A Calibration Method for the Incident Wave Direction of a Terahertz Compact Range

Abstract

A calibration method for the incident wave direction of a terahertz compact range site determines the incident wave direction of the compact range site based on the overall optimization of the actual surface shape of the main reflector, levels the incident wave direction of the site based on the horizontal level of the ground, realizes the monitoring of the change of the incident wave direction of the site at any time, and calibrates the incident wave direction of the site. When measuring the electrical performance of a spaceborne antenna in a terahertz compact range, the incident wave direction of the site can be obtained quickly, non-contact, and with high precision, realizing the calibration of the site for the antenna under test.

Description

Technical Field

[0001] The invention relates to a method for calibrating the incoming wave direction of a terahertz compact field, and belongs to the technical field of antenna mechanical measurement. Background Art

[0002] The compact range is a test device that uses a correction unit to convert the spherical wave radiated by the feed horn into a plane wave at a close distance. The system structure is as follows: Figure 1 As shown, it consists of a main reflector, a sub-reflector and a feed assembly. When the satellite-borne antenna is tested in a compact field, the antenna to be tested needs to be calibrated on site. Field calibration generally aligns the satellite coordinate system or the antenna coordinate system in parallel with the incoming wave direction of the compact field. The correctness of the compact field calibration result, the accuracy of the calibration and the efficiency of the calibration directly affect the conclusion and efficiency of the electrical performance test of the antenna product. The correctness and accuracy of the field calibration and the calibration efficiency depend on the initial calibration result of the incoming wave direction of the compact field.

[0003] With the development of terahertz technology in recent years, many tasks involve the testing of terahertz antenna radiation performance. At present, most of the research on terahertz compact field in China is focused on its system design, structural composition and antenna test application, while there is less research on the key issue of determining the direction of incoming waves involved in its application process. Due to the protection of core technologies abroad, no relevant methods for calibrating the direction of incoming waves of terahertz compact field have been found. The terahertz compact field system imported into China is generally directly given the calibration result of the incoming wave direction by foreign manufacturers. When the antenna to be tested is calibrated in the compact field, the calibration result given by the manufacturer is directly used, and the origin and specific method of obtaining the calibration result are unknown. Therefore, it is currently impossible for China to retest and inspect the long-term stability of the incoming wave direction of the compact field by itself. When testing is required, it is generally necessary to contact the original manufacturer for on-site processing. Therefore, the calibration of the incoming wave direction of the terahertz compact field has become the key to subsequent applications. Summary of the invention

[0004] The technical solution of the present invention is: to overcome the shortcomings of the prior art, the present invention proposes a calibration method for the field wave direction of a terahertz compact field, a method for determining the field wave direction by measuring the optimal surface of the main and reverse electrodes, and completing the field wave direction calibration with the help of a geoid reference and a cubic mirror; the present invention can further obtain the field wave direction quickly, non-contact, and with high precision, thereby realizing the field calibration of the antenna to be tested.

[0005] The technical solution of the present invention is:

[0006] A method for calibrating the incoming wave direction of a terahertz compact field, comprising:

[0007] Reserve a reference hole on the main reflector for measuring the terahertz compact range, determine the site coordinate system; perform overall optimization of the actual surface shape of the main reflector, correct the site coordinate system, determine the incoming wave direction of the corrected site, and obtain the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system;

[0008] Establish a geodetic leveling coordinate system, and based on the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system, calculate the angular deviation between the incoming wave direction of the corrected site and the geodetic level; eliminate the angular deviation by adjusting the support structure of the compact range, level the incoming wave direction of the corrected site, and obtain the actual incoming wave direction of the site;

[0009] Calibrate the included angle in the geodetic horizontal plane between the actual incoming wave direction of the site and the normal direction of the vertical mirror surface of the reference cube mirror installed on the main reflector body of the compact range.

[0010] Preferably, determining the incoming wave direction of the corrected site and obtaining the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system includes:

[0011] (11) Through the measurement and calculation of the reserved reference hole on the main reflector, obtain the compact range site coordinate system and the incoming wave direction of the site;

[0012] (12) In the site coordinate system determined in (11), measure the surface of the reflector in the form of laser point-by-point light touch according to the measurement grid points on the surface of the main reflector, and obtain the three-dimensional coordinates of discrete multiple points on the surface;

[0013] (13) Perform overall surface shape optimization on the discrete measurement points of the shaped main reflector surface obtained in the site coordinate system determined in (11) and the theoretical model in the site coordinate system, obtain the actual optimal surface shape accuracy of the main reflector and the site coordinate system correction parameters, and obtain the incoming wave direction of the corrected site and the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system.

[0014] Preferably, in step (12), according to the operating frequency of the compact range, overall plan the measurement point grid on the surface of the main reflector, and the grid spacing is the wavelength corresponding to the operating frequency of the compact range.

[0015] Preferably, in step (13), the overall surface shape optimization of the main reflector adopts the least squares fitting method. By minimizing the root mean square of the normal deviation between the measured discrete points and the theoretical model surface, determine the translation and rotation amounts of the measured discrete points, and obtain the site coordinate system correction parameters.

[0016] Preferably, the number of reserved reference holes on the selected main reflector is more than 3.

[0017] Preferably, leveling the incoming wave direction of the corrected site includes:

[0018] (21) Establish a geodetic leveling coordinate system with a horizontal accuracy better than 1″; under the geodetic leveling coordinate system, use laser measurement to select the reference hole reserved for the main reflector, and perform a least-squares transformation with the measured value of the reference hole and the coordinate value of the reference hole in the corrected site coordinate system to determine the angular deviation between the corrected incoming wave direction of the site and the geodetic level.

[0019] (22) Adjust the height of the support points of the anechoic chamber support structure to achieve the height adjustment of the long side and the short side, and eliminate the angular deviation.

[0020] Preferably, calibrate the angle between the actual incoming wave direction of the site and the normal direction of a certain mirror surface of the reference cube mirror installed on the main reflector of the anechoic chamber, including:

[0021] (31) Use three theodolites T1, T2, and T3 to form a collimation measurement system based on the geodetic level. Theodolite T1 can be mutually sighted with theodolite T2 and theodolite T1 can be mutually sighted with theodolite T3.

[0022] (32) The two theodolites T1 and T2 perform intersection measurement to obtain the three-dimensional coordinates of the reference hole reserved for the selected main reflector. Based on the measured value of the reference hole and the coordinate value of the reference hole in the corrected site coordinate system, establish a corrected site coordinate system in the theodolite geodetic leveling coordinate system; the third theodolite T3 performs collimation measurement on a certain vertical mirror surface of the reference cube mirror.

[0023] (33) Theodolite T1 is mutually sighted with theodolite T2 and theodolite T1 is mutually sighted with theodolite T3 to obtain the angle between the normal direction of the vertical mirror surface of the reference cube mirror and the theodolite geodetic coordinate system on the geodetic level; according to the relationship between the corrected site coordinate system and the theodolite geodetic leveling coordinate system, obtain the angle between the theodolite geodetic coordinate system and the corrected site coordinate system on the geodetic level; based on the above two obtained angles, calculate the angle between the normal direction of the vertical mirror surface of the reference cube mirror and the actual incoming wave direction of the site on the geodetic level, and calibrate the actual incoming wave direction of the site onto the mirror surface of the reference cube mirror to obtain the angle between the actual incoming wave direction of the site and the normal direction of the vertical mirror surface of the reference cube mirror in the geodetic horizontal plane.

[0024] Preferably, in step (33), the angle between the actual incoming wave direction of the site and the normal of the vertical mirror surface of the reference cube mirror in the horizontal plane is calculated through the angle between the theodolite geodetic coordinate system and the corrected site coordinate system on the geodetic level and the collimation azimuth angle of the theodolite mutual sighting.

[0025] Preferably, after calibrating the incoming wave direction of the terahertz anechoic chamber site, when calibrating the test antenna site, establish a measurement coordinate system consistent with the direction of the terahertz anechoic chamber coordinate system, reproduce the incoming wave direction of the site, and realize the calibration of the test antenna and the incoming wave direction of the site.

[0026] Preferably, the angle between the incoming wave direction calibration and the reference cubic mirror calibration mirror normal direction in the horizontal plane is combined with the mutual aiming azimuth angle of the theodolite, and the theodolite measurement coordinate system is rotated to obtain a measurement coordinate system consistent with the direction of the terahertz compact field coordinate system.

[0027] The beneficial effects of the present invention compared with the prior art are:

[0028] (1) The present invention is the first domestic technology to propose a technology for calibrating the incoming wave direction of a terahertz compact field, breaking through the barriers to the protection of foreign core technologies. Domestic terahertz compact field users can retest and inspect the long-term stability of the incoming wave direction of the compact field by themselves, without having to rely on on-site processing by foreign manufacturers.

[0029] (2) The present invention proposes to determine the incoming wave direction of the compact field based on the overall optimization of the actual surface shape of the main reflector, thereby eliminating the deviation of the incoming wave direction of the field caused by the processing error of the reserved reference hole of the main reflector, the surface processing error and the deformation of the main reflector after installation.

[0030] (3) The present invention proposes a laser point-by-point touch measurement based on preset grid points, which can achieve uniform collection and measurement of the overall surface accuracy of the terahertz reflector under actual on-site installation conditions when the existing three-coordinate method, photogrammetry method, and optical scanning measurement method are all limited.

[0031] (3) The present invention proposes leveling of the incoming wave direction of the site based on the earth level, which realizes the real-time monitoring of the changes in the incoming wave direction of the site and facilitates the high-precision calibration and reproduction of the incoming wave direction of the site.

[0032] (4) The site wave direction extraction calibration proposed in the present invention does not require the introduction of theodolite elevation angle data during the calibration process, so that when the electrical performance of the satellite-borne antenna is measured in the terahertz compact field, the site wave direction can be obtained quickly, non-contact, and with high precision, thereby realizing the site calibration of the antenna to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A diagram of a measurement and calibration system according to an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of a measurement coordinate system and a site coordinate system of a laser testing system according to an embodiment of the present invention;

[0035] Figure 3 A grid measuring point map is preset for the main reflector surface of the embodiment of the present invention;

[0036] Figure 4 This is a cloud diagram for optimizing the overall surface shape of the main reflector according to an embodiment of the present invention;

[0037] Figure 5 This is a top view of the site incoming wave direction calibration measurement in an embodiment of the present invention. Detailed implementation manners

[0038] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, which are as follows:

[0039] A calibration method for the incoming wave direction of a terahertz compact range site proposed by the present invention enables rapid, non-contact, and high-precision acquisition of the incoming wave direction of the site during the electrical performance measurement of a spaceborne antenna in the terahertz compact range, realizing the calibration of the site of the antenna to be measured.

[0040] The terahertz compact range mentioned in the present invention includes a main reflector and a reference cube mirror located at an easily observable position around the main reflector body. Among them, reserved reference holes are provided on the main reflector, and the reference holes are evenly arranged around the reflector and there are at least four.

[0041] As Figure 1 shown, the main reflector of the terahertz compact range is tested by using a laser test system and a theodolite, and the specific steps are as follows:

[0042] (1) Based on the overall optimization of the actual surface shape of the main reflector, determine the incoming wave direction of the corrected compact range site

[0043] (11) Through the measurement and calculation of the reserved reference holes on the main reflector, obtain the site coordinate system of the compact range and the incoming wave direction of the site

[0044] Use the laser test system to measure multiple reserved reference holes on the main reflector to obtain the three-dimensional coordinates of the reference holes in the measurement coordinate system of the laser test system. Perform a least-squares transformation on the measured values of the reference holes and the designed theoretical values of the reference holes in the site coordinate system to determine the positional relationship between the measurement coordinate system of the laser test system and the site coordinate system. The principle is as Figure 2 shown:

[0045] The measurement coordinate system XtYtZt of the laser test system, the Xt axis points to the 0-degree direction of the horizontal dial, the Zt axis is perpendicular to the horizontal dial and points to the zenith direction, and the Yt axis forms a right-handed system with the Xt axis and the Zt axis; the site coordinate system XcYcZc, the Zc axis is parallel to the incoming wave direction, the Xc axis is perpendicular to the Zc axis and plumb upward, and the Yc axis forms a right-handed system with the Xc axis and the Zc axis. (Xti, Yti, Zti) are the three-dimensional coordinates of the i-th reference hole in the measurement coordinate system of the laser test system, and (xci, yci, zci) are the three-dimensional coordinates of the i-th reference hole in the site coordinate system. Use the differences in the three-dimensional coordinate values of the same set of sufficient number of reference holes in the above two coordinate systems to determine the conversion parameters between the two coordinate systems. The number of reference holes ≥ 3. Among them, (α0, β0, γ0) are rotation parameters, and (x0, y0, z0) are translation parameters.

[0046]

[0047] The translation and rotation conversion parameters (x0, y0, z0, α0, β0, γ0) between the measurement coordinate system of the laser test system and the site coordinate system are calculated. Based on these parameters and the measurement coordinate system of the laser test system, the initial design position of the site coordinate system can be determined, and the direction of the Zc axis of the site coordinate system is the initial designed incoming wave direction of the site.

[0048] (12) Under the site coordinate system determined in (11), according to the operating frequency of the compact range, a measurement point grid is overall planned on the surface of the main reflector at a specified spacing. For detailed features, the grid can be densified. The preset measurement point distribution is as Figure 3 shown. The laser test system is used to measure the surface of the reflector in a point-by-point light-touch measurement form according to the uniformly preset measurement grid points on the surface of the main reflector, and the discrete multi-point three-dimensional coordinates of the surface are obtained.

[0049] The optimization of the overall actual surface shape of the main reflector of the compact range is based on the high-precision measurement of its overall surface characteristics. The optimization of the overall actual surface shape of the main reflector of the compact range is based on the high-precision measurement of its overall surface characteristics. In the prior art, the three-coordinate method, photogrammetry method, optical scanning measurement method, etc. are widely used for measuring the surface shape accuracy characteristics of the reflector. Since the three-coordinate measurement method is applicable to the laboratory environment and has strict requirements for the placement state of the measured object, the main reflector of this compact range has also been measured for the surface shape accuracy by the three-coordinate method in the horizontal placement state when it is manufactured and shipped from the factory. However, for the main reflector of the compact range that has completed installation and calibration, such as Figure 1As shown, its actual installation state and measurement environment do not meet the measurement requirements of the coordinate measuring machine. Therefore, due to its own deformation after installation, the actual surface features cannot be obtained by the coordinate measuring method. The photogrammetry method for measuring the surface accuracy features requires the cooperation of special photogrammetric target points. The photogrammetric target points are divided into solid paste targets and optical projection virtual targets. Due to the high working frequency of the terahertz compact range, the designed surface accuracy of its main reflector is high, the surface is smooth, similar to a mirror state. If the photogrammetry method is used in combination with the solid paste target, the adhesive layer of the pasted target will seriously damage the surface state of the terahertz reflector. At the same time, the inconsistent thickness of the solid target itself will also cause non-negligible measurement errors to the surface accuracy of the terahertz reflector. When using the photogrammetry method in combination with the optical projection virtual target, due to the mirror-like characteristics of the reflector surface, the optical virtual target projection will produce specular reflection and the projection point coordinates cannot be obtained. Therefore, the photogrammetry method is also not applicable to the measurement of the surface features of the terahertz compact range main reflector. The optical scanning method for measuring the surface accuracy features generally has two types: contact and non-contact. The non-contact method obtains the surface accuracy features through laser surface projection photography. Similarly, due to the specular reflection characteristics of the terahertz reflector, the non-contact scanning measurement method is not applicable. The contact scanning measurement method uses a laser measurement system in combination with a standard target prism. By contacting and continuously moving the target prism with the reflector surface, the laser measurement system can obtain the coordinates of the target prism in real time and then scan to obtain the surface features of the reflector. However, the contact continuous movement scanning method has the risk of scratching and damaging the reflector surface, and this method also has its limitations.

[0050] In order to accurately measure the overall surface features of the compact range main reflector, a laser point-by-point gentle touch measurement method based on preset grid points is proposed, which realizes the uniform acquisition and measurement of the overall surface accuracy of the terahertz reflector in the actual on-site installation state under the condition that the existing coordinate method, photogrammetry method, and optical scanning measurement method are all limited. By presetting the grid measurement points in advance, the uniform distribution of the measurement points on the shaped reflector surface is ensured, which helps to reflect the real surface characteristics and local detail features, and also avoids the scratching of the reflector surface by the scanning measurement method of the laser test system.

[0051] (13) The discrete measurement points of the shaped main reflector surface obtained in the site design coordinate system determined in (11) are optimized for the overall surface shape with the theoretical model in the site design coordinate system. Using the least squares fitting method, mainly by minimizing the root mean square of the normal deviation between the measured discrete points and the theoretical model surface, the translation and rotation amounts of the measured discrete points are determined. The rotation parameters are (α1, β1, γ1), the translation parameters are (x1, y1, z1), XcYcZc is the initial site design coordinate system, Xc’Yc’Zc’ is the corrected site coordinate system, (xci, yci, zci) are the three-dimensional coordinates of the reference holes in the initial site design coordinate system, and (xci’, yci’, zci’) are the three-dimensional coordinates of the reference holes in the corrected site coordinate system.

[0052]

[0053] The actual optimal surface accuracy of the main reflector and the site coordinate system correction parameters (x1, y1, z1, α1, β1, γ1) are obtained. As Figure 4 shown in the contour map of the main reflector surface state, the overall RMS is 15μm. With these parameters, the processing error of the reserved reference holes of the main reflector, the surface processing error, and the deviation of the incoming wave direction of the site caused by its own deformation after installation can be corrected, and the corrected incoming wave direction of the site can be obtained. At the same time, the coordinate values of the reserved reference holes of the main reflector can be corrected to obtain a new set of design values of the reserved reference holes of the main reflector in the corrected site coordinate system. Subsequently, when calibrating the actual incoming wave direction of the site, the corrected reference holes can be used for measurement conversion.

[0054] Compared with the prior art, through the optimization and correction of the overall actual surface shape of the main reflector, the problem that the obtained incoming wave direction of the site has a large deviation from the actual incoming wave direction of the anechoic chamber due to the influence of the processing error of the reserved reference holes, the processing error of its own surface, and its own deformation after actual installation is avoided.

[0055] (2) Based on the incoming wave direction of the site leveled by the earth

[0056] After determining the actual accurate incoming wave direction of the compact range site through the above steps, in order to be able to monitor the change of the actual site incoming wave direction at any time during the later use process and facilitate the high-precision calibration of the site incoming wave direction, this patent proposes a method for leveling the site incoming wave direction based on the earth's horizontal plane. That is, after obtaining the corrected site incoming wave direction from the optimal surface shape of the main reflector, the site incoming wave direction is adjusted to be parallel to the ground plane with the earth's horizontal plane as the absolute reference. That is, the Zc axis and Yc axis of the site coordinate system are parallel to the earth's horizontal plane. During the subsequent use of the compact range, the change amount of the site incoming wave direction can be evaluated at any time by establishing a reference coordinate system of the earth's horizontal plane, providing monitoring data for the stability of the compact range. At the same time, for the site incoming wave direction leveled with the earth's horizontal plane, the calibration and reproduction of the incoming wave direction can be carried out only through the measurement of the azimuth angle of the theodolite. During the process, the pitch angle data of the theodolite does not need to be introduced, simplifying the process of calibrating and reproducing the site incoming wave direction and reducing the error sources.

[0057] (21) Calculate the angular deviation between the corrected site incoming wave direction and the earth's horizontal plane

[0058] Based on the laser test system, establish a reference coordinate system for measuring the earth's horizontal plane with a horizontal accuracy of 1″. The axis directions of this reference coordinate system for measuring the earth's horizontal plane are generally consistent with those of the compact range site coordinate system. Under the reference coordinate system for measuring the earth's horizontal plane, use the laser test system to measure multiple reference holes reserved on the main reflector, and perform a least-squares transformation with the measured values of the reference holes and the new design values under the corrected site coordinate system to determine the translation and rotation transformation parameters (x2, y2, z2, α2, β2, γ2) between the reference coordinate system for measuring the earth's horizontal plane of the laser test system and the corrected site coordinate system. The rotation parameters β2 and γ2 are the angular deviations between the corrected site incoming wave direction and the earth's horizontal plane. Xt’Yt’Zt’ is the reference coordinate system for measuring the earth's horizontal plane of the laser test system, Xc’Yc’Zc’ is the corrected site coordinate system, (Xti’, Yti’, Zti’) is the three-dimensional coordinate of the reference hole under the reference coordinate system for measuring the earth's horizontal plane of the laser test system, and (xci’, yci’, zci’) is the three-dimensional coordinate of the reference hole under the corrected site coordinate system.

[0059]

[0060] (22) Eliminate the angular deviation

[0061] By adjusting the height of the 4 support points of the compact range support structure to achieve the height adjustment of the long side and short side, the angular deviations β2 and γ2 can be eliminated. The specific method for determining the adjustment amount is as follows:

[0062] Δ1 / L = tanβ2, Δ2 / W = tanγ2

[0063] Among them, Δ1 and Δ2 are the height adjustment amounts of the short side and long side of the support structure, and L and W are the lengths of the long side and short side of the support structure.

[0064] Through adjustment, the parallelism between the incoming wave direction in the actual site and the ground plane can be achieved with a high precision of better than 0.001°, which can meet the subsequent requirements of incoming wave direction monitoring, calibration and reproduction in the compact site.

[0065] (3) The incoming wave direction of the site is derived and calibrated to the reference cubic mirror

[0066] After the actual incoming wave direction of the compact field is determined and leveled, in order to perform field calibration of the antenna to be tested in the terahertz compact field for subsequent electrical performance testing, improve the correctness, accuracy and efficiency of the field calibration, and avoid the difficulty and complexity of the process of using the laser test system to measure the main reflector reference hole to establish the field coordinate system to determine the incoming wave direction after the terahertz compact field is built, as well as the impact of contact measurement on the compact field test system, this patent proposes a field incoming wave direction extraction calibration method, that is, calibrate the angle between the actual field incoming wave direction and the normal direction of a certain mirror surface of the reference cubic mirror installed on the main reflector body of the compact field on the geoid. When calibrating the field of the antenna to be tested, with the help of the high-precision self-collimation function of the theodolite system and the establishment function of the geoid horizontal measurement coordinate system, the horizontal azimuth of the normal direction of the calibrated mirror surface of the cubic mirror under the theodolite system is collimated, and the field incoming wave direction can be quickly, accurately, and highly accurately re-contacted in a non-contact manner through the angle with the calibrated field incoming wave direction, thereby completing the calibration of the antenna to be tested and the field incoming wave direction. This calibration method is different from the traditional antenna reference mirror calibration. It does not require the alignment of two adjacent vertical surfaces of the cubic mirror, and the calibration process does not require the introduction of theodolite elevation angle data.

[0067] Three theodolites are used to form a geodetic intersection and alignment measurement system, such as Figure 1 As shown, theodolite T1 and theodolite T2 are intersected to obtain the three-dimensional coordinates of the reserved reference hole of the main reflector. The reference hole measurement value and the new design value of the reference hole in the corrected site coordinate system are transformed by least squares to establish the corrected site coordinate system Xc'Yc'Zc' in the theodolite geodetic coordinate system XmYmZm. Theodolite T3 is collimated to measure the mirror surface of the reference cubic mirror Zj. Among them, the geodetic coordinate system of the theodolite is XmYmZm, the Xm axis points from T1 to the projection of T2 on the horizontal disk of T1, that is, the projection on the geodetic plane, the Zm axis is perpendicular to the horizontal disk of T1 and the plumb bob is upward, and the Ym axis forms a right-handed system with the Xm axis and the Zm axis. The reference cubic mirror coordinate system is XjYjZj, the Zj axis and the Yj axis are parallel to the normal directions of the two adjacent mirror surfaces, and the Xj axis forms a right-handed system with the Yj axis and the Zj axis.

[0068] like Figure 5As shown in the figure, the theodolite T1 and theodolite T2, and the theodolite T1 and theodolite T3 are sighted at each other. According to the principle of azimuth angle transfer by mutual sighting, the angle between the Zj axis of the reference cube mirror and the Xm axis of the theodolite geodetic horizontal coordinate system on the geodetic horizontal plane can be obtained. At the same time, according to the relationship between the modified site coordinate system and the theodolite geodetic horizontal measurement coordinate system, the angle between the Xm axis of the theodolite geodetic horizontal coordinate system and the Zc axis of the modified site coordinate system on the geodetic horizontal plane can be obtained. Thus, the angle between the Zj axis of the reference cube mirror and the Zc axis of the modified site coordinate system on the geodetic horizontal plane can be further obtained, that is, the actual incoming wave direction of the site is calibrated onto the Zj plane of the reference cube mirror. The angle ∠4 between the actual incoming wave direction of the site and the normal of the Zj plane of the reference cube mirror in the horizontal plane can be calculated through the angle ∠1 between the Xm axis of the theodolite measurement coordinate system and the Zc axis of the modified site coordinate system, and the mutual sighting azimuth angles ∠2 and ∠3 of the theodolites.

[0069] So far, the calibration of the final incoming wave direction of the terahertz compact range site has been completed.

[0070] During the subsequent calibration of the antenna site to be measured, the Zj plane of the reference cube mirror is collimated and measured by the theodolite system. By rotating the theodolite measurement coordinate system according to the incoming wave direction calibration angle ∠4 and the mutual sighting azimuth angles ∠2 and ∠3 of the theodolites, a measurement coordinate system consistent with the direction of the terahertz compact range coordinate system can be established, thus accurately reproducing the incoming wave direction of the site.

[0071] For the convenience of describing the present invention and simplifying the description, the measurement coordinate system of the laser test system, the site coordinate system, the reference cube mirror coordinate system, and the theodolite geodetic horizontal coordinate system are defined. This definition method is not the only definition method. The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A calibration method for the incoming wave direction of a terahertz compact range site, characterized in that, Including: Reserving a reference hole on the main reflector for measuring the terahertz compact range, and determining the site coordinate system; Conducting overall optimization of the actual surface profile of the main reflector, correcting the site coordinate system, determining the incoming wave direction of the corrected site, and obtaining the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system; Establishing a geodetic leveling coordinate system, calculating the angular deviation between the incoming wave direction of the corrected site and the geodetic level based on the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system; eliminating the angular deviation by adjusting the support structure of the compact range, and leveling the incoming wave direction of the corrected site to obtain the actual incoming wave direction of the site; Calibrating the included angle in the geodetic horizontal plane between the actual incoming wave direction of the site and the normal direction of the vertical mirror surface of the reference cube mirror installed on the main reflector of the compact range, including: (31) Using three theodolites T1, T2, and T3 to form an intersection collimation measurement system based on the geodetic horizontal plane, and theodolite T1 can be mutually aimed at theodolite T2 and theodolite T1 can be mutually aimed at theodolite T3; (32) Measuring the three-dimensional coordinates of the selected reserved reference hole on the main reflector by the intersection measurement of two theodolites T1 and T2, and establishing a corrected site coordinate system in the theodolite geodetic horizontal measurement coordinate system based on the measured values of the reference hole and the coordinate values of the reference hole in the corrected site coordinate system; the third theodolite T3 collimates and measures a certain vertical mirror surface of the reference cube mirror; (33) Theodolite T1 is mutually aimed at theodolite T2 and theodolite T1 is mutually aimed at theodolite T3 to obtain the included angle between the normal direction of the vertical mirror surface of the reference cube mirror and the theodolite geodetic horizontal coordinate system on the geodetic horizontal plane; according to the relationship between the corrected site coordinate system and the theodolite geodetic horizontal measurement coordinate system, obtain the included angle between the theodolite geodetic horizontal coordinate system and the corrected site coordinate system on the geodetic horizontal plane; based on the above two obtained included angles, calculate the included angle between the normal direction of the vertical mirror surface of the reference cube mirror and the actual incoming wave direction of the site on the geodetic horizontal plane, and calibrate the actual incoming wave direction of the site onto the mirror surface of the reference cube mirror to obtain the included angle between the actual incoming wave direction of the site and the normal direction of the vertical mirror surface of the reference cube mirror in the geodetic horizontal plane.

2. The calibration method for the incoming wave direction of a terahertz compact range site according to claim 1, wherein: Determining the incoming wave direction of the corrected site and obtaining the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system, including: (11) Through the measurement and calculation of the reserved reference hole on the main reflector, obtain the compact range site coordinate system and the incoming wave direction of the site; (12) Under the site coordinate system determined in (11), measure the surface of the reflector in the form of laser point-by-point light touch according to the measurement grid points on the surface of the main reflector, and obtain the three-dimensional coordinates of discrete multiple points on the surface; (13) Optimize the overall surface profile of the shaped main reflector discrete measurement points obtained under the site coordinate system determined in (11) and the theoretical model under the site coordinate system to obtain the actual optimal surface accuracy of the main reflector and the site coordinate system correction parameters, and obtain the incoming wave direction of the corrected site and the coordinate values of the reserved reference hole on the main reflector in the corrected site coordinate system.

3. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 2, characterized in that: In step (12), according to the operating frequency of the compact range, overall plan the measurement point grid on the surface of the main reflector, and the grid spacing is the wavelength corresponding to the operating frequency of the compact range.

4. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 2, characterized in that: In step (13), the overall surface shape optimization of the main reflector adopts the least squares fitting method. By minimizing the root mean square of the normal deviation between the measured discrete points and the theoretical model surface, the translation and rotation amounts of the measured discrete points are determined, and the correction parameters of the site coordinate system are obtained.

5. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 1, characterized in that: The number of reserved reference holes for the selected main reflector is more than 3.

6. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 1, characterized in that: Level the incoming wave direction of the site after correction, including: (21) Establish a geodetic leveling coordinate system with a horizontal accuracy better than 1″; under the geodetic leveling coordinate system, use a laser to measure the reserved reference holes of the selected main reflector, and perform a least squares transformation with the measured values of the reference holes and the coordinate values of the reference holes in the corrected site coordinate system to determine the angular deviation between the corrected incoming wave direction of the site and the geodetic level. (22) Adjust the height of the long side and the short side by adjusting the height of the fulcrum of the compact range support structure to eliminate the angular deviation.

7. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 1, characterized in that, In step (33), the included angle between the actual incoming wave direction of the site and the normal of the vertical mirror surface of the reference cube mirror in the horizontal plane is calculated through the included angle between the theodolite geodetic horizontal coordinate system and the corrected site coordinate system on the geodetic horizontal plane and the mutual aiming azimuth angle of the theodolite.

8. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 1, characterized in that: After completing the calibration of the incoming wave direction of the terahertz compact range site, when calibrating the antenna under test on the site, establish a measurement coordinate system consistent with the direction of the terahertz compact range coordinate system, reproduce the incoming wave direction of the site, and realize the calibration of the antenna under test and the incoming wave direction of the site.

9. A calibration method for the incoming wave direction of a terahertz compact range site according to claim 8, characterized in that: According to the included angle between the calibration of the incoming wave direction and the normal direction of the calibration mirror surface of the reference cube mirror in the horizontal plane, combined with the mutual aiming azimuth angle of the theodolite, rotate the theodolite measurement coordinate system to obtain a measurement coordinate system consistent with the direction of the terahertz compact range coordinate system.

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