A Compact Multi-Layered Ultra-Wideband (UWB) Bandpass Filter with a Built-In Band-Rejection Filter

This paper proposes a compact multi-layered ultra- wideband (UWB) bandpass filter including a built-in band- rejection filter, for preventing the UWB communications from interfering with already-existing wireless communication systems. The band-rejection response obtained can be controlled flexibly by changing a coupling capacitance to the closest parallel metal plate or to the ground enclosure. In the finite element analysis and equivalent circuit simulation, a UWB performance of around 90% relative bandwidth and a widely-controllable band-rejection response were obtained. Also, experimental results show good agreement with those theory. This compact filter, originally designed based on the heft-handed composite right-/left-handed (CRLH) transmission line theory [1, 2], has a perfectly-shielded structure, a moderate group delay and excellent out-of-passband characteristics.