Analysis of vertically installed planar (VIP) combline bandpass filters

A vertically installed planar (VIP) structure is adopted to create a two-stage combline type bandpass filter. It is basically a pair of 3-dimensional microstrip line resonators coupled very tightly. Addition of a fin capacitor and through-hole inductance at each end of the resonator controls the frequency of attenuation poles as well as the bandwidth. The equivalent circuit analysis gives an approximate but clear insight of the transmission characteristics, being supplemented by the rigorous FDTD analysis.