Switchable Bandpass Filter for 0.3-0.6 GHz

A switchable filter topology is proposed in the form of a self-scalable comb-line structure. This topology is capable of implementing a tunable frequency response with consistent performance over very large tuning ranges. A two-pole prototype has been fabricated using 10 discrete PIN diodes and is capable of covering the frequency range of 290 to 600 MHz in four steps (2-bit tuning). The in-band loss of the filter is better than 2 dB for all modes when a DC voltage of 5 V is used for biasing the PIN diodes. The filter has a IIP3 of greater than 32 DBR, and its RF structure occupies an area of 9 times 21 mm².