Parallel-coupled switched delay line (SDL) reconfigurable microwave filter

Conventional realizations of varactor-loaded tunable filters exhibit high losses due to the degradation of Q factor caused by varactor's losses. These filters also suffer from nonlinear-related problems such as intermodulation distortion due to varactor nonlinearity. In this paper, a new class of parallel-coupled SDL reconfigurable filter is shown. Theoretical analysis together with experimental prototype is presented. The filter provides narrowband quasi-elliptic filter response with constant bandwidth (50 MHz) tuning across 45% tuning range. The minimum stopband rejection level is 45 dB and it possesses passband loss of < 4 dB and an IP3 of >32 dBm for deltaf = 1 MHz.