A band-switchable and tunable nested bandpass filter with continuous 0.4–3GHz coverage

This paper presents a second-order tunable bandpass filter (BPF) with continuous 0.4-3GHz coverage for software defined radio (SDR) transceivers. The band-switchable and tunable BPF is realized with two pairs of RF-switches for coarse-tuning and RF-MEMS tunable capacitors for fine-tuning. Transition between 3 bands is enabled using two pairs of RF-switches. Furthermore the 3-bands switchable BPFs are constructed in nested filter bank structure for expanding tuning range without increasing foot print. In addition, to complement the discrete band gaps, RF-MEMS capacitor tuned resonators are used, and contiguous tuning range of nearly entire UHFband is achieved. The filter is fabricated on a Duroid substrate with ε
_r
=3.5 and h=0.787mm. The proposed nested tunable filter shows an insertion loss of 3.2-6.8 dB and a 1-dB bandwidth of 65-450 MHz with a contiguous tuning range of 0.4-3 GHz.