Two-stage reconfigurable bandpass filter using two-bit variable-length transmission line resonator

In order to make more efficient use of radio spectrum and reduce RF circuit size of future mobile communication terminals, reconfigurable RF circuits will be necessary that can flexibly change larger number of frequency bands. This paper presents a two-stage two-bit reconfigurable bandpass filter employing two-bit variable-length transmission line resonator. The resonator consists of a λ/4 resonant-mode tapped transmission line with two RF switches and can choose one of four resonant frequencies according to the status of the switches. The two-stage bandpass filter is designed by J-inverter method. Its frequency response is analyzed by EM simulation including loss due to the RF switches and effects of interstage coupling. Prototype BPFs using micro strip lines on a high dielectric substrate have been fabricated and showed low insertion loss from 1.5 to 2.1 dB for the four center frequencies in 2.0 - 2.5 GHz band.