Research Of Mult-band Filter/Antenna In Communication System

With the rapid development of communication industry, communication systems need towork at mult-frequency bands, the communication devices’ miniaturization and portable needto improve, and this put forward higher requirement for the communication equipment withhigh efficiency and low cost and so on. As a part of the front communication equipment end,improving microwave/RF circuits and system integration is beneficial to reduce cost and thecomplexity of the equipment, and can reduce device power consumption, improve efficiency,achieve the purpose of green energy-saving communication. Communication systems usuallyneed to be compatible with various frequency band signals to increase the system integration,mult-band microwave device is the key device at transceiver front-end, have become aresearch hotspot. The main research of this work as follows:(1) A compact tri-band bandpass filter (BPF) using stub-loaded open-loop multi-moderesonator and asymmetric coupling lines is presented in this letter. The multi-mode resonatorcan generate three odd modes and three even modes in the desired passband. Odd-even modetheory is used to analyze the characteristics of the resonator, there are several transmissionzeros (TZ) near the passband edge, and they can improve selectivity and stopband suppression.Meanwhile, transmission zeros can be controlled by tuning the asymmetric coupling lines.The filter is applied for GSM (0.88-0.96GHz), GPS (1.57GHz) and DCS (1.71-1.88GHz).(2) A short stub loaded resonator based on asymmetric stepped impedance is proposed,the filter is worked for GSM (1.9GHz) and LTE (2.4GHz) dual-band communication system.The characteristics of the resonator are analysed by odd-even mode theory combined with theodd even mode equivalent circuit of resonant modes. A concrete analytical relationshipbetween resonators resonant frequency between impedance ratio and electrical length ratios isshown; and analysing source-load coupling strength effecting on transmission zeros.(3) The proposed microstrip-fed tri-band bow-tie antenna forms three operating bandsby inserting two pairs of slots with different lengths on the isosceles triangle microstrip patchwithout increasing the overall antenna area. Two pairs of slots are etched on the isoscelestriangle microstrip patch resonator to change the surface current distributions resulting intri-band for WiMAX (3.47-3.51GHz), INSAT (4.54-4.60GHz) and WLAN (5.75-5.81GHz).Because the antenna generates three bands, which can greatly reduce the antenna size, weightand circuit complexity, this can significantly improve electrical performance of antenna.Meanwhile, the direction of the antenna has good radiation characteristics and gain, suitablefor mult-band wireless electronic equipment.