Switchable Filter with Four Operating Modes Implemented on a 50-Ohm Microstrip Line

In this paper, we implement a compact switchable bandpass filter on a 50 Ω microstrip line. The proposed structure consists of an input/output stage with one end terminated at 50 Ω, a C-shaped-open loop resonator, and two L-shaped-open loop resonators. The proposed filter operates in four different modes depending on the on/off combination of the five PIN diodes. Each mode includes a dual-band pass filter (DB-BPF) designed for the 1.4 GHz and 5.1 GHz bands, another DB-BPF covering the 2.4 GHz and 4.2 GHz bands, a wideband BPF with a bandwidth ranging from 2 to 4.5 GHz, and an all-pass filter (APF) that allows all frequencies to pass through. The proposed structure is extremely compact because it is implemented on a 50 Ω line without any additional space.