Compact Wideband Reflective/Absorptive Bandstop Filter With Multitransmission Zeros

Abstract

Novel wideband reflective bandstop filters (RBSFs) and absorptive bandstop filters (ABSFs) with high stopband rejection (SR) and good frequency selectivity are proposed. Based on a coupled line (CL) with an open-circuited stub, a broad stopband response with three transmission zeros (TZs) is implemented in a compact circuit configuration. Two modified CL structures are loaded at the ports resulting in two additional TZs. In addition, a grounded resistor is introduced to absorb unwanted signals in the stopband. For demonstration, the five-zero RBSFs and three-zero ABSFs operating at 2 GHz are designed and built. The reflective filter shows a 35-dB SR with 79.5% relative bandwidth (RB). The absorptive filter with 69.5% RB of 24-dB SR achieves an all-passband 12.2-dB return loss. Good agreements between simulated and measured results are observed.