Research On Design Of Circularly Polarized Antenna Based On Characteristic Mode Theory

Circularly polarized(CP)antennas are widely used in global positioning system(GPS),mobile satellite,radio frequency identification(RFID)and other fields due to their unique advantages in multipath distortion and polarization mismatch.Characteristic mode theory has a clear physical concept and plays an increasingly important role in antenna design.Based on the orthogonality of characteristic mode,circular polarization antenna is studied in this paper.The main contents and innovations are as follows:1.An single feed circularly polarized loop antenna is proposed.In this paper,a pair of 3.5nH inductors is introduced to split a pair of degenerate modes,and microstrip line feed-side was adopted to stimulate the splitted degenerate modes to generate circular polarization.Two resonant points appear in the impedance matching because of the two modes,which expands the impedance bandwidth,and the meatured impedance bandwidth reaches 47%.The measured 3dB axial ratio bandwidth reaches 8.3%and the measured maximum gain is 6.2dBic.The antenna works in the 2.4GHz band and can be used for local area network wireless LAN communication.2.A polarization reconfigurable and frequency reconfigurable loop antenna is proposed.In this paper,two pairs of parallel inductors,capacitors and four PIN diodes are loaded on the loop antenna.The four diodes have four working states,which control the loading state of inductors and capacitors.The characteristic modes of the loop antenna are different under different loading states.Different polarizations are realized in four operating bands:left-hand circular polarization at 2.4GHz with maximum gain of 6.2dBic,right-hand circular polarization at 2.85GHz with maximum gain of 7.8dBic,45° linear polarization at 2.7GHz with maximum gain of 8.2dB,0° linear polarization at 4.5GHz with maximum gain of 8.7dB.3.A multi-band high-gain circularly polarized antenna for 6G applications is proposed.The antenna also supports 2.4GHz,3.5GHz,5.3GHz and 5.8GHz bands.Finally,2.27-2.5GHz left-hand circular polarization,3.28-3.7GHz left-hand circular polarization,5.44-5.81 GHz right-hand circular polarization,6.42-7GHz right-hand circular polarization are achieved.In frequency bands 2.35-4.07GHz and 5.018GHz,53.6%and 46%of matching bandwidth are achieved,at frequency bands 2.27-2.5GHz,3.28-3.7GHz,5.44-5.81GHz and 6.42-7GHz,the maximum gain is up to 10dBic with 9.6%,12%,6.6%and 8.6%axial bandwidth respectively.