Microstrip Filters at High Frequencies

Advisor: Prof. Wilson Pearson

Microwave filters have evolved from bulky brass or gold-plated brass cavities to printed realization in the ubiquitous medium of microstrip transmission lines. Performance of microstrip filters suffer because of the loss intrinsic to the microstrip format. In this project, we shall determine the extent to which one can realize sharp separation boundaries between the passband and the stopband in microstrip filters. Elliptic filter design provides a methodology for crowding passband poles and stopband zeros closely in order to derive a sharp transition theoretically. However, the material losses present in the microstrip format tend to "smear" the transition and produce results that fall short of the theoretical prediction. We shall design and fabricate elliptic filters at frequencies as high as K band (18-26.5 GHz) and measure them to ascertain the influence of material loss on the sharpness of filter transitions.