Compact Reconfigurable Triple Bandstop Filter Using Defected Microstrip Structure (DMS)

Abstract

In this paper, a low-profile triple-notched bandstop filter (BSF) is introduced. The proposed filter suppresses frequencies of Bluetooth (2.4 GHz), Wi-Max (3.5 GHz), and Wi-Fi (5.2 GHz) using three defected microstrip structures (DMSs). This BSF may be located in the feed line of an ultra-wideband (UWB) antenna. Consequently, not only the complexity is reduced, but also the area of the presented filter (24 × 10 mm2) is plummeted. Multiple rectangular slots are etched in the feed line to achieve multi-notch performance. Additionally, two dumbbell-shaped defected ground structures (DGSs) are etched in the ground plane to improve matching. Three PIN diodes are used to reconfigure the frequency response of the filter. By controlling the three diodes, the proposed filter can support six operating modes. The filter is simulated, optimized, fabricated, and measured to be suitable for cognitive radio applications. It achieves an insertion loss of (40, 29, and 24) dB and a rejection rate of (184, 215, and 277) dB/GHz at 2.4, 3.5, and 5.2 GHz, respectively. The simulated and measured results agree well.