A modified doublet bandpass filter with substrate integrated waveguide -to- defected ground structure cell for bandwidth enhancement and source-load coupling

In this paper, a substrate integrated waveguide -to- defected ground structure (SIW-DGS) cell is proposed and used to implement a symmetric modified doublet filter. The utilization of proposed SIW-DGS cell can increase the coupling strength of the master transmission path in filter, thus resulting in the enhancing of bandwidth. And the source-load coupling generated by SIW-DGS cells can also improve the tuning flexibility of transmission zero. Measured results of the filter are in good agreement with the simulated ones, with a central frequency of 32GHz and a fractional bandwidth of 8.02%, as well as a transmission zero at 34.5GHz with notch strength over 55dB, and stopband with rejection below 25dB up to 50GHz.