Compact 2-pole and 4-pole 2.4–2.8 GHz dual-mode tunable filters

Compact 2-pole and 4-pole dual-mode tunable filters have been developed to cover the 2.4-2.8 GHz bandwidth. The filters are based on magnetic coupling (2-pole) and on a mixed-mode coupling (4-pole) so as to result in a near-constant fractional bandwidth over the tuning range. An unloaded tunable filter Q of 50-130 was achieved for both designs, which is quite high when using Silicon Schottky varactor diode for the tunable elements. The filters are integrated on an εr = 10.2 substrate, are quite small, and result in relatively low insertion loss (2-6 dB) and excellent rejection. The application areas are in reconfigurable communication systems.