Research And Design On Several Key Technologies Of Antenna Measurement System

Antenna measurement is an important research direction in modern wireless technology.In this paper,the antenna measurement system is taken as the research object,starting from the difficulties in practical engineering design,the key components that affect the measurement performance of several antenna measurement systems are studied.Starting from the basic electromagnetic principle,the suppression of weak noise level is taken as the core,the system components with better performance are designed,so as to improve the overall performance of the system.The main innovative achievements of this paper are as follows:(1)The design of the calibration dipole of the multi-probe measurement system is studied.The traditional calibration dipole has the problems of narrow common-mode current suppression bandwidth and poor effect,which will bring greater uncertainty to the calibration of the measurement system.Based on the principle of antenna balance,this paper proposes a calibrated dipole with a voltage balun as the feed balance structure,which realizes the transition from parallel double lines to coaxial lines,and brings the feed through the shielded compact design.The asymmetry of the electromagnetic environment is minimized.The design method in this paper can make the calibration dipole achieve good common-mode current suppression effect within the relative bandwidth of more than 15%,and the measured antenna gain is about 2d Bi.The cross-polarization ratio of horizontal plane is greater than27 d B,and the gain change of horizontal plane is less than 0.2d B.Compared with the traditional calibration dipole,the dipole has the advantages of symmetrical vertical plane,small horizontal plane uncircularity,stable and reliable gain efficiency,etc.The high performance of the calibration dipole makes it suitable for the calibration of the gain and efficiency of the antenna measurement system,especially for improving the accuracy and reliability of the consistency calibration of the multi-probe measurement system.(2)The feed design of the compact antenna test range(CATR)is studied.The feed antenna of CATR is a key component that affects the performance of the quiet zone.The existing feed design pays more attention to the influence of the amplitude pattern and ignores the design of the antenna phase pattern,resulting in a quiet zone in the system.Problems such as low utilization rate and poor broadband phase characteristics.In this paper,an analysis method combining electromagnetics and optics is used to analyze the requirements of the phase pattern of the feed.A corrugated horn feed antenna with a stable phase center is designed for a millimeter-wave CATR.In this paper,the theoretical expression of the phase center of the horn is analyzed.The 45° plane phase center is used as the mixed phase center of the horn,and the phase center calculation is performed only once,which is faster and more convenient to optimize the phase performance.From the perspective of surface wave suppression,by adding a wave absorbing material to the edge of the outer surface of the horn,the irregular current on the outer surface of the horn is suppressed,so as to achieve a more stable phase center.The designed corrugated horn works in the 24-40 GHz frequency band and has the following performance: the phase center deviation of the working frequency band is less than ±0.25 mm,and the phase change within ±30°beam width is less than ±2.5°.Moreover,the measured return loss is less than-10 d B,the measured gain is 8-12 d Bi,and the measured cross-polarization level is less than-30 d B.The beam width of the whole frequency band is maintained at 56-70°,and the beam difference between different sections is less than5°.The achieved goals listed above make the proposed corrugated horn suitable for CATR requiring high-precision antenna measurements,and have been applied to actual industrial products.(3)The design method of a miniaturized passive intermodulation(PIM)chamber with low intermodulation was studied.In PIM measurement,the function of the anechoic chamber is to shield external electromagnetic signals,reduce reflections,and obtain accurate measurement results.However,due to the nonlinear characteristics of the absorbing material and the shielding enclosure,the chamber itself may introduce new PIM sources.The traditional method to reduce the influence of the chamber on the passive intermodulation measurement is to design a large-sized passive intermodulation test chamber to reduce the passive intermodulation level through the path loss.In this article,starting from the PIM generation mechanism,the source of the interference signal in the chamber is analyzed,and the absorbing material and shielding shell structure with extremely low PIM are designed to reduce the PIM level by suppressing the PIM level of the chamber itself instead of increasing the size.PIM noise brought by the dark room.According to the design principle of the chamber,the worst-case reflection level is analyzed,and the PIM level caused by the reflected signal is estimated,so as to determine the minimum chamber size design criterion that meets the design requirements.By comparing the low-PIM anechoic chamber proposed in this paper with the traditional PIM anechoic chamber,it shows the advantages of the low-PIM anechoic chamber and verifies the correctness of the theoretical analysis.Using this new design method can significantly reduce the size of the chamber(about one tenth of the traditional chamber)while ensuring the measurement accuracy,greatly reducing the construction cost,especially suitable for the production line PIM that requires small size and low cost Measurement.This work has been applied for IEEE international standard,which can be used as a guide for building a low PIM test environment.At the same time,this article also studied the evaluation methods of PIM chambers.Since the PIM measurement chamber itself may have the PIM noise level,when the antenna gain under test increases,the PIM noise level generated by the chamber will also increase.Therefore,it is necessary to define the maximum measurable gain of the PIM measurement chamber.However,high-gain antennas are usually difficult to achieve low PIM,and have narrow beamwidth and large volume.Thus,it is difficult to directly use for measurement.This article proposes a convenient approximation method to calculate the maximum measurable gain in an anechoic chamber.This method is achieved by using a low PIM medium gain directional antenna.By reducing the distance between the antenna and the chamber wall and reducing the path loss,the purpose of replacing the high-gain antenna with a medium-gain antenna is achieved.This article gives the specific relationship between distance and equivalent gain,and provides the measurement interval and measurement steps for scanning the entire chamber.The measurement method proposed in this paper can obtain the PIM noise floor of the chamber and the corresponding maximum measurable gain.The effectiveness and feasibility of this method are verified by measuring in two PIM measurement chambers with different performances.