Research On Open-Ended-Waveguide Probe Antenna For Planar Near-field Measurement

The Open-Ended-Waveguide(OEW)have simple structures,symmetrical shapes,and superior pattern characteristics.They are often used as measurement probes in Near-Field antenna measurement systems.Modern high-precision measurement systems have high requirements on the bandwidth,polarization purity,pattern,and isolation of the probe.The rectangular OEW is the most common type of probe in near-field measurement,known for their wide beamwidth and small aperture.There are also disadvantages such as narrow bandwidth,poor port matching,and single-polarization capabilities.In view of the above issues,this thesis mainly studies dual-polarized,wideband,high-polarity purity,and highisolation OEW,which are used as measurement probes for high-precision measurement systems.This thesis designs a high performance OEW antenna based on a circular OEW.First,an exponential reverse ridged circular OEW antenna is proposed.Based on the basic theoretical knowledge of the ridged waveguide,the design principle and optimal size of the ridged waveguide are analyzed,and the bandwidth of the OEW antenna is expanded by a special four-ridged structure.Two pairs of differential co-axial probes excite two polarization modes.This part analyzes the influence of the multilayer axial corrugated structure on the radiation performance of the antenna.The gain and the stability of the pattern in the frequency band are improved by the multilayer corrugated structure.Simulation results show that the designed antenna operates in the band of 5.7GHz-12.3GHz frequency.The qualified Voltage Stangding Wave Ratio(VSWR)of two ports is achieved.Polarization purity and port isolation are greater than 40 d B.The gain is from 7.5dBi to 9dBi.Beam width of the pattern is from 60 � to 90 �.Secondly,a small aperture circular OEW antenna with a special ridge line is designed.Based on the design of the exponential reverse ridge circular OEW antenna,the ridge curve and ridge structure are optimized.The ridge structure is improved and the cutoff frequency is reduced.A single-layer corrugated structure is used to achieve the requirements of small aperture and low scattering of the probe antenna.A wideband power divider with differential output is designed to feed the small aperture circular OEW antenna.This design antenna works in the frequency band of 5.89GHz-12 GHz,the VSWR is less than 2,the port size is small,the polarization purity and port isolation are more than 40 d B,the gain is between 6.8dBi-10 dBi,and the pattern beam width is between 50 � to 90 �.In the Planar Near-Field measurement of the antenna,the radiation of the probe antenna will affect the measurement results of the antenna under test(AUT),and probe compensation is necessary for near-field measurement.Considering the above designed circular-opened waveguide probe antenna,the thesis analyzes the theoretical basis of near-far field transformation including probe compensation and uses corresponding MATLAB programs with a computer to compensate the designed broadband dual-polarization measurement probe.The effectiveness of the probe compensation algorithm is verified by using simulation data and measured data.Thus that designed probe can be better used in planar Near-Field measurement systems.