Transmission zero controllable bandpass filters with dual and quad-band

Microstrip dual and quad-band bandpass filters with triangular stepped-impedance resonators are developed by using separate electric and magnetic coupling paths. Either the magnetic-dominant coupling or the electric-dominant coupling generates a transmission zero (TZ) but at different positions and the corresponding TZ can be controlled and adjusted by controlling the electric or magnetic coupling coefficient. Both the electric and the magnetic-dominant couplings generate a pair of TZs, but the additional coupling resonators are not required. The new designs have been demonstrated by measurement. Advantages of the new filters are not only their compact circuit topologies, miniature circuit sizes, independently controllable filter operation frequencies, but also their controllable TZs.