Theoretical research and ADS simulation of tunable band-pass filter

In RF transceiver system, it is necessary to add a tunable band-pass filter in the system to solve the problem of frequency congestion and improve the system's anti-interference performance. The circuit structure with a continuous tunability for both the resonant frequency and bandwidth which is constant is presented theoretically in this paper, the resonance circuit is viewed as a resistance at the resonant frequency, T inductance coupling is adopted, ADS is used to simulate and verify. The simulation results show that the center frequency varies from 66 MHz to 72 MHz while the resonant capacitance changes from 60 pF to 50 pF and bandwidth keeps 5 MHz, the bandwidth reduces from 5 MHz to 3.5 MHz when the coupled inductance decreases from 58.186 nH to 40.532 nH, the filtering performance is good at the tuning frequency point, the insertion loss increases about 0.223 dB when tuning the bandwidth and it slightly reduces the system performance but meets the requirements of RF communication, the filter's analyses in the paper provides a theoretical basis for the practical production.