Research Of Lumped Circuit And Microstrip Structure For LTCC Microwave Bandpass Filter

With the rapid development of the microelectronics information technology, electronic components tend to miniaturization, high frequency and integration as well as the rapid development of the mobile communication. The design of multilayer structure which based on LTCC (Low Temperature Co-fired Ceramic) technology has small size, low cost, reliable performance and was widely used in the filter, oscillator, mixer, antenna and so on.In this paper, the theory analyses and the magnetic-electronics simulation software are mixed to analyze and design the LTCC microwave bandpass filter. The main results and innovations are as follows:1. Research of folded Stepped impedance resonator (SIR). By using the odd and even mode, several network parameters and equivalent circuits of the coupled microstrip were drawn. By using of circuit analysis and electromagnetic simulation, the number of the transmission zeros and the resonances are same. We indicate and explain the separation of the resonant frequency by the distance of coupling. The size of the resonator can be reduced from 6mm to 1.8mm to realize the center frequency of 2.45GHz, reducing the size of the component.2. Design of the Lumped circuit. Including the design of passband, stopband, port and integrated circuit. The signal transmission combined with the analysis of circuit, we explain the location of the transmission zero .By using the series capacitor with resonator and cross coupling, transmission zero in the lower stopband can be realized. At last, two equivalent lumped circuits are derived to explain the location of the transmission zero at the lower stopband.3. Design of microstrip filter. Elctromagnetic coupling among the resonators will become more complex with reducing the distance. The filter is designed and simulated by using a full-wave electromagnetic simulator (HFSS). At last a bandpass filter with the center frequency of 2.45 GHz was designed and fabricated by using the parallel-coupled folded SIRs. The area occupied is 2.5×2.0×0.9/mm~3. Simulation result shows less than 1.7dB insertion losses at the center frequency.