Compact UWB filter with a reconfigurable notched band

In this paper, a design of compact ultra-wideband (UWB) bandpass filter with a ultra-narrow notched band is presented. The UWB frequency responses are achieved by using a microstrip-CPW broadside coupling structure. And a pair of side-coupled short-circuited microstrip lines is introduced to generate an ultra-narrow notched band. Based on this design, by loading a pair of varactor diodes at the end of the side-coupled short-circuited microstrip lines, a reconfigurable notched-band UWB filter can also be obtained, which can avoid the existing interferences such as the RF identification (RFID) signals (6.8 GHz) and WLAN signals (5.725~5.825 GHz) in the UWB frequency range. Commercial software ANSYS HFSS is used to analyze and design this filter. Simulated results show that it has good passband/stopband performances, compact size, and notched-band reconfigurability.