Wide-passband filters with in-band tunable notches for agile multi-interference suppression in broad-band antenna systems

Sharp-rejection and low-loss planar wide-band bandpass filters with embedded in-band frequency-agile notches, that are useful for dynamic multi-interference mitigation in broad-band antenna systems, are presented. The proposed RF filter concept consists of in-series-cascaded transversal signal-interference filtering cells with an embedded tunable quasi-absorptive-type notch in the transmission range of each of them. Each of these cells is made up of three signal-propagation paths in which one of them is reused by both filtering functionalities. This leads to smaller footprint as opposed to conventional solutions based on in-series cascades of separate filtering units. Furthermore, the in-band tunable notches can be spectrally merged so that the number of active rejection bands in the passband is dynamically controlled. For experimental-demonstration purposes, a 2-GHz two-stage microstrip prototype with two independently-tunable quasi-absorptive-type notches is developed and characterized.