Method for measuring surface accuracy of large reflector antenna at different elevation angles

Abstract

The application discloses a method for measuring surface accuracy of large reflector antenna at different elevations, and belongs to the technical field of large reflector antenna measurement. The method first measures the surface accuracy of the large reflector antenna at a working elevation by using a photogrammetry method, and takes the working elevation as a measurement reference of the surface accuracy at different elevations; then, the method uses a radio source method to measure noise power levels of the antenna aiming at a same radio source, a background cold space and a normal temperature load at the reference position and at different elevations by using a spectrum analyzer; since the gain deviation is caused by the different elevations of the antenna, the surface accuracy of the large reflector antenna at different elevations is obtained through a calculation formula. The method is simple and easy to implement, and has high popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of large reflector antenna measurement technology, and in particular to a method for measuring the surface accuracy of large reflector antennas at different elevation angles. This method is applicable to the measurement of the surface accuracy of large reflector antennas at different elevation angles in fields such as radio astronomy, deep space exploration, and satellite navigation. Background Technology

[0002] Surface accuracy is one of the important mechanical structural performance indicators of large reflector antennas, directly affecting electrical performance such as antenna gain, beamwidth, and sidelobes. Therefore, accurate measurement of the surface accuracy of large reflector antennas is crucial. Currently, common methods for measuring the surface accuracy of large reflector antennas include photogrammetry and microwave holography.

[0003] Photogrammetry, through multi-angle optical imaging and 3D reconstruction, obtains high-precision 3D coordinates of the antenna reflector structure and compares them with a theoretical parabolic model to obtain the antenna surface shape error. The core of microwave holography is to correlate the signals of a reference antenna and the antenna under test to obtain the far-field amplitude and phase distribution, then inversely deduce the aperture field amplitude and phase, and finally obtain the reflector shape deviation. These conventional methods for measuring the surface accuracy of large reflector antennas have certain limitations, specifically as follows:

[0004] 1. Photogrammetry: When measuring at different elevation angles, the workload is large, repeated measurements are required, the cycle is long, and the labor and time costs are high.

[0005] 2. Microwave holography: This method requires a reference antenna, and due to limitations in geographical location and satellite resources, it is difficult to achieve accurate surface measurements at different elevation angles.

[0006] 3. Difficulty in achieving dynamic measurement: Conventional measurement methods are aimed at the surface accuracy of the antenna when it is static, and cannot monitor the changes in the antenna's surface shape in real time when it is in operation (such as rotation or adjustment of elevation angle). Such dynamic deformation will directly affect the electrical performance of the antenna. Summary of the Invention

[0007] In view of this, the present invention proposes a method for measuring the surface accuracy of a large reflector antenna at different elevation angles. This method can measure the surface accuracy of a large reflector antenna at different elevation angles and has the characteristics of high measurement accuracy, simple operation, minimal environmental influence, short measurement cycle, and low cost.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for measuring the surface accuracy of a large reflector antenna at different elevation angles includes the following steps:

[0010] Step 1: Adjust the antenna to the reference position and use a spectrum analyzer to measure the maximum noise power level N of the radio source to which the antenna is pointed. star-r The noise power level N of the antenna pointing towards the background cold air. sky-r And the noise power level N when the input port of the low-noise amplifier is connected to a normal temperature load. load-r All units are dBm;

[0011] Step 2: Adjust the antenna to different elevation angles m, and use a spectrum analyzer to measure the maximum noise power level N of the antenna pointing at the radio source. star-m The noise power level N of the antenna pointing towards the background cold air. sky-m And the noise power level N when the input port of the low-noise amplifier is connected to a normal temperature load. load-m All units are dBm;

[0012] Step 3: Calculate the antenna's surface accuracy at different elevation angles using the following formula:

[0013]

[0014]

[0015] In the formula:

[0016] Noise temperature under normal load when the antenna is in the reference position, in K;

[0017] : Noise temperature of the low-noise amplifier at the reference position of the antenna, K;

[0018] : Noise temperature of the antenna under normal temperature load at an elevation angle of m, in K;

[0019] Noise temperature of the low-noise amplifier at an elevation angle m, in K;

[0020] ε r Surface accuracy of the antenna at the reference position, in cm;

[0021] ε m Surface accuracy of the antenna at an elevation angle of m, in cm;

[0022] : Gain difference of the antenna at the reference position and elevation angle m, in dB;

[0023] The elevation angle of the antenna at the reference position, in degrees;

[0024] : Angle of elevation (m), in degrees;

[0025] γ: Atmospheric attenuation at the zenith, in dB;

[0026] f: Operating frequency, GHz.

[0027] Furthermore, in step 1, the reference position is the working elevation angle of the antenna surface precision photogrammetry.

[0028] Furthermore, the noise power levels of the antenna directed at the radio source, the background cold air, and the normal temperature load were measured under clear, light wind, and cold air conditions.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. This method can measure the surface accuracy of large reflector antennas at different elevation angles. It features high measurement accuracy, simple operation, minimal environmental influence, short measurement cycle, and low cost.

[0031] 2. This method can realize dynamic measurement of the surface accuracy of large reflector antennas and monitor the surface shape changes of the antenna at different elevation angles in real time.

[0032] 3. This method is also applicable to the accuracy measurement of the reflector surface of medium and large antennas, and has good promotion and application value. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the principle of the present invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings.

[0035] A method for measuring the surface accuracy of a large reflector antenna at different elevation angles, comprising the following specific steps:

[0036] (1) Measure the noise power level of the large reflector antenna at the elevation reference position. The specific method is as follows:

[0037] Establish a test system, adjust the antenna to the reference position, and use a spectrum analyzer to measure the following:

[0038] The antenna is aligned with the maximum noise power level of the radio source, denoted by N. star-r This indicates that the unit is dBm;

[0039] The noise power level of the antenna pointing towards the background cold air is represented by N. sky-r This indicates that the unit is dBm;

[0040] The noise power level of the low-noise amplifier input port is connected to a room-temperature load, using N. load-r This indicates that the unit is dBm.

[0041] (2) Measure the noise power level of a large reflector antenna when it is pointed at the same radio source at different elevation angles. The specific method is as follows:

[0042] After completing the measurement in step 1, point the antenna at different elevation angles m and measure them using a spectrum analyzer:

[0043] With the antenna aligned with the maximum noise power level of the radio source at an elevation angle m, using N star-m This indicates that the unit is dBm;

[0044] The noise power level of the antenna pointing towards the background cold air is represented by N. sky-m This indicates that the unit is dBm;

[0045] The noise power level of the low-noise amplifier input port is connected to a room-temperature load, using N. load-m This indicates that the unit is dBm.

[0046] (3) Calculate the surface accuracy of the large reflector antenna at different elevation angles.

[0047] The surface accuracy of the antenna at its operating elevation angle has been obtained through photogrammetry. Since different antenna elevation angles will cause gain deviations, the surface accuracy of a large reflector antenna at different elevation angles can be calculated using the following formula:

[0048]

[0049]

[0050] In the formula:

[0051] : The maximum noise power level of the antenna aligned with the radio source at the reference position, in dBm;

[0052] : Noise power level of the antenna pointing towards the background cold air when the antenna is in the reference position, in dBm;

[0053] : Noise power level (dBm) of the low-noise amplifier connected to a normal-temperature load when the antenna is in the reference position;

[0054] Noise temperature under normal load when the antenna is in the reference position, in K;

[0055] Noise temperature of the low-noise amplifier, in Kelvin, when the antenna is in the reference position;

[0056] : The maximum noise power level of the antenna pointing directly at the radio source at an elevation angle of m, in dBm;

[0057] : Noise power level of the antenna pointing towards the background cold air at an elevation angle of m, in dBm;

[0058] The noise power (dBm) of the low-noise amplifier connected to a normal-temperature load at an elevation angle of m.

[0059] : Noise temperature of the antenna under normal temperature load at an elevation angle of m, in K;

[0060] Noise temperature of the low-noise amplifier at an elevation angle m, in K;

[0061] ε r Surface accuracy of the antenna at the reference position, in cm;

[0062] ε m Surface accuracy of the antenna at an elevation angle of m, in cm;

[0063] : Gain difference of the antenna at the reference position and elevation angle m, in dB;

[0064] : The elevation angle of the antenna at the reference position, in degrees (°);

[0065] :The elevation angle of the antenna at an elevation angle of m, in degrees "°";

[0066] γ: Atmospheric attenuation at the zenith, in dB;

[0067] f: Operating frequency, GHz.

[0068] In step (1), the surface accuracy of the large reflector antenna at the reference position is measured by photogrammetry. The reference position is the working elevation angle of the antenna photogrammetry.

[0069] In this method, the antenna must be pointed at the same radio source at the reference position and at different elevation angles. Atmospheric attenuation is a function of atmospheric temperature, humidity, pressure parameters, and the elevation angle of the antenna pointing at the radio source. The noise power levels of the radio source, the background cold air, and the ambient temperature load should be measured under clear, light wind, and cold air conditions.

[0070] Here is a more specific example:

[0071] A method for measuring the surface accuracy of a large reflector antenna at different elevation angles. (Refer to...) Figure 1The test system consists of a large reflector antenna, a low-noise amplifier, RF test cables, a servo controller, a room-temperature load, and a spectrum analyzer. The noise power level of the antenna is measured at a reference position and different elevation angles, with the antenna pointing at the same radio source, against a cold background, and under a room-temperature load. The surface accuracy of the large reflector antenna at different elevation angles is obtained through calculation formulas.

[0072] In this embodiment, the antenna under test is a Cassegrain dual-reflector antenna with an aperture of 30 meters and an operating frequency range of 9.4 GHz to 10 GHz. The surface accuracy of the photogrammetric antenna at the operating elevation angle is 0.0286 cm. The ground station antenna is located at 108.86°E, 30.82°N, the radio source is Cassiopeia (CasA), the orbit is provided by calibration software, the test frequency is 9.7 GHz, and the polarization is left-hand circular polarization.

[0073] The specific steps of this embodiment are as follows:

[0074] Step 1: When the antenna is at the elevation reference position, the elevation angle of the antenna is 46°. Point the antenna at the radio source and use a spectrum analyzer to measure the noise power levels of the antenna pointing at the radio source, the background cold air, and the normal temperature load when the antenna is at the reference position. The levels are -52.25 dBm, -54.82 dBm, and -45.95 dBm, respectively.

[0075] Step 2: When the antenna is at different elevation angles (m), and the elevation angle of the antenna is 23°, point the antenna at the radio source and use a spectrum analyzer to measure the noise power levels of the antenna pointing at the radio source, the background cold air, and the normal temperature load. The levels are -52.29 dBm, -54.64 dBm, and -45.96 dBm, respectively.

[0076] Step 3: Calculate the surface accuracy of the large reflector antenna at different elevation angles. At the reference position and elevation angle m, the ambient temperatures are 13°C and 11°C (286K and 284K respectively). The low-noise amplifier has a noise figure of 0.2, with noise temperatures of 13.48K and 13.38K respectively. The atmospheric attenuation at a frequency of 9.7GHz is 0.05 dB. Therefore, the surface accuracy of the antenna at elevation angle m is:

[0077]

[0078]

[0079] This invention employs the radio source method. First, photogrammetry is used to measure the surface accuracy of a large reflector antenna at its operating elevation angle, and this operating elevation angle is used as the measurement benchmark for surface accuracy at different elevation angles. Then, using the radio source method, a spectrum analyzer is used to measure the noise power level of the antenna pointing at the same radio source, against a cold background, and under a normal temperature load, at the benchmark position and at different elevation angles. Due to the gain deviation caused by different antenna elevation angles, the surface accuracy of the large reflector antenna at different elevation angles is finally obtained through calculation formulas. This invention can measure the surface accuracy of large reflector antennas at different elevation angles and features high measurement accuracy, simple operation, minimal environmental influence, short measurement cycle, and low operating cost.

Claims

1. A method for measuring the surface accuracy of a large reflector antenna at different elevation angles, characterized in that, Includes the following steps: Step 1: Adjust the antenna to the reference position and use a spectrum analyzer to measure the maximum noise power level N of the radio source to which the antenna is pointed. star-r The noise power level N of the antenna pointing towards the background cold air. sky-r And the noise power level N when the input port of the low-noise amplifier is connected to a normal temperature load. load-r All units are dBm; Step 2: Adjust the antenna to different elevation angles m, and use a spectrum analyzer to measure the maximum noise power level N of the antenna pointing at the radio source. star-m The noise power level N of the antenna pointing towards the background cold air. sky-m And the noise power level N when the input port of the low-noise amplifier is connected to a normal temperature load. load-m All units are dBm; Step 3: Calculate the antenna's surface accuracy at elevation angle m using the following formula: In the formula: Noise temperature under normal load when the antenna is in the reference position, in K; : Noise temperature of the low-noise amplifier at the reference position of the antenna, K; : Noise temperature of the antenna under normal temperature load at an elevation angle of m, in K; Noise temperature of the low-noise amplifier at an elevation angle m, in K; ε r Surface accuracy of the antenna at the reference position, in cm; ε m Surface accuracy of the antenna at an elevation angle of m, in cm; : Gain difference of the antenna at the reference position and elevation angle m, in dB; The elevation angle of the antenna at the reference position, in degrees; : Angle of elevation (m), in degrees; γ: Atmospheric attenuation at the zenith, in dB; f: Operating frequency, GHz.

2. The method for measuring the surface accuracy of a large reflector antenna at different elevation angles according to claim 1, characterized in that, In step 1, the reference position is the working elevation angle of the antenna surface precision photogrammetry.

3. The method for measuring the surface accuracy of a large reflector antenna at different elevation angles according to claim 1, characterized in that, The noise power levels of the antenna directed at the radio source, background cold air, and normal temperature load were measured under clear, light wind, and cold air conditions.

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