Reconfigurable BPF with Wide Tuning Bandwidth Range Using Open- and Short-Ended Stubs

In this paper, a reconfigurable bandwidth bandpass filter (BPF) is demonstrated operating at a fixed center frequency of 2.4 GHz. The proposed reconfigurable filter is based on a quadruple-mode square ring resonator loaded with either λg/4 open-ended stubs or λg/2 short-ended stubs to implement two reconfigurable bandwidth states. Due to symmetrical design, even- and odd-mode analysis is performed and closed form equations are derived to describe the reconfigurable filter behavior. PIN diodes are used to switch from narrowband state to wideband state. In order to suppress the higher order modes and to improve the upper stopband, a pair of parallel coupled lines (PCLs) and a pair of λg/4 high impedance short-ended stubs are placed at the input and output ports. To verify the validity of the simulated results, the prototype of the proposed reconfigurable filter was fabricated. The measured results demonstrate a low insertion loss less than 1 dB and a 3-dB fractional bandwidth (FBW) that can be switched from 34% to 75% while the center frequency is kept constant at 2.4 GHz.