Simple design formula for parallel plate mode suppression by ground via-holes

In a multi-layered RF circuit, it is important to avoid unexpected coupling caused by a parallel plate mode excited between different ground layers. Ground via-holes that short-circuit different ground layers are used for suppressing this mode. Quantitative evaluation of relations between suppression effect and ground via-hole disposition is required for optimal design. In this paper, a simple design formula that describes the suppression ratio is derived by mode-matching technique. The results of comparison with an FEM simulation validate our proposing formula. It is shown that the technique is indispensable for designing optimal disposition of via-holes to minimize the area of the ground via-holes for desired performance.