Research On Filtering Duplex Antenna With High Isolation

The integrated design of RF front-end system has become a new trend.The traditional RF front-end circuit is to design filters,diplexers and antennas separately and cascade them by matching circuit.This way not only enlarges the volume of communication system,but also degrade the performance of communication system.Duplex antenna is realized by the co-design of RF front-end devices for the purpose of miniaturizing and improving system performance.Frequency division duplex antenna with the same polarization adapts to the development of modern communication system and becomes a research hotspot.Because the transmitting and receiving signals are of the same polarization,it is necessary to introduce filtering networks to improve the isolation of transmitting and receiving signals in order to reduce the interference of transmitting and receiving signals.In this paper,different techniques are introduced to improve the isolation of the duplex antenna.In this paper,the high isolation filtering duplex antenna is taken as the research target,and the integrated design of duplex antenna is realized.The works are summarized as follow:1、A novel filtering duplex Antenna using split-ring resonators is proposed.Firstly,the working principle and resonance modes of the stacked duplex patches are analyzed.The transmitting and receiving filter are realized by coupling two split-ring resonators through a slot.The antenna serves as the last stage of the filter,and a duplex antenna with third-order filtering characteristics is designed.Due to the existence of patch isolation in stacked duplex patches,and the introduction of filtering networks improve the frequency selectivity and expands the bandwidth.Duplex antenna achieves a high isolation and a good filtering characteristics in its working band.2、A high isolation filtering duplex antenna with improved bandwidth is proposed.The dual-band antenna is realized by coupling a split-ring resonator and a radiation patch through the floor slot.The modes of the dual-band antenna is analyzed.Then the transmitting and receiving filter are composed of three quarter-wavelength short-circuit resonators,which can generate a transmission zero in its upper stopband.Duplex antenna with fourth-order filtering characteristics is realized by co-design of dual-band antenna and filters.The wideband and high isolation characteristic of the duplex antenna is realized by increasing the filter order and the transmission zeros generated by the filter in its upper stopband.3、A filtering duplex antenna with high isolation using controllable asymmetric transmission zeros.The dual-band antenna is realized by stacked patches.The modes of the dual-band antenna is analyzed.Then,the hairpin comb filter is introduced as the transmitting and receiving filter.By controlling the coupling length of the hairpin comb filter,the transmission zero of the transmitting filter is designed at the upper stopband,and the transmission zero of the receiving filter is designed at the lower stopband.Duplex antenna with third-order filtering characteristics is realized by the co-design of dual-band antenna and filters.Due to the introduction of the asymmetric zeros,the proposed duplex antenna achieves a high isolation and a good filtering characteristics.