Fully-reconfigurable bandpass filter with static couplings and intrinsic-switching capabilities

A transfer-function-adaptive quasi-elliptic-type microwave bandpass filter is presented. The devised fully-reconfigurable filter is based on a resonator-cascade structure with static impedance inverters and only exploits the tuning of its resonating nodes to achieve all its reconfiguration properties. They include center-frequency, bandwidth, and transmission-zero (TZ) control for bandpass-type responses, as well as the intrinsic switching-off - i.e., without RF switches - of the filter. Moreover, it features less in-band insertion-loss levels and improved linearity behavior - specially for narrow-band states - when compared to more-classic bandwidth-tunable filters that use inter-resonator coupling variation. The operational foundations of the engineered fully-reconfigurable filter architecture are theoretically expounded in a coupling-matrix framework. Besides, a tunable three-pole microstrip filter prototype in the range 1.2-1.7 GHz is developed and tested for experimental-demonstration purposes.