer (B1); the test mixer (M1) mixes the fed local oscillator measurement light and the signal measurement light to obtain a test intermediate frequency signal, and the reference mixer (M2) mixes the fed local oscillator reference light and the signal reference light to obtain a reference intermediate frequency signal;

and the test intermediate frequency signal and the reference intermediate frequency signal are respectively input into a vector network analyzer (B1), and the vector network analyzer analyzes to obtain RCS information of the target to be tested.

10. The RCS measurement transceiving system based on quantum cascade of claim 8, wherein the main reflecting surface (R6), the transmitting sub-mirror (R3) and the receiving sub-mirror (R7) are off-axis parabolic mirrors with the same off-axis angle, and the transmitting sub-mirror (R3) and the receiving sub-mirror (R7) have the same caliber and focal length, and the calibers are in the range of 100mm to 150 mm.

Technical Field

The invention relates to a quantum cascade RCS measurement transmitting and receiving system, and belongs to the technical field of terahertz radar cross section measurement.

Background

The terahertz waves (0.1-10 THz, corresponding to the wavelength of 30 mu m-3 mm) are extremely short in wavelength, have stronger target scattering characteristic depiction capacity and can present electromagnetic scattering characteristics different from the frequency bands of microwave and infrared visible light. In recent years, the research on the scattering characteristics and mechanism of terahertz waves by an object is more and more emphasized, and the related technology of terahertz radar is more important. An important branch of terahertz radar systems is the Radar Cross Section (RCS) for measuring objects, which has the advantages: firstly, the terahertz wavelength is shorter than the common radar wave band, and the application of the terahertz wavelength in the scaling RCS detection can make the scaling ratio larger, so that the terahertz wavelength is particularly suitable for large-scale target detection; secondly, the terahertz wave radar has higher transverse resolution than the microwave radar theoretically, the absolute bandwidth of terahertz signals is also larger, and the target imaging identification capability is far higher than that of the common microwave radar; thirdly, at present, no invisible airplane designed for terahertz wave bands exists, and an effective invisible effect on terahertz wave band detection systems is difficult to achieve.

At present, methods for realizing a terahertz target RCS coherent measurement system mainly include a femtosecond laser-based terahertz time-domain spectroscopy measurement system, an infrared laser-based scattering measurement system, and a quantum cascade laser-based measurement system. The differences between these systems are mainly in frequency range, quiet zone size and data information.

Currently, terahertz RCS measurement systems can be divided into two categories, electronics and optics, according to different implementations of terahertz sources. The system realized by an electronics mode mainly refers to a measuring system for generating terahertz waves based on a solid-state microwave frequency doubling mode, and the system realized by an optical mode mainly comprises a terahertz time-domain spectroscopy (TDS) measuring system based on a femtosecond laser, a scattering measuring system based on a far infrared laser and a terahertz RCS measuring system based on a quantum cascade laser. The microwave up-conversion is realized based on a solid-state frequency doubling circuit, the frequency band is mainly below 1THz, the technology is relatively mature, but the frequency band above 1THz is difficult to break through; the terahertz time-domain spectroscopy RCS testing technology can realize THz wave detection in a wide frequency spectrum range, the frequency band is mainly 0.1-2 THz, the system is low in emission power and small in quiet zone size, and the obtained RCS data generally does not contain phase information; the RCS test system based on the far infrared laser has the test frequency of more than 1THz, the main working mode is spot frequency and small bandwidth sweep frequency measurement, the current mature realization test frequency band is 1.56THz, and the system has large volume, complex structure and small size of dead space; the test frequency of the RCS test system based on the terahertz quantum cascade laser can reach more than 2THz, the emission power of the terahertz quantum cascade laser is relatively high, large dead zone test is potentially realized, but the target RCS test system based on a single QCL is not reported yet at present.

Patent CN102435987A discloses an RCS measuring device based on a single continuous laser, the device is a double-station imaging transmit-receive system, and the adopted terahertz laser is CO₂The laser is large in size and not beneficial to system integration, an included angle between an incident beam and a scattered beam of a target to be measured is smaller than 5 degrees, power transmission efficiency is low, full utilization of terahertz emission power is not facilitated, the size of a quiet area of the system is small, and full irradiation measurement of the target cannot be achieved. Patent 103134983a discloses a terahertz coherent detection system and method based on a single mixer, the method needs two lasers as a signal source and a reference source, wherein the signal source is a 2.7THz quantum cascade laser, the reference source is the third harmonic output of a 900GHz band solid-state semiconductor laser, and the circuit is complex. Prospectra for quaternary calcium phosphate lasers as transmitters and local emulsifiers in, Jerry Waldman et al, Laurel university, Massachusetts, USAThe coherent terahertz transmitter/receiver systems, proc.of SPIE,2009(7215) proposes a concept of building a single-station terahertz target RCS measurement system by using two quantum cascade lasers as a signal source and a reference source respectively, but the system only stays at the design stage. A small double-station-angle target RCS Coherent measurement system is constructed by a Coherent imaging at 2.4THz with a CW quantum cascade laser transmitter, Proc.of SPIE,2010(7601) published by Andrio school A.Danylov et al of Massachusetts university, and comprises two terahertz lasers, wherein a signal source is 2.408THz quantum cascade laser, and a reference source is 2.409THz far infrared gas laser, so that the system is expensive in cost and large in volume.

Disclosure of Invention

The invention provides a quantum cascade-based RCS measurement transceiving system which is used for measuring a radar scattering cross section of a target to be measured, and solves the technical problems that a terahertz waveband RCS measurement system is low in transmission efficiency, high in cost, small in size of a dead zone and incapable of obtaining RCS phase information.

In order to solve the above problems, one technical solution of the present invention is as follows: an RCS measurement transceiving system based on quantum cascade is used for measuring a radar scattering cross section of a target to be measured and comprises a light source, a local oscillator light path, a signal light path and a detection component; the local oscillator optical path comprises a local oscillator reference optical path and a local oscillator measurement optical path; the signal light path comprises a signal reference light path and a signal measuring light path; the signal measurement optical path comprises a compact range, and the target to be measured is arranged in the compact range; transmitting an optical signal emitted by a light source through a local oscillator reference optical path to obtain local oscillator reference light, and feeding the local oscillator reference light into a detection component; transmitting an optical signal emitted by a light source through a local oscillator measurement optical path to obtain local oscillator measurement light, and feeding the local oscillator measurement light into a detection component; transmitting an optical signal emitted by the light source through a signal reference light path to obtain signal reference light, and feeding the signal reference light into the detection component; transmitting an optical signal emitted by a light source through a signal measurement light path to obtain signal measurement light of a target to be measured, and feeding the signal measurement light into a detection component; the detection component carries out frequency mixing on the received local oscillator reference light and the received signal reference light, carries out frequency mixing on the received local oscillator measuring light and the received signal measuring light, and carries out analysis on the signals after frequency mixing to obtain RCS information of the target to be detected.

Preferably, the compact range comprises an emitting compact range and a receiving compact range.

The local oscillation reference light path comprises a beam shaping mirror, a fifth light splitting film, a sixth plane mirror, a third light splitting film, a seventh plane mirror, a second light splitting film and a second lens which are sequentially arranged; the light signal by the light source outgoing carries out beam shaping through the beam shaping mirror at first, forms collimated light beam, then through fifth beam splitting membrane beam splitting, and the transmission light after fifth beam splitting membrane beam splitting reaches third beam splitting membrane after the reflection of sixth plane mirror, and the transmission light beam after third beam splitting membrane passes through the reflection of seventh level mirror and second beam splitting membrane in proper order, through the focus of second lens, as local oscillator reference light feed in detection component.

The local oscillation measuring light path comprises a beam shaping mirror, a fifth light splitting film, a sixth plane mirror, a third light splitting film, a fourth light splitting film and a first lens which are arranged in sequence; the light signal by the light source outgoing carries out beam shaping through beam shaping mirror at first, forms collimated light beam, then through fifth beam splitting membrane beam splitting, and the transmission light after fifth beam splitting membrane beam splitting reaches third beam splitting membrane after sixth plane mirror reflection, and the reflected light beam after third beam splitting membrane passes through fourth beam splitting membrane reflection, and through the focus of first lens, as the local oscillator measuring light feed in detection component.

The signal reference light path comprises a beam shaping mirror, a fifth light splitting film, a first plane mirror, a second plane mirror, a first light splitting film, a second light splitting film and a second lens which are sequentially arranged; the light signal by the light source outgoing carries out beam shaping through the beam shaping mirror at first, forms collimated light beam, then through fifth beam splitting membrane beam splitting, the reflected beam after fifth beam splitting membrane beam splitting reaches first beam splitting membrane after the reflection of first plane mirror and second plane mirror in proper order, and the transmission light beam after first beam splitting membrane beam splitting passes through second beam splitting membrane transmission and second lens focus in proper order after, as signal reference light feed-in detection component.

The signal measuring light path comprises a beam shaping mirror, a fifth light splitting film, a first plane mirror, a second plane mirror, a first light splitting film, a compact range, a fourth light splitting film and a first lens which are sequentially arranged; the light signal by light source outgoing carries out beam shaping through beam shaping mirror at first, form collimated light beam, then through fifth beam splitting membrane beam splitting, the reflected beam after fifth beam splitting membrane beam splitting passes through the reflection of first plane mirror and second plane mirror in proper order after, reach first beam splitting membrane, the reflected beam of first beam splitting membrane beam splitting gets into the compact range as emission signal, the target is irradiated entirely to the light signal after expanding the beam through the emission compact range, received signal by the target reflection further passes through the receipt compact range, reach fourth beam splitting membrane, the transmission light of fourth beam splitting membrane passes through the focus of first lens, as signal measurement light feed-in detection component.

The emission compact range comprises an emission secondary mirror, a fourth plane mirror, a fifth plane mirror and a main reflecting surface which are sequentially arranged; the reflected light split by the first light splitting film is used as a transmitting signal to reach the transmitting secondary mirror, and after being reflected by the transmitting secondary mirror, the fourth plane mirror and the fifth plane mirror in sequence, the reflected light reaches the main reflecting surface, and after being reflected by the main reflecting surface, the radius of the light beam is enlarged, so that parallel light beams are formed to irradiate the target to be measured.

The receiving compact range comprises a main reflecting surface, a fifth plane mirror and a receiving auxiliary mirror which are sequentially arranged; the optical signal reflected by the target to be measured reaches the main reflecting surface, sequentially passes through the main reflecting surface and the fifth plane mirror for reflection, reaches the receiving auxiliary mirror, is reflected by the receiving auxiliary mirror to form a parallel light beam reaching the fourth light splitting film, and the radius of the parallel light beam is reduced to the size before beam expansion.

Preferably, the detection component comprises a reference mixer, a test mixer and a vector network analyzer; the test mixer mixes the fed local oscillator measurement light and the signal measurement light to obtain a test intermediate frequency signal, and the reference mixer mixes the fed local oscillator reference light and the signal reference light to obtain a reference intermediate frequency signal; and the test intermediate frequency signal and the reference intermediate frequency signal are respectively input into a vector network analyzer, and the vector network analyzer analyzes to obtain RCS information of the target to be tested.

Preferably, the main reflecting surface, the transmitting auxiliary mirror and the receiving auxiliary mirror are off-axis parabolic mirrors with the same off-axis angle, the aperture and the focal length of the transmitting auxiliary mirror and the receiving auxiliary mirror are also the same, and the aperture range is within 100 mm-150 mm.

Preferably, the light source is a terahertz quantum cascade laser cooled by a Stirling refrigerator.

Preferably, the off-axis parabolic mirror is INVAR steel with a gold-plated surface.

Preferably, the incident surface of each level of the light splitting film is an inverted cone structure film prepared by a polystyrene glue homogenizing method and a needle tip metal mold hot stamping method.

Preferably, each flat mirror is INVAR steel with a gold-plated surface.

Preferably, the reference mixer and the test mixer are schottky diodes.

Preferably, the angle between the beam emitted by the emitting compact field and the beam received by the receiving compact field is very small, and can be less than 0.2 °.

In summary, compared with the prior art, the invention has the following advantages:

1. the target RCS measurement transmitting-receiving system is built based on a single terahertz quantum cascade laser, and has the advantages of small volume, simple light path structure, large quiet zone size and high light emission rate;

2. by means of coherent measurement, the amplitude and phase information of the target to be measured can be detected, the signal-to-noise ratio is high,

high sensitivity measurement of the target RCS can be achieved.

The conception and the specific configuration of the system of the present invention will be further described with reference to the accompanying drawings to fully understand the objects of the present invention.

Drawings

FIG. 1 is a light path diagram of a preferred embodiment of a quantum cascade based RCS measurement transceiver system of the present invention;

FIG. 2 is a light path diagram of an emission compact field in an embodiment;

FIG. 3 is a light path diagram of an embodiment for receiving compact fields.

Detailed Description

The present invention provides a quantum cascade-based RCS (RCS, radar cross section) measurement transceiver system, which is further described in detail with reference to the accompanying drawings and a preferred embodiment. It is to be noted that the following examples are only illustrative of the present invention, and do not limit the scope of the present invention. Similarly, the following embodiments are only some embodiments but not all embodiments of the invention, and the technical solutions that can be obtained by a person skilled in the art through logic analysis, reasoning or limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection determined by the claims.

As shown in fig. 1, fig. 1 is a light path diagram of a preferred embodiment of an RCS measurement transceiver system based on quantum cascade according to the present invention. The measurement transmitting and receiving system includes: the light source A1 is a quantum cascade laser with the model of easy QCL-110 and the frequency range of 1.8 THz-5 THz, and can emit light signals to a subsequent light path; the local oscillator optical path comprises a local oscillator reference optical path and a local oscillator measurement optical path, and optical signals emitted by the light source are transmitted in the local oscillator reference optical path and the local oscillator measurement optical path respectively to obtain local oscillator reference light and local oscillator measurement light; the signal light path comprises a signal reference light path and a signal measuring light path, and optical signals emitted by the light source are respectively transmitted in the signal reference light path and the signal measuring light path to obtain signal reference light and signal measuring light; the detection component comprises a test mixer M1, a reference mixer M2 and a vector network analyzer B1, and can mix and analyze optical signals obtained in an optical path to obtain RCS information of the target to be detected.

Wherein the signal measurement optical path comprises a compact range, and the compact range comprises an emission compact range and a reception compact range.

The local oscillation reference light path is composed of a beam shaping mirror R8, a fifth light splitting film S5, a sixth plane mirror R9, a third light splitting film S3, a seventh plane mirror R10, a second light splitting film S2 and a second lens L2 which are sequentially arranged; the local oscillation reference optical path is as follows: terahertz waves emitted by a quantum cascade laser A1 are firstly subjected to beam shaping through a beam shaping mirror R8 to form collimated light beams, then the collimated light beams are split through a fifth light splitting film S5, transmitted light split by the fifth light splitting film S5 is reflected through a sixth plane mirror R9 and reaches a third light splitting film S3, transmitted light split through the third light splitting film S3 is reflected through a seventh plane mirror R10 and a second light splitting film S2 in sequence and then reaches a second lens L2, and the focused transmitted light is fed into a reference mixer M2 as local oscillation reference light; while the transmitted beam passing through the second dichroic film S2 is absorbed by the pre-set first wave absorbing material.

The local oscillation measuring optical path is composed of a beam shaping mirror R8, a fifth light splitting film S5, a sixth plane mirror R9, a third light splitting film S3, a fourth light splitting film S4 and a first lens L1 which are sequentially arranged; the first half part of the local oscillation measuring optical path is the same as the first half part of the local oscillation reference optical path, namely the beam shaping mirror R8 sequentially passes through the fifth light splitting film S3 and the sixth plane mirror R9 and then reaches the third light splitting film S3, but after reaching the third light splitting film S3, a reflected light beam split by the third light splitting film S3 is reflected by the fourth light splitting film S4, and is focused by the first lens L1 to be fed into the testing mixer M1 as local oscillation measuring light; the light beam transmitted through the fourth light splitting film S4 is absorbed by the second wave-absorbing material arranged in advance.

The signal reference light path is composed of a beam shaping mirror R8, a fifth light splitting film S5, a first plane mirror R1, a second plane mirror R2, a first light splitting film S1, a second light splitting film S2 and a second lens L2 which are sequentially arranged; the signal reference optical path is specifically as follows: terahertz waves emitted by a quantum cascade laser A1 are firstly subjected to beam shaping through a beam shaping mirror R8 to form collimated light beams, then the collimated light beams are split through a fifth light splitting film S5, reflected light beams split by the fifth light splitting film S5 are reflected by a first plane mirror R1 and a second plane mirror R2 in sequence and then reach a first light splitting film S1, transmitted light beams of the first light splitting film S1 are transmitted through a second light splitting film S2 in sequence and focused through a second lens L2, and finally the reflected light beams serve as signal reference light to be fed into a reference mixer M2; the light beam reflected by the second dichroic film S2 is absorbed by the first wave absorbing material provided in advance.

The signal measuring light path is composed of a beam shaping mirror R8, a fifth light splitting film S5, a first plane mirror R1, a second plane mirror R2, a first light splitting film S1 and a compact range which are arranged in sequence; the front half part of the signal measurement optical path is the same as the front half part of the signal reference optical path, namely, the beam shaping mirror passes through the fifth light splitting film S5, the first plane mirror R1 and the second plane mirror R2 in sequence, then the optical path to the first light splitting film S1 is the same, but after reaching the first light splitting film S1, the reflected light of the first light splitting film S1 is used as an emission signal to enter a compact range, the terahertz waves after being expanded by the emission compact range irradiate a target completely, the received signal reflected by the target further passes through the receiving compact range to reach the fourth light splitting film S4, the transmitted light of the fourth light splitting film S4 is focused through the first lens L1 and is fed into the testing mixer M1 as signal measurement light; the light beam reflected by the fourth light-dividing film S4 is absorbed by the second wave-absorbing material arranged in advance.

As shown in fig. 2, fig. 2 is an emission compact range optical path diagram, which is composed of an emission secondary mirror R3, a fourth plane mirror R4, a fifth plane mirror R5 and a main reflecting plane R6, which are arranged in sequence, wherein the transmission route of the emission signal is as follows: the emission signal is fed from the emission sub-mirror R3, sequentially reflected by the fourth plane mirror R4 and the fifth plane mirror R5, reaches the main reflecting surface R6, and is emitted through the main reflecting surface R6 to fully irradiate the target. The emitting sub-mirror R3 and the main reflecting surface R6 are off-axis parabolic mirrors with the same off-axis angle, the focal length of the emitting sub-mirror R3 is ten times smaller than that of the main reflecting surface R6, and thus the main reflecting surface R6 and the emitting sub-mirror R3 form a afocal beam expanding system, and the beam expanding ratio is 1: 10. After beam expansion, the beam waist radius of the emitted light beam at the mouth surface of the main reflecting surface R6 is enlarged by 10 times compared with that at the mouth surface of the emission secondary mirror R3, so that the size of a dead zone is enlarged, namely the measurement range is enlarged.

As shown in fig. 3, fig. 3 is a diagram of an optical path of a receiving compact range, which is composed of a main reflecting surface R6, a fifth plane mirror R5 and a receiving sub-mirror R7 arranged in sequence, and a transmission optical path of a receiving signal reflected by a target therein is as follows: the received signal is reflected by the main reflecting surface R6, then reflected by the fifth plane mirror R5, and finally reflected by the receiving auxiliary mirror R7 to form a collimated light beam. The receiving sub-mirror R7 and the emitting sub-mirror R3 in the emission compact range are off-axis parabolic mirrors with the same caliber, the focal length of the receiving sub-mirror R7 is the same as that of the emitting sub-mirror R3, and the focal length of the receiving sub-mirror R7 and the focal length of the emitting sub-mirror R3 are both 10 times smaller than that of the main reflecting surface R6, so that the beam waist radii of the light beam before entering the emission compact range and the light beam emitted by the emission compact range are the same.

The test mixer M1 mixes the fed local oscillator measurement light and the signal measurement light, and the test intermediate frequency signal output after mixing enters a test intermediate frequency port of a vector network analyzer B1; the reference mixer M2 mixes the fed-in local oscillation reference light and the signal reference light, the mixed output reference intermediate frequency signal enters a reference intermediate frequency port of the vector network analyzer B1, and the vector network analyzer B1 analyzes the received test mixed frequency signal and the reference intermediate frequency signal by adopting a coherent measurement means, so as to obtain RCS data such as amplitude and phase information of a target to be measured, and realize high-sensitivity measurement of the target RCS.

In the present embodiment, after the terahertz wave emitted from the quantum cascade laser a1 is beam-shaped by the beam shaping mirror R8, the beam waist diameter of the formed collimated beam is 45 mm.

In this embodiment, the aperture of the main reflecting surface R6 is 1m, the focal length is 1866mm, the off-axis angle is 30 °, the aperture of the transmitting sub-mirror R3 is 120mm, the focal length is 186.6mm, the off-axis angle is 30 °, and after a transmitted signal is expanded by the afocal beam expanding system, the beam waist radius of the light beam at the aperture of the main reflecting surface R6 becomes 450 mm. The receiving secondary mirror R7 is an off-axis parabolic mirror with the aperture of 120mm, the focal length of 186.6mm and the off-axis angle of 30 degrees, as with the transmitting secondary mirror R3.

In this embodiment, the transmitting and receiving optical paths deviate from the ideal focal length of the main reflection surface R6 by +3.5mm and-3.5 mm, respectively, on the focal plane, and the focal plane scale is 1.7 angular/mm, so the angle between the incident beam and the return beam of the target to be measured is about 0.2 °.

In this embodiment, the object to be measured is placed on a foam stage, the center of the object is aligned with the center of the foam stage, the positional deviation is minimized, the foam stage is placed on a high-precision two-dimensional turntable, the height of the center of mass of the object is coincident with the height of the center of the beam emitted by the transmit compact field, and the beam is directed exactly on the vertical central axis of the turntable.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the present invention, and these modifications or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.