Computer-aided design of microstrip extracted-pole lossy filter

In this article, computer-aided design of a new type of microstrip lossy filter is described. The new type of lossy filter is realized by introducing resistive cross couplings into a microstrip extracted-pole filter to achieve a flat passband. The high selectivity is achieved by introducing 2 transmission zeros using 2 extracted poles, which can be adjusted. An equivalent circuit model is established and its circuit parameters, which are useful for physical implementation of the filter, are determined in light of computer modeling. For demonstration, two 6-pole filters centered at 2 GHz with fractional bandwidth (FBW) 6% and 20% are implemented. Experimental results, together with a theoretical comparison between different FBWs, and full-wave electromagnetic simulation results are also presented.