Compact UWB bandpass filter with reconfigurable notched band

A compact bandpass filter is presented for ultra-wideband (UWB) applications with a reconfigurable notched band to reject unwanted signals from the WiMAX systems. A single pin diode is used for the purpose of switching the notch. An optical switch, comprised of a silicon dice activated using near infrared light is also investigated as an alternative to the pin diode. While the switch is in the ON state this reconfigurable filter behaves as a bandpass filter with a notch at 3.5 GHz and a full band response is obtained in the OFF state. The filter offers excellent performance for the lower-band frequency of a UWB system, ranging from 3.1 to 5.0 GHz and exhibits very low passband insertion loss. Also, transmission zeros are generated at the passband edges to enhance the signal selectivity. A filter sample has been designed and fabricated to provide experimental verification on the proposed filter. A good agreement has been achieved between simulated and measured results with both the pin diode as well as the optical switch. The proposed reconfigurable filter with notched band was able to achieve 40% size reduction as compared to an embedded open-circuited stub.