共模电流对多探头天线测量系统影响的研究

Research on common mode current aspect of multi-probe antenna measurement system

校准天线作为校准系统的主力部件,其性能直接决定了测量系统的精确度。对于未设计扼流结构的校准天线,天线上的部分电流会流到与其连接的线缆的外表面,线缆外表面的这种电流也称为共模电流。共模电流会改变校准天线的辐射性能,给系统的增益、效率等校准均不确定的误差。针对上述问题,研究和定量分析了与校准天线连接的线缆上存在的共模电流会给多探头天线测量系统的校准带来的误差,并根据仿真结果,提出了校准环天线在设计时应该满足大于25 dB的交叉极化比指标。然后通过两个校准环天线的实例,介绍了如何设计巴伦结构让环天线在宽带宽内实现抑制共模电流的效果。最后,通过对交叉极化比大于25 dB的环天线进行测量,验证了其抑制共模电流的效果,并根据其实测的交叉极化比与环向增益纹波,验证了交叉极化比对环天线环向增益纹波的影响,对多探头天线测量系统的高精度测量有着重要意义。

The calibration antenna is the main component of the calibration system.Its performance directly determines the accuracy of the measurement system.If the calibration antenna is lack of impressing current structure,the degree of imbalance is introduced between the feeding coaxial cable and the calibration antenna.A part of the current on the antenna will flow on the outer surface of the transmission cable,which is known as a common-mode current.The common-mode current has influence on the radiation performance of the calibrated antenna.It can also bring uncertain error to the calibrated gain and efficiency.First,we study and analyze the errors that the common-mode current would bring to calibration of the multi-probe antenna measurement system.Based on the simulation results,we propose that the calibration loop antenna should meet the cross-polarization ratio larger than 25 dB.Then,through the design examples of two calibrated loop antennas,we introduce how to design the balun structure to effectively suppress the common mode current in a wide bandwidth.Finally,we measure the calibration loop antenna with a cross-polarization ratio larger than 25 dB to evaluate its effectiveness in suppressing common-mode currents.Based on the measured cross-polarization ratio and gain ripple,we verify the effectiveness of the cross-polarization ratio on the gain ripple of the loop antenna.Therefore,it is of great significance to the high accuracy of measurements in multiple probe antennas measurement system.