Bandwidth deviation controlled reconfigurable bandpass filter using LC parallel coupling circuit

Mobile terminals are required to cover wide range of RF frequencies for the enhancement of mobile communication systems. Thus reconfigurable RF circuits for the terminals attract much attention because they flexibly change many frequency bands under the control of the communication systems. Reconfigurable bandpass filter (BPF) with eight-frequency selection capability has been studied for this goal. However, one of the design issues is how to control passband bandwidths among selectable frequencies. In this paper, bandwidth deviation is analyzed for the reconfigurable BPF that consists of two stages of branch-line switched type variable resonators and J-inverter coupling. By calculating external Q and coupling coefficient, it is shown that the LC parallel coupling design can achieve less deviation of bandwidth for the reconfigurable BPF. The design is validated by the evaluation of prototype circuit.