Suspended Stripline Filters Integrated with Standard Multilayer Printed Circuit Boards

Suspended stripline (SSL) is a good transmission line medium for the realization of filters. One drawback, however, are problems in integrating such filters into extended circuits. To overcome this problem, different SSL filters were designed and tested, realized on a multilayer board consisting of a standard printed circuit board (FR4) and a microwave substrate laminated on top. The necessary channel for the SSL is formed by rows of vias in the multilayer together with a cap fixed on top of the filter structure. While lowpass and highpass filters easily show good results, a higher fabrication accuracy and the inclusion of dielectric dispersion and anisotropy of the FR4 material is necessary for good results of bandpass filters.