X-band Tunable Filter Based On RF-MEMS Technology

With the development of modern communication technology, communicationsystems are increasingly demanding on high integration and miniaturization of thedevice, the traditional filter has not fully adapt to the demand. Using tunable filter notonly reduce the size of the system, but also meet the requirements of communicationprotocol multiplexing, therefore the design of the tunable filter has become one ofresearch hotspots in recent years. Some researchers put the radio frequencymicro-electro-mechanical system (RF-MEMS) into the filter design, developed a highlinearity, small insertion loss and isolation of high electric tunable filter. At present, thedomestic for tunable filter based on the technology of RF-MEMS research started soon,the literature detailed description of this kind of filter design method is scarce.In this paper, design of RF-MEMS tunable filter using mems switch network loadin the resonator microstrip line terminal, realizes the tunalble filter center frequency bychanging the equivalent capacitance value of the switch network. First, the idealvariable capacitor to replace the mems switch network and according to therequirements of the filter design index calculated physical parameters of the resonatormicrostrip line and the capacitance value of the variable capacitor, and then designphysical structure of mems switch network according to the capacity value size. In orderto verify the effectiveness of the proposed design scheme, this paper design a8.5-10.5GHz tunable filter which has four tuning state, the tuning unit is used by switchcapacitor network which is made up of metal-air-metal (MAM) capacitance and memsswitch. This paper adopted a separation design for microstrip circuit parts andRF-MEMS switch network, compared the simulation results and calculation results, andalso analyzes the characteristics of mechanical and electrical switch network in order totest the switch network can work normally, In addition, the linearity of the switchnetwork also has carried on the analysis and simulation.When mechanical and electrical characteristics of switch network meet the designrequirements, simulate the whole tunable filter, and the center frequency of four tuningstates is8.5GHz,9GHz and9.8GHz and10.65GHz, insertion loss is less than2dB, therelative bandwidth is3%, achieved the desired design goal.