Research On Dual Passbands Electronically Tunable Microstrip Filters Design

Mobile wireless communication has become an essential and indispensable tool in our daily life. Filters are very important in communication systems, the performance of the filter directly influences the quality of the communication signal. Electrically tunable filters can be miniaturized, have high integration and high complexity, and are gradually replacing conventional filters. Research on Electronically Tunable Filters has great significance.In this paper, a continuous electrically tunable filter and a discrete electrically tunable filter that are based on a varactor and RF-MEMS respectively, each having two passbands are designed. The main work are summarized as follows:Firstly, the index parameters of the designed electrically tunable filter and the conversion method of the low pass prototype filter to the microstrip filter is proposed. Several electrical adjustment methods of electrically tunable filter are analyzed and summarized. The plan varactor and RF-MEMS network respectively used to design continuous tunable filter and discrete tunable filter is proposed.Secondly, the stepped impedance resonator structure characteristics and resonance characteristics are analyzed. The characteristics of the varactor are also analyzed and simulated. One end of the varactor is connected to the center of the SIR, while the other end is connected to the T-shaped resonator,a continuous electrically tunable filter is designed. A filter network and spurlines are added at the input and output coupling line to depress stopband,a continuous electrically tunable filter with wide stopband is designed. Simulation results and experimental results are in close agreement, which verified the effective of the design.Finally, a novel UWB filter based on the typical UWB filter is designed. The T-shaped resonator is analyzed and simulated, the change regulation of the center frequency is obtained,a UWB filter with dual bands is designed. The parameters' characteristic of RF-MEMS switch network are analyzed, a set of RF-MEMS switching network with four tuning states is designed. The simulation verified the feasibility of working at high frequency. The RF-MEMS switching network is loaded on the UWB filter and the digital electrically tunable UWB filter is realized. The simulation results demonstrate that the filter achieves design requirement.