Design And Implementation Of Horizontally Polarized Omnidirectional Calibration Antenna

Multiple probe antennas measurement system(MPAMS)utilizes multi-probe technology to provide a faster method for the electromagnetic field.Thus,in today's Over-the-air(OTA)measurements,MPAMS is widely used.However,due to the inconsistency of the absorbing materials,the inconsistency of the absorbing material combined with the different probe antennas,and the difference in gain of the different probes,MPAMS requires calibration to ensure the accuracy of the measurements.It's noted that the probe antenna is a dual-polarized antenna consist ing of vertical and horizonta l polarization,thus the calibration must be divided into these two polarizations.Since the horizontal polarization direction of each probe antenna is different,it is ideal to use a horizontally polarized(HP)omnidirectional antenna as a HP calibration antenna(CA).The gain variation of the CA determines the accuracy of the measurement.According to the CTIA,the gain ripple of the CAs for MPAMS must be less than 0.2 dB.In this paper,a HP omnidirectional antenna with small size,small ripple and low cross polarization is proposed for the application of HP calibration in MPAMS.The main works of this paper are:(1)The working and calibration principle of MPAMS are introduced,and the performances that HP omnidirectional antenna should meet are proposed.(2)Introducing the basic principle of antenna design,studying the design methods o f loop antenna,and simulat ing the HP omnidirectional antenna with HFSS.(3)The proposed antenna consists of the four arc-folded dipoles to achieve omnidirectional property.Then,adding parasitic strips icing on the cake,the antenna achieves small gain variation in horizontal plane no more than 0.16 dB as well as the 18% bandwidth(VSWR<2.0)from 2.25 GHz to 2.7 GHz.Besides,by using balun structures,the HP omnidirectional antenna has suppressed common-mode current on the coaxial cable and obtained a high cross-polarization ratio over than 24 dB.(4)Compare the difference between the measured results and the simulat ed results.Analyzing how the factors in the measurement system,such as the limited accurac y of the turntables,rotary axes etc.affect the performance of the HP omnidirectional antenna.