Reconfigurable single/multi-band planar impedance transformers with incorporated bandpass filtering functionality

A new class of frequency-agile single/multi-band planar real-impedance transformers that feature bandpass filtering capabilities for their operative bands are proposed. They are based on the incorporation of single/multi-band quasi-bandpass filtering sections into a wide-band impedance transformer whose operational range covers the intended frequency-tuning range of the individually-controlled passbands. Thus, by controlling the natural frequencies of the resonators in these sections through variable capacitors, a tunable single/multi-band impedance-transformation/bandpass-filtering action is obtained. The operational foundations of this reconfigurable dual-function device, which can be applied to designs with an arbitrary number of bands, are expounded. Furthermore, as experimental demonstration, a three-band microstrip prototype with tunable bands throughout the range 1.2-1.8 GHz is developed and tested.