Design And Implementation Of Low-profile Circularly Polarized Antenna And Dual-frequency Circularly Polarized Antenna

In recent years,more and more attention have been paid to the artificial magnetic conductors(AMC),utilizing which the profile of circularly polarized antennas can be reduced.At the same time,the printed monopole is often used as a type of antenna to realize a dual-band circularly polarized performance for its advantages such as simple structure,easy processing,low cost.Thus,it becomes another research hotspot in the field of circular polarized antennas.Therefore,based on the two hotspots,this paper is manly focused on the design of circularly polarized antennas to achieve the demand characteristics,for instance low-profile and dual band.For the low profile design of the antenna,a parallel symmetrical dipole circular polarization antenna based on AMC has been proposed in this paper.The antenna consists of a radiating element,an AMC unit,and a feeding network.And,when the PEC and AMC are used as antenna reflectors respectively,the performances at different situations are compared.The results show that the antenna's profile can be reduced to 0.066 ?0 with the AMC.Meanwhile,the bandwidth of the antenna Axis ratio less than 3 dB is 150 MHz(2.34-2.49GHz).And.in this bandwidth,the antenna's reflection parameter(S11)is less than-10 dB.Then,for the requirement of the dual band performance,a dual-frequency circularly polarized monopole antenna has been designed and manufactured,which can simultaneously cover 5.2/5.8GHz-WLAN.2.5/3.4GHz-WiMAX and 5.5GHz-WiFi bands.This antenna is fed by a microstrip line,its constituent parts--the L and E monopoles can generate the low-frequency circularly polarized radiation,and the asymmetrical alike Yagi-Uda comes into high-frequency circularly polarized radiation.Through the above description,this antenna can achieve the dual-band circular polarization characteristic.The measured results show that the bandwidth of the antenna S11(less than-10dB)are 1.75GHz(2.50-4.25GHz)and 1.51 GHz(4.39-5.90GHz).The bandwidths with the axis ratio less than 3dB are 1.08GHz(2.41-3.49GHz)and 0.69GHz(5.02-5.71 GHz),respectively.And,the average gain in thees bands reaches 2.5dBi.Finally,by the precious analysis of the two antenna gains,their gains are stable and have a good circular polarization radiation characteristic.