Compact Wideband Reflective/Absorptive Bandstop Filter With Multitransmission Zeros

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.