Post-Loaded Substrate-Integrated Waveguide Bandpass Filter With Wide Upper Stopband and Reduced Electric Field Intensity

In this letter, we present analytic approaches to obtain a wide upper stopband and to reduce the magnitude of the electric field intensity in designing a bandpass filter using the fundamental mode of post-loaded substrate-integrated waveguide (SIW) resonators. As the filter is made with two commercially available substrates, there are two dielectric and three ground layers. This letter particularly shows that the ground layer in the middle has an impact on the upper stopband and the electric field intensity and proposes a methodology to control them. For demonstrating our new approach, we have designed a third-order filter centered at 5 GHz with the bandwidth of 330 MHz.