Research On Duplex Antennas

With the development of wireless communication system,to make the system with compact structure,light weight,and be easy to carry,the antenna and transceiver are usually integrated with each other,which makes the integration design of the RF front-end antenna and transceiver become a new development trend.The traditional strctures of receiving and transmitting antenna empoly microwave isolated device to connect the antenna or apply double-antenna system.These sturctures are easy to bring volume,weight,loss,isolation and other shortcomings to the RF front-end.In this paper,the co-frequency duplex antennas are designed in the form of a simple structure to achieve high isolation and the FDD antennas are designed with the integration of antenna and duplexer or filter.The FDD duplex antenna employs the integration of design of the antenna and duplexers or filter,which will make the antenna compact,and improve the integration of the antenna-feed system,moreover,the operating bandwidth and isolation characteristics of the antenna are enhanced.This paper mainly studies the design methods of two kinds of microstrip duplex antennas of the different frequency and polarization and the co-frequency orthogonal polarization,and presents duplex antennas with several kinds of structures and different application.The details are summarized as the following five parts:1.A co-frequency dual polarization duplex antenna based on the hybrid ring feeding is proposed.A dual polarization duplex patch antenna based on 180 degree hybrid ring is firstly introduced.On the basis,a high isolation,low cross polarization dual polarization microstrip duplex antenna based on the new hybrid ring feeding network is designed.Compared to the 180 degree hybrid ring dual-polarization microstrip duplex antenna,the ports isolation of this antenna is raised about 7 d B,it is up to more than 42 d B.And the cross polarization is greater than 30 d B.Finally,a high isolation and low cross polarization broadband dual polarization duplex antenna is proposed.The antenna can implement in a wider range of frequency band with high port isolation,the isolation is higher than 40 d B within most of the passband,the cross polarization of the antenna is higher than 24 dB,and the relative impedance bandwidth of the antenna is 38.7%.2.A co-frequency dual circularly polarized duplex antenna applied in RFID system is proposed.The antenna is mainly composed of two nested ring patch,a pair of orthogonal placed H slots etched on the ground plane and a dual-band branch line coupler.The dual ring patch realizes the dual band operation,the H slots works as a coupling device and offers the spatial orthogonal electromagnetic waves for the patch,and the dual frequency branch line coupler works as the feeding network and provides equivalent magnitude and continuous orthogonal phase signals to the H slots,which coupled to the patch to produce circularly polarized wave,the dual frequency branch line coupler enhances the transmitting-receiving port isolation,as well.When one port is excited,the antenna can produce left-hand or right-hand circularly polarized wave,another port is excited,antenna can generate the corresponding orthogonal polarization circular polarized wave.The RFID reader antenna launches signal to the tag antenna,and receives the reflected signal from the tag antenna at the same time with this structure.The antenna realizes the ability to transmit and receive simultaneously.The experimental results show that the dual circularly polarized dual frequency duplex antenna is with 5.2 d Bi gain at 915 MHz(UHF),and 6.4 d Bi gain at 2.45 GHz(ISM);the ports isolation according to the above mentioned frequencies are 30 d B and 25 d B,respectively;the axis ratio in the UHF frequency band(890-930 MHz)is below 2.6 d B,and axis ratio in the ISM frequency band(2400-2500 MHz)are lower than 1.1 dB.3.A FDD duplex antenna based on the coupled resonator is proposed.The duplex patch antenna consists of two radiation patches,a pair of H slots resonators and a pair of microstrip resonators.The Two radiation patches offer bidirectional radiation and work as a synthesis cavity of duplex,the H slots resonators function as a coulping and resonating device,the microstrip resonators together with the H slots resonators worked as two two-order bandpass filtering performances.The overall design make the antenna work in a small transceiver frequency space with high transmitting and receiving isolation and filtering performance.By studying the parameters of the spacing of the H slots,the air layer height and the coupled spacing between the H slots resonators and the microstrip resonators,the effects of these parameters to the antenna are analyzed.Based on the design of the duplux antenna element,a 2 x 1 duplex antenna array is designed,too.The experimental results show that the antenna array has a transmitting passband from 1.94 to1.99 GHz and a receiving passband from 2.43 to 2.52 GHz,the ports isolation is up to 30 d B and 40 d B in the passband,and the transmitting and receiving frequency is only 0.23 times of the center frequency of the two passbands,the gain of the transmitting passband is 4.85 d Bi,and the restraint level to the receiving passband is 25 d Bi,the gain of the receiving passband is 2.46 d Bi,and the restraint level to the transmitting passband is 27 dBi.4.A FDD filtering duplex antenna employed asymmetric transmission zeros is proposed.The antenna consists of a radiation patch,two pairs of T-shaped probes and two filters.Firstly,the structure and the equivalent circuit of the broadband antenna with two resonant points are firstly described and analyzed,then the design of the transmitting and receiving filtering antennas are introduced,and the performances of the integrated filtering duplex antenna and the cascaded duplex-antenna are compared.The experimental results show that the antenna has a 10.6%(1.95 to 2.17 GHz)transmitting passband bandwidth and 6.9%(2.5 to 2.68 GHz)receiving passband bandwidth,and the transmitting and receiving frequency is only 0.23 times of the center frequency of the two passbands,the ports isolations in the two passbands are higher than 45 d B,the gain of the transmitting passband is 5.74 d Bi,andthe restraint level to the receiving passband is 36 d Bi,the gain of the receiving passband is 4.6 d Bi,and the restraint level to the transmitting passband is 30 d Bi.5.A FDD antenna applied in WCDMA is proposed.The short circuit chip loaded in the square ring patch and the stacked parasitic patch realize the dual frequency operation,the dual-mode resonators coupled to the dual-frequency patch to produce a transmitting antenna and a receiving antenna,the two antennas share the same radiator to form a duplex antenna.By introducing asymmetric transmission zeros and changing the coupling pattern of the port,which will further increase the numbers of the transmission zeros,the filtering duplex antenna can achieve the high ports isolation performance.The experimental results show that the antenna has a 70 MHz(1.937 to 2.07 GHz)transmitting passband bandwidth and 76 MHz(2.106 to 2.182 GHz)receiving passband bandwidth,mostly covering the passbands of the TDD WCDMA,and the transmitting and receiving frequency is only 0.09 times of the center frequency of the two passbands,the ports isolations in the two passbands are higher than 32 d B,the gain of the transmitting passband is 6.8 d Bi,and he restraint level to the receiving passband is 27 d Bi.the gain of the receiving passband is 6.6 d Bi,and the restraint level to the transmitting passband is 31 d Bi.Based on the above five kinds of duplex antennas,the working principle and design method of the antenna system are explored and researched,which enrich the theory of duplex antenna structure and design.