Multi-copter unmanned aerial vehicle based antenna far field pattern near range measurement system and method

Abstract

The application relates to a kind of multi-rotor unmanned aerial vehicle-based antenna far field pattern near distance measurement system and method, including multi-rotor unmanned aerial vehicle, signal transceiver unit, data acquisition equipment, photoelectric converter;Signal transceiver unit includes signal transceiver module, electro-optical converter, receiving antenna and wireless transmission module;The application is centered on the antenna to be measured, controls multi-rotor unmanned aerial vehicle to carry out horizontal semicircle flight around the antenna to be measured, and signal transceiver module emits an electric signal every N degrees on azimuth angle θ;Electric signal is converted into optical signal, is transmitted to photoelectric converter through optical fiber and is converted into electric signal again and is emitted through the antenna to be measured, and receiving antenna receives the electric signal, carries out near far field conversion processing, obtains the far field pattern of the antenna to be measured.The application can obtain the accurate amplitude and phase information of the antenna to be measured because the signal received by receiving antenna and the transmitting signal have the same source, form coherence.

Description

Technical Field

[0001] This invention belongs to the field of antenna measurement, specifically relating to a system and method for acquiring the far-field radiation pattern of an antenna. Background Technology

[0002] Antenna measurements typically require meeting far-field conditions, meaning the test distance needs to be greater than 2D. 2 / λ, where D is the maximum size of the antenna and λ is the operating frequency. When the antenna under test is large or operates at a high frequency, the measurement using a multi-rotor UAV is limited by payload weight and airspace constraints, often making it difficult to meet far-field conditions. Therefore, it is necessary to perform measurements at close range to obtain the amplitude and phase information of the signal, and then use a near-far field transform algorithm to obtain the far-field radiation pattern of the antenna under test. The paper "Dual-ProbeNear-Field Phaseless Antenna Measurement System on Board a UAV, Sensors, 2019, 19, 4663" provides a method for obtaining the far-field radiation pattern of an antenna using a multi-rotor UAV for close-range measurement. This method uses a UAV carrying a signal receiving module to fly close to the antenna under test along a planned path. The signal receiving module obtains the amplitude information of the transmitted signal from the antenna under test at two different locations. Using these two amplitude information, the phase information of the received signal at these two locations is estimated, and the far-field radiation pattern of the antenna is obtained through Fourier transform. The method described in the literature mainly uses optical phase restoration theory, combined with an iterative Fourier transform algorithm to restore the phase of the received signal at the location. However, the choice of the initial iteration phase has a significant impact on the accuracy and convergence of phase reconstruction, making it difficult to obtain accurate phase information, which in turn seriously affects the measurement accuracy of the antenna's far-field radiation pattern. Summary of the Invention

[0003] The purpose of this invention is to provide a near-range measurement system and method for antenna far-field radiation patterns based on multi-rotor UAVs, which solves the technical problem of poor measurement accuracy caused by inaccurate phase reconstruction of amplitude information from signals received at two different locations in the prior art.

[0004] The technical solution of this invention is:

[0005] A near-field measurement system for antenna far-field radiation patterns based on a multi-rotor UAV is characterized by comprising a multi-rotor UAV 6, a signal transceiver unit mounted on the multi-rotor UAV 6, a data acquisition device 9, and an optoelectronic converter 2 located on the ground and connected to the antenna under test 1. The signal transceiver unit includes a signal transceiver module 7, an electro-optical converter 5, a receiving antenna 8, and a wireless transmission module. The electro-optical converter 5 converts the electrical signal transmitted by the signal transceiver module 7 into an optical signal and transmits it to the optoelectronic converter 2 via an optical fiber 4. The optoelectronic converter 2 converts the received optical signal into an electrical signal and inputs it to the antenna under test 1 for transmission. The receiving antenna 8 receives the electrical signal transmitted by the antenna under test 1 and sends it to the signal transceiver module 7. The wireless transmission module transmits the electrical signal transmitted and received by the signal transceiver module 7 to the data acquisition device 9. The data acquisition device 9 performs near-field and far-field transformation based on the electrical signal transmitted and received by the signal transceiver module 7 to obtain the far-field radiation pattern of the antenna under test 1.

[0006] When the received signal is weak, the above measurement system may also include a power amplifier disposed between the photoelectric converter 2 and the antenna under test 1.

[0007] The signal transmitting module 7 is preferably a P440 module capable of transmitting and receiving ultra-wideband time-domain signals; the receiving antenna 8 is preferably a small microstrip log-periodic antenna; the transmitting end of the P440 module is connected to the electro-optic converter 2 via a microwave cable.

[0008] The aforementioned miniature microstrip log-periodic antenna has the same height and polarization as the antenna under test 1; the aforementioned optical fiber 4 has a length greater than... Where D is the aperture of the antenna under test, and λ is the operating wavelength of the antenna under test.

[0009] The aforementioned data acquisition device 9 is preferably installed in the UAV ground station; the aforementioned wireless transmission module transmits the electrical signals transmitted and received by the signal transceiver module 7 to the data acquisition device 9 wirelessly.

[0010] The near-range measurement method for the far-field radiation pattern of the antenna in the system described in this invention includes the following steps:

[0011] 1) With the antenna under test as the center, control the multi-rotor UAV to fly horizontally in a semi-circular motion around the antenna under test; during the flight, the signal transceiver module transmits an electrical signal and receives a corresponding near-field data every N degrees at the azimuth angle θ.

[0012] The specific steps for the signal transceiver module to transmit an electrical signal and receive corresponding near-field data are as follows:

[0013] 1.1) The transmitter of the signal transceiver module on the multi-rotor UAV converts the transmitted electrical signal into an optical signal through an electro-optic converter;

[0014] 1.2) The optical signal is transmitted through optical fiber to a photoelectric converter and then converted into an electrical signal;

[0015] 1.3) The antenna under test transmits the converted electrical signal to the receiving antenna on the multi-rotor UAV, which then enters the receiving end of the signal transceiver module as near-field data;

[0016] 2) Perform near-field to far-field transformation on the near-field data; the formula for the near-field to far-field transformation is as follows:

[0017] E(R,θ)=E(r,θ)*W(θ)

[0018] in:

[0019] E(r,θ) represents the near-field data of the antenna under test at different angles before transformation;

[0020] E(R,θ) represents the transformed far-field data of the antenna under test at different angles;

[0021] r represents the near-field distance;

[0022] R represents the far-field distance;

[0023] W(θ) is a convolution function that varies with angle.

[0024] When the far-field distance is R, W(θ) is expressed as:

[0025]

[0026] Where ω(n) is the spectral component of the far-field mode. Spectral components of the near-field mode The ratio of .

[0027] When the far-field distance is infinite, W(θ) can be expressed as:

[0028]

[0029] in: n represents the cutoff number, which is |n|≤N0, N0≥kD+10, where D is the minimum sphere radius surrounding the target, k is 2π / λ, and λ is the wavelength.

[0030] Ideally, the aforementioned signal transceiver module should transmit an electrical signal and receive a corresponding near-field data every 1 degree of azimuth angle θ.

[0031] The beneficial effects of this invention are:

[0032] This invention utilizes a multi-rotor UAV equipped with modules for transmitting and receiving signals. An electro-optical converter converts the transmitted signal into an optical signal, which is then transmitted via optical fiber to the antenna under test. A photoelectric converter then converts the optical signal back into an electrical signal, which is transmitted by the antenna under test and finally received by the module on the UAV, completing signal acquisition. Because the signal received by the small airborne antenna shares the same source as the transmitted signal, forming coherence, this method can obtain accurate amplitude and phase information of the antenna under test. Based on this, a near-field to far-field transformation can be performed to obtain a high-precision far-field radiation pattern of the antenna under test. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the near-range measurement system for the far-field radiation pattern of an antenna based on a multi-rotor UAV, as described in this invention.

[0034] Figure 2 This is a graph of the near-field amplitude data of the antenna under test in the measurement method of this invention;

[0035] Figure 3 This is a graph of the near-field phase data of the antenna under test in the measurement method of this invention;

[0036] Figure 4 This is a comparative schematic diagram of the near-field measurement results, extrapolated far-field results, and far-field measurement results of the antenna under test in the measurement method of this invention.

[0037] Figure reference numerals: 1-Antenna under test; 2-Electro-optical converter; 3-Antenna bracket; 4-Fiber optic cable; 5-Electro-optical converter; 6-Multi-rotor UAV; 7-Signal transceiver module; 8-Receiving antenna; 9-Data acquisition equipment. Detailed Implementation

[0038] The working principle of this invention is as follows: This invention utilizes a near-range measurement system for the far-field radiation pattern of an antenna based on a multi-rotor UAV. A module capable of transmitting and receiving signals is mounted on the multi-rotor UAV. The receiving end of the module is connected to a small receiving antenna within the transmission frequency range. The transmitting end of the module is connected to an electro-optical converter, which converts the transmitted electrical signal into an optical signal. The converted optical signal is transmitted through optical fiber to the antenna under test (DUT), where a photoelectric conversion module converts the transmitted optical signal back into an electrical signal and inputs it to the DUT. When the received signal is weak, a power amplifier is added between the photoelectric converter and the DUT to increase the signal strength input to the DUT. The module is powered by the power supply on the UAV and continuously transmits signals. The transmitted signal is ultimately transmitted by the DUT and received by the antenna on the module. Since the signal transmitted by the DUT and the signal transmitted by the module are the same signal, the received signal contains both amplitude and phase information.

[0039] This invention utilizes a near-range measurement system for the far-field radiation pattern of an antenna based on a multi-rotor UAV. (See details below.) Figure 1 A ranging and communication module P440 (signal transceiver module 7), capable of transmitting and receiving ultra-wideband time-domain signals, a small microstrip log-periodic antenna (receiving antenna 8), and an electro-optical converter 5 are mounted on a quadcopter UAV (multi-rotor UAV 6). The P440 module operates in the 3.1 GHz to 4.8 GHz frequency band, the small microstrip log-periodic antenna can transmit or receive signals from 1 GHz to 6 GHz, and the electro-optical converter 5 has a maximum operating frequency of 6 GHz. The antenna under test 1 is a standard gain horn antenna BJ40 with a maximum aperture of approximately 0.6 meters and an operating frequency of 3.2 GHz to 4.9 GHz. The antenna under test 1 is supported on an antenna bracket 3 at a height of 1.5 meters and is horizontally polarized. The airborne small microstrip log-periodic antenna is at the same height as the antenna under test 1 and has the same polarization. The transmitter of the P440 module is connected to the electro-optical converter 5 via a short microwave cable, which converts the transmitted electrical signal into an optical signal. The converted optical signal is then transmitted through optical fiber 4 to the antenna under test 1. A photoelectric converter 2, with a maximum operating frequency of 6 GHz, converts the optical signal back into an electrical signal, which is then input to the antenna under test 1 and transmitted. The transmitted signal propagates through space and is received by a small microstrip log-periodic antenna on the airborne end, entering the receiver of the P440 module. Since the received signal shares the same source as the transmitted signal, it is coherent and contains both amplitude and phase information. The data acquisition device 9 performs near-field and far-field transformations based on the electrical signals from the P440 module and the received electrical signals to obtain the far-field radiation pattern of the antenna under test 1.

[0040] The principle of this invention, which utilizes a multi-rotor UAV to acquire the far-field radiation pattern of an antenna at close range, is as follows: Since the antenna under test is stationary, it is necessary to control the UAV to fly around the antenna to collect data. Firstly, to ensure that measurements are performed in the near-field radiation region of the antenna under test, the test distance needs to be greater than [missing information]. Where D is the antenna aperture and λ is the operating wavelength. Next, with the antenna under test as the center, the starting position of the multi-rotor UAV's flight is set, and the flight distance is calculated based on the starting position. Then, based on the minimum sampling time of the signal transceiver module and the required number of sampling points, the required flight time of the multi-rotor UAV is obtained. Finally, the flight speed of the multi-rotor UAV is calculated based on the flight distance and flight time. Measuring these parameters yields the near-field data E(r,θ) of the antenna under test at different angles.

[0041] To obtain the far-field radiation pattern of the antenna under test, a near-field transformation needs to be performed on the acquired near-field data. The formula for the near-field transformation is as follows:

[0042] E(R,θ)=E(r,θ)*W(θ) (1)

[0043] Where E(r,θ) represents the near-field data before transformation, and E(R,θ) represents the far-field data after transformation. r represents the near-field distance, and R represents the far-field distance. W(θ) is a convolution function that varies with angle, which can be expressed as:

[0044]

[0045] Where ω(n) is the ratio of the spectral components of the far-field mode to the near-field mode:

[0046]

[0047] When the far-field distance is infinite, since the Hankel function is zero for any infinite mass of any order, the convolution function is:

[0048]

[0049] in:

[0050]

[0051] n represents the cutoff number, which is generally taken as |n|≤N0, N0≥kD+10, where D is the minimum sphere radius surrounding the target, k is 2π / λ, and λ is the wavelength.

[0052] The specific testing process of this invention, which utilizes a multi-rotor UAV to acquire the far-field radiation pattern of an antenna at close range, is as follows: Centered on the antenna under test, the UAV is controlled to rotate around it, measuring the near-field data. First, based on the formula for the near-field radiation zone, with a center frequency of 4 GHz, the maximum aperture of the antenna under test is 0.6 meters. Therefore, to meet the near-field radiation zone requirements, the distance between the two is 1 meter, meaning the UAV's flight radius is 1 meter. Taking the normal direction perpendicular to the aperture plane of the antenna under test as the azimuth angle of 0 degrees, the UAV flies clockwise from the left end (-90 degrees) to the right end (90 degrees). Based on the UAV's flight radius, the flight path is calculated to be 3.14 meters. The sampling interval of the signal transceiver module is set to collect 10 data points per second. From the azimuth angle of -90 degrees to 90 degrees, 181 data points need to be collected, resulting in a sampling time of 18 seconds. Therefore, the UAV's flight speed is 0.17 meters per second. After determining these parameters, the drone's flight path was set to a horizontal semicircle. Once the drone reached its starting position, the P440 module began collecting data. Based on the calculated flight speed, the P440 module completed data acquisition after the drone reached its destination, obtaining the amplitude and phase of the near-field of the antenna under test. Figure 2 and Figure 3 As shown.

[0053] from Figure 2 As can be seen, the amplitude data of the antenna under test is slightly distorted due to the failure to meet the far-field test conditions. The phase conforms to the phase distribution law of a horn antenna, but a dip appears near the center position. Therefore, it is necessary to further obtain the far-field radiation pattern of the antenna under test through near-field transformation.

[0054] First, the amplitude and phase data of the near field of the antenna under test acquired by the P440 module are smoothed. Then, the measured near field data E(r,θ) is processed using formula (1). 181 Perform a near-field to far-field transformation to obtain the extrapolated far-field radiation pattern:

[0055] E(R,θ 181 )=E(r,θ 181 )*W(θ 181 (5)

[0056] Where E(r,θ) 181 E(R,θ) represents the near-field data before extrapolation. 181 The ) represents the extrapolated far-field data. The near-field distance r is 1m, the far-field distance R is 100m, and the cutoff number is 140.

[0057] The near-field measurement results, extrapolated far-field results, and far-field measurement results of the antenna under test are as follows: Figure 4 As shown in the figure, there is a significant difference between the near-field measurement results and the far-field measurement results of the antenna under test. However, after near-field and far-field transformation processing, the extrapolated far-field radiation pattern matches well with the measured far-field radiation pattern, demonstrating the effectiveness of the phase acquisition and near-field and far-field transformation methods.

Claims

1. A near-range measurement system for far-field radiation patterns of an antenna based on a multi-rotor unmanned aerial vehicle (UAV), characterized in that: Includes a multi-rotor drone (6), a signal transceiver unit mounted on the multi-rotor drone (6), a data acquisition device (9), and an optoelectronic converter (2) set on the ground and connected to the antenna under test (1); The signal transceiver unit includes a signal transceiver module (7), an electro-optic converter (5), a receiving antenna (8), and a wireless transmission module; The electro-optic converter (5) converts the electrical signal emitted by the signal transceiver module (7) into an optical signal and transmits it to the photoelectric converter (2) through the optical fiber (4); The photoelectric converter (2) converts the received optical signal into an electrical signal and inputs it to the antenna under test (1) for transmission; The receiving antenna (8) receives the electrical signal transmitted by the antenna under test (1) and sends it to the signal transceiver module (7); The wireless transmission module transmits the electrical signals transmitted and received by the signal transceiver module (7) to the data acquisition device (9); The data acquisition device (9) performs near-field and far-field transformation based on the electrical signals transmitted and received by the signal transceiver module (7) to obtain the far-field radiation pattern of the antenna under test (1).

2. The antenna far-field pattern short-range measurement system based on a multi-rotor UAV according to claim 1, characterized in that: It also includes a power amplifier disposed between the photoelectric converter (2) and the antenna under test (1).

3. The near-range measurement system for far-field radiation pattern of an antenna based on a multi-rotor UAV according to claim 1 or 2, characterized in that: The signal transceiver module (7) is a P440 module capable of transmitting and receiving ultra-wideband time-domain signals; The receiving antenna (8) is a small microstrip log-periodic antenna; The transmitter of the P440 module is connected to the photoelectric converter (2) via a microwave cable.

4. The antenna far-field pattern short-range measurement system based on a multi-rotor UAV according to claim 3, characterized in that: The small microstrip log-periodic antenna is at the same height as the antenna under test (1) and has the same polarization. The length of the optical fiber (4) is greater than Where D is the aperture of the antenna under test (1) and λ is the operating wavelength of the antenna under test (1).

5. The antenna far-field pattern short-range measurement system based on a multi-rotor UAV according to claim 4, characterized in that: The data acquisition device (9) is installed in the UAV ground station; the wireless transmission module transmits the electrical signals emitted and received by the signal transceiver module (7) to the data acquisition device (9) wirelessly.

6. A method for near-range measurement of the far-field radiation pattern of an antenna based on the system described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) With the antenna under test as the center, control the multi-rotor UAV to fly horizontally in a semi-circular motion around the antenna under test; during the flight, the signal transceiver module transmits an electrical signal and receives a corresponding near-field data every N degrees at the azimuth angle θ. The specific steps for the signal transceiver module to transmit an electrical signal and receive corresponding near-field data are as follows: 1.1) The transmitter of the signal transceiver module on the multi-rotor UAV converts the transmitted electrical signal into an optical signal through an electro-optic converter; 1.2) The optical signal is transmitted through optical fiber to a photoelectric converter and then converted into an electrical signal; 1.3) The antenna under test transmits the converted electrical signal to the receiving antenna on the multi-rotor UAV, which then enters the receiving end of the signal transceiver module as near-field data; 2) Perform near-field to far-field transformation on the near-field data; the formula for the near-field to far-field transformation is as follows: E(R,θ)=E(r,θ)*W(θ) in: E(r,θ) represents the near-field data of the antenna under test at different angles before transformation; E(R,θ) represents the transformed far-field data of the antenna under test at different angles; r represents the near-field distance; R represents the far-field distance; W(θ) is a convolution function that varies with angle.

7. The method for near-range measurement of antenna far-field radiation pattern according to claim 6, characterized in that: When the far-field distance is R, W(θ) is expressed as: Where ω(n) is the spectral component of the far-field mode. Spectral components of near-field mode The ratio of .

8. The method for near-range measurement of antenna far-field radiation pattern according to claim 6, characterized in that: When the far-field distance is infinite, W(θ) can be expressed as: in: n represents the cutoff number, which is |n|≤N0, N0≥kD+10, where D is the minimum sphere radius surrounding the target, k is 2π / λ, and λ is the wavelength.

9. The method for near-range measurement of antenna far-field radiation pattern according to claim 6, 7, or 8, characterized in that: The N=1.

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