In this article, substrate integrated waveguide (SIW) based bandpass filter for radar application is presented. In the proposed design, bandpass response is achieved by combining SIW structure with dumbbells shaped defected ground structure (DGS) cells. Simulation of the proposed structure is carried out using commercial software Ansoft High Frequency Structure Simulator (HFSS). Frequency tuning is also carried out by changing the dimension of DGS. Moreover, equivalent circuit of the proposed filter has been derived and lumped circuit elements have been calculated using the circuit simulator in Keysight Advanced Design System (ADS) software. The measured return loss of 12.36 dB and insertion loss of 0.77 dB with 3 dB fractional bandwidth (FBW) of 5.71% at the center frequency of 7 GHz. Good agreements are observed between the experimental and the simulation results. Proposed filter will be utilized in the developed frequency modulated continuous wave radar system at CSRTC for the suppression of harmonics. 
Keywords: Substrate Integrated Waveguide (SIW), Defected Ground Structure (DGS), Filters, slow wave behavior