Filters are the basic component of transceivers and receivers in the RF front-end communication system, either as band reject or band select units. This research is about an investigation of the new switchable filter which is can switch from matched bandstop to bandpass filter based on lossy resonator, where the lossy resonator topology can be used to partially compensate for the loss. The aim of this research work is to investigate the switchable matched bandstop to the bandpass filter response using lossy resonator based on EM modeling. This filter will be realized in parallel-coupled L-shape resonator. A PIN and varactor diodes will be used to make the filter switchable. This switchable filter provides two modes of operation; matched bandstop and bandpass response. The operating frequency is 2.4 GHz. The theoretical analysis together with EM modeling of the new switchable matched bandstop to bandpass response are presented in this paper.