Compact bandwidth tunable IF filters for reconfigurable converters

This paper aims to present some outcomes from a European Space Agency (ESA) Technology Research Programme (TRP) project on R&D of new design techniques, concepts, and filtering configurations for tunable IF (intermediate frequency) filters with a compact footprint, wide bandwidth tuning range (covering from 49 to 478 MHz at f(0) = 1 GHz) as well as equivalent high-Q performance (i.e. low insertion loss variation and high selectivity by using low-Q resonators). In order to obtain a wide tuning range, the proposed filtering configuration utilizes a new tuning technique that only necessitates control of coupling values with simple DC control circuits, without the need of tuning the electrical length of resonators to avoid deviating the center frequency. Furthermore, in order to achieve the equivalent high-Q performance, a novel lossy technique by using a centrally resistor-loaded half-wavelength resonator is adopted. For the proof of concept, a six-pole prototype filter is designed, fabricated, and tested.