A large passive intermodulation darkroom test method

Abstract

A large passive intermodulation darkroom test method belongs to the technical field of microwave antenna test. According to the unique test method of large passive intermodulation darkroom (20m(L)x20m(W)x20mm(H) or more), the test system calibration, antenna radiation power coverage, antenna radiation coverage area and other problems need to be considered. In view of the above problems existing in the PIM darkroom, a grid coverage test method is designed. On the basis of the grid segmentation, a system self-calibration method is proposed by using low intermodulation smooth aluminum plate to simulate the full reflection state of the antenna. The distance between the calibration antenna and the wave absorbing material is compensated to realize the maximum gain of the antenna, and the antenna gain and the appropriate transmitting power are realized. Based on the 3dB bandwidth of the antenna, the grid division of the antenna radiation area layout is adopted to realize the comprehensive coverage of the test power of the large darkroom.

Description

TECHNICAL FIELD

[0001] The application relates to a large passive intermodulation darkroom test method and belongs to the technical field of microwave antenna testing. BACKGROUND

[0002] Passive intermodulation (PIM for short) refers to a phenomenon that, under the condition of high power, when two or more than two carriers are input, carrier signals are modulated with each other due to the nonlinearity of a microwave passive component, and a combination product of the carrier frequencies falls into a receiving passband to cause interference.

[0003] With the rapid development of communication, space science and earth observation, more and more application satellites are needed, and large antennas of the satellites are increasingly demanded, and the size of the antennas is increasingly required to improve the signal transmission capacity and reduce the ground receiving device. The antenna net surface aperture is from several meters to more than one hundred meters, and needs to have high-precision reflection characteristics to meet high-frequency operation. Due to the limitation of the carrying capacity of space vehicles, the antennas are generally folded and fixed in the space vehicles, and then unfolded into a working state after the space vehicles enter the orbit. The large deployable antenna includes a net-shaped deployable antenna, a deployable planar array antenna, a petal-shaped solid surface deployable antenna, a flexible self-rebound antenna and an inflatable antenna.

[0004] The metal net-shaped deployable antenna has been widely used abroad, and most of the antennas with an aperture of more than ten meters are net-shaped deployable antennas. The metal net-shaped antenna has the characteristics of large unfolded aperture, light weight, wide frequency coverage, good elasticity, relative softness, very large volume contraction ratio, high forming precision, stable performance, high working reliability and wide application. The progress of the net technology of the deployable antenna, the performance of the net surface and the application working characteristics have become the key to determine the performance, efficiency and service life of the spaceborne antenna, and have become the research direction of the deployable antenna of each country.

[0005] However, the number of broken ends, defects and uniformity of the metal net in each direction directly affect the electrical performance of the antenna. The passive intermodulation performance of the metal net is not only related to the broken ends and defects of the metal net, but also related to the material, plating layer and weaving parameters of the net wire. Mastering the advanced process technology of the metal net is the key to developing the satellite transceiver shared net-shaped deployable antenna, and the research in this regard must be strengthened, so a large PIM darkroom needs to be built for model test verification and research.

[0006] The PIM darkroom design meets the echo-free environment of the PIM measurement function, and the darkroom wave absorption aims to create an ideal, reflection-free free space environment for electromagnetic wave radiation and propagation. A large PIM darkroom can realize the PIM performance test of a large antenna and an antenna reflector, and the PIM performance of the darkroom is tested after construction, which is the first measure to verify the environment. The PIM darkroom design meets the echo-free environment of the PIM measurement function, and the darkroom wave absorption aims to create an ideal, reflection-free free space environment for electromagnetic wave radiation and propagation. The design and installation of the absorbing material meet the effective coverage and shielding of the hidden PIM source in the darkroom, and the implementation process meets the continuous consistency of the installation surface of the absorbing material, and tries to reduce the hidden PIM caused by the sudden change and discontinuity of the shape structure due to installation.

[0007] The frequency range used by the present darkroom is 0.2GHz-40GHz, and the size is more than 20 meters in length, width and height. The problems in the test are:

[0008] 1) How to ensure that the power is uniformly distributed on the wall, and at the same time, the PIM signal generated by the wall can be received and detected.

[0009] 2) How to ensure that there is no missed point in the large-area wall test, and all tests are completed. SUMMARY

[0010] The technical problem solved by the present application is to overcome the shortcomings of the prior art and provide a large-scale passive intermodulation darkroom test method. By designing a large-scale passive intermodulation darkroom PIM performance test method, the problems of system calibration under the radiation state of the existing large PIM darkroom and power coverage are solved.

[0011] The technical solution of the present application is a large-scale passive intermodulation darkroom test method, comprising:

[0012] According to the size and test index requirements of the darkroom and the installation position of the darkroom design, the main radiation surface is determined or the test wall surface is selected as the test target wall surface according to the customer's requirements;

[0013] A radiation type passive intermodulation test system is built;

[0014] The radiation type passive intermodulation test system is calibrated;

[0015] According to the power test, the test position is calculated, the test layout point is calculated according to the antenna beam width, the offset test is set at the same point, and the tests of different points are completed in turn.

[0016] Further, the radiation type passive intermodulation test system comprises two signal source links, a frequency synthesizer, a duplexer, an antenna, a receiving link and a darkroom provided with a test target wall surface;

[0017] Each signal source link includes a signal source, a continuous wave amplifier and a directional coupler; the signal source is used to generate a test signal for testing; the continuous wave amplifier is used to amplify the test signal; and the directional coupler is used to couple a high-power signal on the link, and the coupled signal enters a power meter to monitor input power;

[0018] The frequency synthesizer is used to synthesize two amplified signals into one signal;

[0019] The Tx / Rx duplexer receives the signal synthesized by the frequency synthesizer, and sends the signal to the antenna through the Tx transmission channel; the transmitted power signal is radiated to the wall, and the PIM signal generated by the wall is received by the antenna and sent to the receiving link;

[0020] The receiving link is used to receive the PIM signal generated by the wall and received by the antenna;

[0021] The power signal transmitted by the signal source link enters the antenna, and the antenna radiates the power signal to the darkroom wall; meanwhile, the antenna receives the PIM signal generated by the wall, and after receiving, the antenna filters out the transmission signal and noise signal through the Rx receiving filter, and then amplifies the signal through the low-noise amplifier and sends it to the spectrum analyzer for observation.

[0022] Further, the antenna is a shared antenna for radiation and transmission, or two separate antennas for transmission and reception.

[0023] Further, the power meter is connected to the coupling end of the directional coupler, and is used to read the power level value at the entrance of the measured object; when the bias value of the power meter is calibrated, an attenuator and a probe are connected at the entrance of the antenna, and by adjusting the bias value of the power meter, the reading of the power meter is consistent with the reading of the power meter connected to the probe.

[0024] Further, the bias value of the spectrum analyzer is determined by instrument measurement at the PIM test frequency point, which includes the gain of the low-noise amplifier and the insertion loss of the connecting cable and the receiving filter; a rated low-level signal is simulated by a microwave signal source and transmitted through the receiving link, and the spectrum analyzer receives to calibrate the spectrum analyzer receiving bias value of the receiving link.

[0025] Further, the calibration of the radiating passive intermodulation test system includes:

[0026] A flat aluminum plate is placed at the position where the metal mesh is placed, to simulate the ideal full reflection state of antenna radiation, and the test value of this test is the test value of the test system itself;

[0027] The test system verifies the capture ability of the PIM signal, to ensure that the test ability of the test system is normal.

[0028] Further, the calibration of the radiation passive intermodulation test system further comprises: placing a piece of steel wire mesh test produced PIM signal of the same size, verifying the ability of the test system to test PIM signal.

[0029] Further, according to the main radiation size of the darkroom, the antenna is placed at the geometric center of the darkroom, the radiation range and the radiation power spectral density are calculated according to the performance of the test antenna, and the distance test is adjusted.

[0030] Further, according to the test requirements, the corresponding power spectral density is selected and the corresponding test point layout is calculated, and the test target wall surface is divided into a plurality of grids, and each grid is tested to realize sufficient area coverage of the test target wall surface radiation.

[0031] Further, within 60° of the azimuth angle, three directions, left, right and center, are set to realize offset testing, and the same power positioning point is ensured to realize coverage of the transmission and reception power in different directions.

[0032] Compared with the prior art, the advantages of the present application are:

[0033] (1) System self-calibration method

[0034] The system itself test ability calibration is realized by placing a piece of smooth aluminum plate on the tested wall surface position, which is considered as the ideal reflection state of the antenna, and the test calibration value is the system test value. The test system tests the sensitivity, fast capture PIM signal ability, and ensures the normal system test ability. After testing the system performance by placing the metal aluminum plate, a piece of steel wire mesh (easy to produce large PIM level value) of the same size is placed to test the generated PIM value, and the system test to PIM ability is verified.

[0035] (2) Compensate the maximum gain of the antenna by calibrating the distance between the antenna and the wave-absorbing material

[0036] In order to ensure that enough radio frequency energy is radiated to the darkroom wall, a high gain antenna needs to be placed in the center of the darkroom, and a series of high gain antennas need to be configured in the test system. The difficulties faced are: first, it is a great challenge to design a high gain low PIM antenna, and second, the beam width of the high gain antenna is generally narrow. The maximum gain of the antenna is compensated by calibrating the distance between the antenna and the wave-absorbing material, so as to realize the achievable antenna gain and the appropriate transmission power.

[0037] (3) Ensure the wall test point coverage by using grid layout method based on the antenna radiation range

[0038] The size of the dark room is large, and the area of the single antenna radiation is limited, so that the number of points is arranged properly to ensure that the wall surface to be tested can be detected. In the method, the grid division is arranged based on the 3dB bandwidth of the antenna, and the radiation area of the antenna is arranged to realize comprehensive coverage.

[0039] (4) The antenna is rotated by 60° to realize the comprehensiveness of the transmitting and receiving angles

[0040] The radiation power and the grid coverage method realize the scanning coverage of the area, and when the same test point position is determined, the directivity of the received PIM signal is considered, the receiving and transmitting antennas are rotated by 60° at the same point to realize the 60° position rotation. In the 60° azimuth angle, three directions are set, and the left, middle and right are respectively 60° to realize the bias test. BRIEF DESCRIPTION OF DRAWINGS

[0041] Fig. 1 It is a schematic diagram of the radiation type passive intermodulation test system of the application.

[0042] Fig. 2 It is a schematic diagram of the PIM dark room coverage test layout (yoz) of the application.

[0043] Fig. 3 It is a schematic diagram of the angle layout (yoz) of the PIM dark room test antenna at different positions of the application. DETAILED DESCRIPTION

[0044] In order to better understand the above technical solutions, the technical solutions of the application will be described in detail below by means of the accompanying drawings and specific embodiments. It should be understood that the embodiments of the application and the specific features in the embodiments are detailed descriptions of the technical solutions of the application, and are not limitations of the technical solutions of the application. In the case of no conflict, the technical features in the embodiments of the application and the embodiments can be combined with each other.

[0045] The large passive intermodulation dark room test method provided by the embodiments of the application will be further described in detail below in combination with the accompanying drawings of the specification. The specific implementation manner can include (for example Figs. 1-3The system self-calibration problem under the radiation state is shown): to achieve the radiation state calibration and test sensitivity calibration as much as possible, a smooth and smooth metal aluminum plate is placed on the position of the wall to be tested, and this state is considered as the ideal reflection state of the antenna. The test calibration value is the system test value. The test system tests the sensitivity and quickly captures the PIM signal capability, and ensures the normal system test capability. After placing the metal aluminum plate to test the system performance, a steel wire mesh of the same size (which is easy to produce a large PIM level) is placed to test the PIM value, and the system's ability to capture and test PIM is verified. In order to ensure that enough radio frequency energy is radiated to the darkroom wall, a high-gain antenna needs to be placed in the center of the darkroom, and a series of high-gain antennas need to be configured in the test system. The difficulties faced are: first, it is a great challenge to design a high-gain low-PIM antenna, and second, the beam width of the high-gain antenna is generally narrow. The distance between the moving calibration antenna and the wave-absorbing material is calculated to compensate for the maximum gain of the antenna, so as to realize the achievable antenna gain and the appropriate transmission power. The size of the darkroom is large, and the area radiated by a single antenna is limited, so a suitable number of points need to be laid out to ensure that the test wall can be detected. In this method, the grid division is based on the 3dB bandwidth of the antenna, and the antenna radiation area is laid out to achieve full coverage. The radiation power and the grid coverage method realize the scanning coverage of the area, and when corresponding to the same test point position, the directivity of the received PIM signal is considered, and the receiving and transmitting antennas are rotated by 60° at the same point. In the 60° azimuth angle, three directions are set, and the left, middle and right are respectively 60° to realize the offset test.

[0046] Specifically, according to the unique test method of large-scale passive intermodulation darkroom (5m(L)x5m(W)x5mm(H) or more) which is different from small PIM darkroom, the test system calibration, antenna radiation power coverage, antenna radiation coverage area and other problems need to be considered. In view of the above problems existing in the PIM darkroom, a grid coverage test method is designed, and on the basis of the segmented grid, a system self-calibration method is proposed by using a low-intermodulation smooth metal aluminum plate to simulate the full reflection state of the antenna. The distance between the calibration antenna and the wave-absorbing material is compensated to realize the achievable antenna gain and the appropriate transmission power. The grid division is based on the 3dB bandwidth of the antenna, and the antenna radiation area is laid out to achieve full coverage of the large darkroom test power. When corresponding to the same test point position, the directivity of the received PIM signal is considered, and the receiving and transmitting antennas are rotated by 60° at the same point. In the 60° azimuth angle, three directions are set, and the left, middle and right are respectively 60° to realize the offset test, and ensure the receiving comprehensiveness in the test azimuth direction.

[0047] Further, the system self-calibration method mainly verifies two aspects. On the one hand, it verifies the system's ability to capture the PIM signal of the corresponding frequency sensitively and quickly. On the other hand, it verifies that the PIM level value of the system in the ideal state is superior to the performance of the measured piece by a certain order of magnitude, which can meet the test requirements. The system's own test ability calibration is to place a smooth and flat aluminum plate on the wall position to be tested. This state is considered to simulate the ideal reflection state of the antenna. The test value is the system PIM performance test value. The test system verifies the ability of the test system to capture PIM signals sensitively and quickly, and ensures that the system test ability is normal. After testing the performance of the system by placing the aluminum plate, a steel wire mesh of the same size (which can easily produce a larger PIM level value) is placed to test the PIM value generated, and the system's ability to test PIM is verified.

[0048] Further, in order to ensure that sufficient radio frequency energy is radiated to the darkroom wall, a high-gain antenna needs to be placed in the center of the darkroom. A series of high-gain antennas need to be configured in the test system, which faces the following difficulties: first, it is a great challenge to design a high-gain low-PIM antenna, and second, the beam width of the high-gain antenna is generally narrow. The distance between the calibration antenna and the wave-absorbing material is compensated for the maximum gain of the antenna to achieve the achievable antenna gain and the appropriate transmission power.

[0049] In the scheme provided in the embodiments of the present application, the following is included:

[0050] 1. According to the size of the darkroom and the test index requirements, and the installation position of the darkroom design, determine the main radiation surface as the test target or select the test wall surface according to the customer's requirements.

[0051] 2. Select the test method:

[0052] Since the test of a large PIM darkroom needs to be laid out for multi-point testing, if multiple antennas are erected, the interference between the antennas will be chaotic, and the position adjustment will be inconvenient. Therefore, in the present method, a single antenna test method is recommended for testing, and the test method is as follows: Fig. 1 .

[0053] 3. Test system calibration:

[0054] System calibration, mainly to verify two aspects of content, on the one hand to verify the system to the corresponding frequency of PIM signal can be sensitive and fast capture ability. On the other hand to verify the test system in the proximity of the ideal radiation state system PIM level value is superior to the performance of the measured piece of a certain order of magnitude, can meet the test requirements. System calibration is placed in the position of the metal net placed a flat aluminum plate, this state is considered to be the ideal antenna radiation of full reflection state. The value of this test is the system itself test value. To verify the test system test sensitive and fast capture ability, to ensure the system test ability normal. After placing the aluminum plate test system performance, placing a piece of steel wire mesh (easy to produce a larger PIM level) test PIM value, to verify the system test to PIM ability.

[0055] 4. According to the gain distance compensation method, the corresponding power spectral density and the corresponding radiation range are calculated.

[0056] According to the size of the main radiation surface of the darkroom, the antenna is placed in the geometric center of the darkroom, the radiation range and the radiation power spectral density are calculated according to the performance of the test antenna, and the distance test is adjusted. In order to ensure that enough radio frequency energy is radiated to the wall of the darkroom, we need to place a high gain antenna in the center of the darkroom, and a series of high gain antennas need to be configured in the test system. The difficulties faced are: first, it is a great challenge to design a high gain low PIM antenna, second, the beam width of high gain antenna is generally narrow, and the maximum gain of the antenna is compensated by adjusting the distance between the calibration antenna and the wave absorbing material, so as to realize the achievable antenna gain and the appropriate transmission power. The engineering implementation faces problems. The method uses a low gain, low PIM antenna as a standard antenna, and for the low gain problem, the power radiated to the wave absorbing material is sufficient, and the test distance between the antenna and the wall can be shortened to compensate the power. The relationship between gain and distance can be expressed by the Friis transmission formula as follows:

[0057]

[0058] P r : received power

[0059] P t : transmission power

[0060] G t : transmission antenna gain

[0061] G r : receiving antenna gain

[0062] λ: wavelength

[0063] d: distance between antennas

[0064] In PIM testing, the power radiated by the antenna is radiated into the anechoic chamber, and the PIM signal is generated including V PIM-ab and V PIM-sh The PIM signal is received by the receiving antenna. The receiving antenna and the transmitting antenna are independent, assuming G t =G r The return loss of the wave-absorbing material is taken into account.

[0065]

[0066] R ab : the reflection of the wave-absorbing material

[0067] When d is greater than the length of the wave-absorbing material, R ab can be assumed to be constant from different test angles. In dB units, then (2) becomes:

[0068] P r =P t +2G t -L+R ab (3)

[0069] The gain is expressed in dBi, and the power is expressed in dBm, L is the free space loss, which is often expressed as;

[0070]

[0071] c is the speed of light, and f is the speed of light.

[0072] 5. Grid division is adopted to ensure that the area of the large anechoic chamber wall radiation is sufficient.

[0073] The size of the anechoic chamber is large, and the area of a single antenna radiation is limited, so a suitable number of points need to be laid out to ensure that the test wall can be detected. In this method, based on the 3dB bandwidth of the antenna, the antenna radiation area is laid out with grid division to achieve full coverage.

[0074] The main coverage range of the standard antenna, θ h is the typical 3dB beamwidth angle. The horizontal coverage range of a single antenna is approximately as follows:

[0075] I h =2d x0 tan(θ h / 2) (5)

[0076] Similarly, the coverage range in the vertical direction is expressed as:

[0077] I v =2d x0 tan(θ v / 2) (6)

[0078] θ v :3dB beamwidth angle

[0079] The coverage of a standard antenna can be considered as a rectangle, and the area is I h ,I v This area is smaller than the coverage on the -x axis, so a single antenna cannot complete a good coverage test. The number of layout points required for horizontal and vertical direction tests is:

[0080]

[0081] I y :the length of the darkroom y direction.

[0082] I z :the length of the darkroom z direction.

[0083] The distance and calibration test position settings in the vertical and horizontal directions are: The number of test points increases with the test distance. Through such a layout and test, comprehensive coverage will be achieved along the -x axis. According to the test requirements, select the appropriate power spectral density and calculate the corresponding test point layout in the darkroom, and make the corresponding mark.

[0084] 6. Same test point deflection azimuth angle test.

[0085] Considering the directivity of the received PIM signal, a 60° position rotation is achieved by using the receiving and transmitting antennas at the same point. Within 60° of the azimuth angle, three directions are set, left, center and right, each with 60° to realize the deflection test, ensuring the same power positioning point, and realizing the coverage of the transmitting and receiving power in different directions.

[0086] 7. According to the above steps: select the method, system calibration, calculate the test position according to the power test, calculate the test layout point according to the antenna beam width, set the deflection test at the same point, and complete the test of different points in turn. Organize the data and issue the darkroom PIM performance test report.

[0087] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

[0088] The contents not described in detail in the specification of the present application are the known technology of those skilled in the art.

Claims

1. A large passive intermodulation darkroom test method, characterized by, The application relates to a passive intermodulation (PIM) test system and a test method thereof. A main radiation surface is determined according to the size of a darkroom and test index requirements and an installation position of the darkroom design, or a test target wall surface is selected according to customer requirements; A radiation type passive intermodulation test system is built; The radiation type passive intermodulation test system is calibrated; Test positions are calculated according to power test, test layout points are calculated according to antenna beam width, offset tests are arranged at the same point, and tests of different points are sequentially completed; The radiation type passive intermodulation test system comprises two signal source links, a frequency synthesizer, a duplexer, an antenna, a receiving link and a darkroom provided with a test target wall surface. Each signal source link comprises a signal source, a continuous wave amplifier and a directional coupler; the signal source is used for generating a test signal for testing; the continuous wave amplifier is used for amplifying the test signal; and the directional coupler is used for coupling a high-power signal on the link, and the coupled signal enters a power meter to monitor input power. The frequency synthesizer is used for synthesizing two amplified signals into one signal. The duplexer is a Tx / Rx duplexer, the Tx / Rx duplexer receives the signal synthesized by the frequency synthesizer, and sends the signal to the antenna through a Tx transmission channel; the transmitted power signal is radiated to the wall body, and the PIM signal generated by the wall body is received by the antenna and sent to the receiving link; The receiving link is used for receiving the PIM signal generated by the wall body and received by the antenna; The power signal transmitted by the signal source link enters the antenna, the antenna radiates the power signal to the wall surface of the darkroom, and the antenna receives the PIM signal generated by the wall surface; after receiving, the PIM signal is filtered through an Rx receiving filter to remove the transmission signal and noise signal, is amplified through a low-noise amplifier and is sent to a spectrum analyzer for observation; The bias value of the spectrum analyzer is determined by instrument measurement at a PIM test frequency point, which includes the low-noise amplifier gain and the insertion loss of the connecting cable and the receiving filter; A rated low-level signal is simulated by using a microwave signal source, is transmitted through the receiving link, and is received by the spectrum analyzer to calibrate the spectrum analyzer receiving bias value of the receiving link; The calibration of the radiation type passive intermodulation test system comprises the following steps: A flat metal aluminum plate is placed on the position of the metal mesh to simulate the full reflection state of ideal antenna radiation, and the test value is the test value of the test system itself; The test system is verified to have the ability to capture the PIM signal, and the test system is ensured to have normal test capability.

2. The method of claim 1, wherein, The antenna is a common antenna for radiation and transmission or double antennas for transmission and reception respectively.

3. The method of claim 1, wherein, The power meter is connected to the coupling end of the directional coupler to read the power level value at the entrance of the measured object; when the bias value of the power meter is calibrated, the attenuator and the probe are connected at the entrance of the antenna, and the bias value of the power meter is adjusted so that the reading of the power meter is consistent with the reading of the power meter connected with the probe.

4. The method of claim 1, wherein, The calibration of the radiation type passive intermodulation test system further comprises the following steps: a steel wire mesh of the same size is placed to test the generated PIM signal, and the test system is verified to have the ability to test the PIM signal.

5. The method of claim 1, wherein, According to the size of the main radiation surface of the darkroom, the antenna is placed at the geometric center of the darkroom, the radiation range and the radiation power spectral density are calculated according to the test antenna performance, and the distance is adjusted for testing.

6. The method of claim 1, wherein, According to the test requirements, the corresponding power spectral density is selected and the corresponding test point layout is calculated. The test target wall surface is divided into several grids, and each grid is tested respectively to realize the area coverage of the test target wall surface radiation.

7. The method of claim 1, wherein, Within the 60° azimuth angle, three directions are set, left, middle and right, each with 60° to realize the offset test, to ensure the same power positioning point and to realize the coverage of the transmission and reception power in different directions.

Images