K-band suspended substrate stripline tapped combline filter

A newly developed 19.5-20.5 GHz combline bandpass filter realised by multiple coupled suspended substrate striplines (MCSSSs) and metal-insulator-metal capacitors is presented. The filter design uses an iterative field-theory-based algorithm to account for the composite effects of multiple dominant quasi-TEM modes of the MCSSS and the couplings through the nonadjacent lines. A prototype is built and tested. The measured and theoretical filter characteristics are in good agreement for the combline filter without any tuning.