Yaractor-based microstrip circuits with high frequency agility and low insertion loss

The authors present a straightforward and effective approach for minimizing insertion loss (IL) of varactor-based frequency-agile microstrip passive circuits, where varactors are employed as elements of variable reversal capacitances to attain reconfigurabiltiy/tunability on circuit characteristics. Technically, the proposed approach mimics the required capacitances using the varactors together with the SMD capacitors/inductors rather than entirely using the varactors. With the proposed capacitance synthesis, the varactors are able to operate at a higher quality factor so that IL of the entire circuit is minimized. Also, the capacitance tuning range is further extended. With the proposed loss-reduction avenue, the circuit agility could be enhanced, and its effectiveness is experimentally demonstrated with agility enhancement of a reconfigurable bandpass filter (BPF) and a reconfigurable balun BPF.