Design Of High Performance Waveguide Diplexer For Wireless Communication System

The growth of user demand and the innovation of new technology put forward higher requirements for communication technology.The integrated design of the traditional indoor system has been gradually abandoned by the corresponding microwave communication equipment,and the split structure,consisting of outdoor transceiver,indoor modulation-demodulation and baseband interface,has become a mainstream for its smaller size and easier removal.As the important component of the communication equipment,diplexer is responsible for the selection,synthesis and separation of transmitting and receiving channel.In this paper,the diplexer works in the pilot frequency diplex mode and is widely used in microwave ODU transceiver system.Under the frequency selection function of the Tx filter and Rx filter,the diplexer allows the system to receive and transmit signals by sharing one antenna.How to realize high performance requirements of the diplexer at low cost has always been an important issue.Based on the high-performance waveguide diplexer scheme,this paper's work mainly includes:1)The Ku band waveguide diplexer design.The Y matrix method is inapplicable for the waveguide diplexer tuning in this frequency range,because the single cavity resonant frequency calculated by the Y matrix has 0.9%~2% deviation in Ku band.Thus,?Wave Wizard,which is a software based on pattern matching method,is used to optimize the initial size.The test results show that return loss in pass band is 18 dB,and the rejection of Tx passband is higher than 68 dB within 15.138~15.348 GHz,while the rejection of Rx passband in 14.718~14.942 GHz is over 65dB;2)The wide stopband waveguide diplexer design.The general waveguide diplexer structure often produces a parasitic passband,which makes it impossible to obtain a good out-band suppression in the far frequency range.To realize wide stopband characteristics of waveguide diplexer,the diplexer presented above and the evanescent mode waveguide filter with wide distal suppression are integrated into the cavity.The simulation value of out-band suppression is greater than 40 dB in 21.2~43GHz;3)The waveguide diplexer design with wide stopband and high isolation.Through the integrated design of the circulator and the wide stopband waveguide diplexer,the Rx and Tx port of diplexer no longer needs to be connected with an extra circulator in the communication system.HFSS simulation results show: the isolation of Rx to Tx port is up to 110 dB,about 50 dB higher than wide stopband diplexer and the reverse isolation of Tx to Ant port and the Ant to Rx port is greater than 23 dB,which means one-way signal transmission is available.These results prove the scheme's feasibility.In the process of completing all the designs,according to the problem that negative cross coupling is difficult to realize for waveguide diplexer structure,a simple method to achieve transformation from positive to negative coupling and some theoretical analyses about this method are given by this paper.Besides,a new bending structure with 34.9% shorter length than linear pattern of the evanescent mode waveguide filter is also presented in this paper.