Design Of A High Performance Dual-Polarized Probe For Near Field Measurement

As a key component of the wireless communication system,the antenna plays an indispensable role.Antenna measurement is an important method for comprehensive evaluation of antenna performance,which runs through the research,production,commissioning and delivery of antennas.In order to cope with the rapid development of modern communication systems,antenna measurement technology is constantly improving.Antenna near-field measurement is widely recognized for its high efficiency and high accuracy.New technologies in the field of antenna near-field measurement place higher demands on the measurement probes.It is hoped that the probes will have the characteristics of ultra-wideband,dual polarization,and high cross-polarization isolation.This thesis designs a high-performance dual-polarization probe for antenna near-field measurement,which mainly includes the following tasks: 1.An improved design of a single-layer copper-clad Vivaldi antenna.The original antenna has the problems of excessive low-band VSWR,poor cross-polarization isolation,and poor symmetry of the mid-to-high frequency band pattern.The single-layer copper-clad Vivaldi antenna model was improved,and a double-layer copper-clad Vivaldi antenna was designed.The improved antenna adopts upper,middle and lower three-layer design,the middle layer is the dielectric substrate,and the upper and lower layers are metal-clad copper.The antenna adopts CPW-stripline coupling feed structure,and uses port branch matching resistance to improve the VSWR of the antenna.However,the problems of crosspolarization isolation does not meet the index and the symmetry of the pattern is still poor.2.A high-performance dual-polarized Vivaldi antenna with a double-feed point structure used as a near-field measurement probe is designed.The two sets of improved antennas are connected in parallel in a horizontal row,and the strip line T-shaped power splitter is used to distribute the antenna port energy to the two feeding points evenly,ensuring that the amplitude and phase of the dual-polarization probe are consistent at different polarizations.Providing metal vias around the feeder improves the symmetry of the probe pattern.The antenna is slotted to further improve the symmetry of the pattern and the low-band VSWR.The technical specifications of the designed probe are as follows: VSWR in the operating frequency band is less than 2,cross-polarization isolation is greater than 30 d B,and dual-port isolation is greater than 60 dB.3.The dual-polarized Vivaldi probe was processed and tested in the microwave dark room of Xidian University.During the test,the effect of improving the pattern of the specific position of the probe designed by wrapping different sizes of absorbing materials was tested and verified.The test results agree well with the simulation results.The designed probe has been used in a cylindrical near-field measurement system.