Design of Stepped Impedance Resonator BPF with Independently Reconfigurable Filtering Characteristic

A compact bandpass filter (BPF) with independent frequency reconfiguration is presented in this paper. Three resonators composed of two parallel-coupled lines with symmetrical configurations connected to two open termination stepped-impedance resonators (SIRs) and one coupled line with open-/short-terminated segment at the input and output of the filter creates the proposed BPF's independent reconfigurability. In the suggested BPF, these resonators are utilized to reduce the filter size and suppress the second and third harmonics which are considered as a crucial role in many applications. Three voltage-controlled varactor diodes are attached to the open SIR edges to create the reconfigurable filter with a tuning band. For verification, a reconfigurable BPF prototype operating in frequency tunning mode between 500 MHz and 1000 MHz with a 3-dB fractional bandwidth (FBW) that ranges between 16 % and 18 %. The filter's insertion loss ranges from 1.1 dB to 3.8 dB and their return loss ranges from 10 dB to 19 dB, according to measurement results. The proposed tunable filter has a compact size with dimensions of
$\mathbf{0.2}\ \boldsymbol{\lambda} \mathbf{g}\ {}^{\ast}\ \mathbf{0.22}\ \boldsymbol{\lambda} \mathbf{g}$
.