Design of absorptive bandstop waveguide filter without lumped-element

This letter presents one absorptive bandstop waveguide filter utilizing two couplers. The proposed absorptive bandstop filer (ABSF) with four ports is achieved by combing two quadrature couplers with two conventional waveguide bandstop filters, unwanted energy within the stopband will be absorbed by absorptive port instead of reflecting to incident port. The theory is analyzed and a waveguide bandstop filter with a center frequency of 12.85GHz is demonstrated and measured, the maximal stopband rejection is 70 dB with an input return loss of 19 dB, which implies that most of input power is dissipated by the proposed ABSF.