Compact switchable filter for software-defined radio

A switchable bandpass filter includes a coupled line segment (comb) including a plurality of coupled transmission lines of substantially equal lengths that are each connected or otherwise coupled to the common RF ground at their first end, a plurality of adjustable capacitors each coupled proximate a second end of respective ones of the transmission lines, and a plurality of shunt switches coupled to points along a length of each of the transmission lines. Shunt switches may be implemented by various device technologies including MEMS and FET switches and PIN diodes. The adjustable capacitors may be implemented as an array or tree of switched capacitors using suitable switching components (e.g., as previously enumerated) or by other suitable electrically controllable devices such as varactors or varactor arrays. A differential switchable filter may be formed by the symmetric repetition of individual bandpass filter modules.