The design of microstrip six-pole quasi-elliptic filter with linear phase response using extracted-pole technique

The development of microstrip filters has been in great demand due to the r apid growth of wireless communication systems in this decade. Quasi-ellipti c response biters are very popular in communication systems because of thei r high selectivity, which is introduced by a pair of transmission zeros. A number of ways of implementing the quasi-elliptic response filter on micros trip have been studied over the last two decades, i.e., the cascaded quadru plet filter, canonical filter, and extracted-pole filter. However, there is very little information in the literature giving the design details for mi crostrip extracted-pole filters. In this paper, design equations of the ext racted-pole filter for microstrip are reviewed. A new class of microstrip f ilter is also presented here. This class of filter will have a quasi-ellipt ic function response and at the same time linear phase in the passband. The linear phase of the filter is introduced by an in-phase cross coupling, wh ile the transmission zero is realized using an extracted-pore technique. Ex perimental results, together with a theoretical comparison between the grou p delay of this design, and the conventional quasi-elliptic six-pole biter are also presented.