A novel microstrip absorptive bandstop filter

A novel absorptive bandstop microstrip filter utilizing two couplers is presented in this letter. The proposed absorptive bandstop filer (ABSF) with four ports is achieved by combing two quadrature couplers with two conventional microstrip bandstop filters. Unwanted energy within the stopband will be absorbed by absorptive port instead of reflecting to incident port so that the property of absorption could be realized. The theory is analyzed and a microstrip bandstop filter with a center frequency f0 of 5GHz is demonstrated and simulated, the maximal stopband rejection is 38 dB with an input return loss of 31 dB, which implies that almost of the input power is dissipated by the proposed ABSF.