Reconfigurable-order bandpass filter for frequency agile systems

This paper presents a tunable bandpass filter with a reconfigurable filter order. The proposed filter consists of an array of tunable resonators with variable inter-resonator coupling structures between adjacent cavities. This allows the frequency selectivity of the filter to be adjusted for the given spectral environment without any geometrical modifications to the filter structure. To demonstrate the concept a 2 × 2 resonator array is fabricated using substrate integrated evanescent-mode cavity resonators at 3.2 GHz. Each resonator has an adjustable frequency response and can be tuned from 2.77 to 3.55 GHz. The filter has two separate signal paths, either through two or four resonators. The reconfigurable inter-resonator coupling is implemented with floating vias inside a coupling iris. The vias are connected using variable capacitors and can be included or excluded from the iris by adjusting the capacitance. This structure shows the potential for the inclusion of reconfigurable-order filters in future agile radio systems.