Digitally tunable bandpass filter for cognitive radio applications

A lumped-element tunable pre-selection bandpass is presented that consists of three coupled resonators. The bandpass employs a digitally tunable capacitor (DTC) and allows for tuning of the centre frequency with a resolution of 5 bit. It covers the frequency range from 450MHz to 940 MHz, including the DVB-T band, the TV white space (TVWS) band, and the LTE-800 frequency band. The insertion-loss variation amounts to 0.3 dB. The filter measures 20mm by 20 mm, it can therefore be easily integrated into analog RF front-ends. The filter's application to cognitive-radio platforms is discussed.