Study Of Circularly Polarized Antenna Based On Phase Control Theory

With the development of modern communication technology,more requirements for circularly polarized antennas are provided by communication system.However,most of the circularly polarized antennas control phase only to achieve ideal circularly polarized performance,which is difficult to meet the growing demand of modern communication system.Here,the circularly polarized microstrip antennas based on the theory of phase control are investigated in depth,so as to meet different requirements for changeful communication environment.The main work and innovative achievements are as follows:1.Circularly-polarized filtering antenna based on phase control theory:① The novel method of circularly polarized filtering antenna is proposed based on the phase control theory.This method controls the phase difference between two orthogonal signals,and then,adjusts the polarization states in different frequencies.The co-polarization gain of operating band is suppressed out of band,thus achieving filtering characteristic.Meanwhile,the outof-band radiation power in the nulls can be absorbed by the isolated resistor,which has little influence on the former component in the communication system.② Based on this method,a circularly polarized filtering antenna working at 2.4 GHz is proposed by adopting the compact dispersive delay line with dramatic phase change.High selectivity can be observed.③A dual-band circularly polarized filtering antenna is provided with several radiation nulls.Based on the phase control method,four radiation nulls are achieved by only adopting the component of dual-band dispersive delay line,which solves the problem that most of dualband circularly polarized filtering antennas have complex structures.Good filtering performance can be achieved in both operating bands,and the structure of proposed antenna is quite simple.2.Dual-band dual-circularly-polarized directional microstrip antenna based on the phase control theory:①A low-profile dual-band dual-circularly-polarized antenna with small frequency-ratio is designed based on the phase control theory.The bandwidth of microstrip patch can become wider by introducing parallel coupling line,and the required polarization states can be realized by adjusting phase control component.②A wideband dual-band dual-circularly-polarized microstrip antenna is proposed.Here,the dual-band phase shifter is firstly introduced in the feeding network to realize the dual-band dualcircularly-polarized performance.The-10dB impedance bandwidths of proposed antenna are about 14.2%and 8.7%in two bands,and the 3dB AR bandwidths are about 24%and 10.9%.③A switchable dual-band dual-circularly-polarized antenna is proposed.Based on the abovementioned dual-band dual-circularly-polarized antenna,a symmetrical feeding network is added to introduce additional freedom.By controlling two pairs of single-pole single throws,polarization states can be switched and signal coupling can be suppressed.3.Omnidirectional circularly polarized microstrip filtering antenna based on the phase control theory:A circularly polarized omnidirectional filtering antenna is proposed based on phase control theory and filtering antenna fusion method.Firstly,based on the filtering antenna fusion method,radiation nulls are introduced at the stopband.As the parasitic patches of the omnidirectional circularly polarized antenna are evenly distributed around the main patch,thus we can individually adjust the filtering performance of each radiating element.Meanwhile,the out-of-band suppression of the antenna can be further optimized based on the phase control theory.Without adding additional circuits,a circularly polarized omnidirectional filter antenna that works at 2.4 GHz is designed.The operating bandwidth of proposed antenna is about 16.7%.The in-band gain is stable and the out-ofband gain is obviously suppressed.4.Omnidirectional circularly polarized helical antenna based on the phase control theory:The inverted normal-mode helix as well as the inverted and folded normalmode helical antenna/array are proposed based on the phase control theory,which solve the problems of conventional omnidirectional circularly polarized antenna/array,such as complex structure and large size.Firstly,the folded normal-mode helical antenna is proposed,which can easily provide omnidirectional circularly-polarized characteristic by applying simple structure,and also,solve the problems of low-profile input resistor and narrow bandwidth.Based on the inverted structure,the input resistor can be further increased by folding the helix.Finally,a four-elements antenna array is designed by adopting the inverted and folded helical antenna.Omnidirectional circularly-polarized characteristic can be obtained and the peak gain is about 7.9 dBic.