Compact printed microwave filters for wireless communication applications

A novel coupled-line-free wideband bandpass/bandstop filter configuration is designed and tested. The filter is based on a reentrant structure with unequal dielectric constants for the internal and external fillings. As a result, additional symmetrical transmission zeros are generated in the lower and upper stop bands of the bandpass filter; this leads to an elliptic function response and improvement of the pass band and selectivity. Similar conclusions are made about the bandstop filter in terms of the return loss. The general TEM circuit model, in terms of the two-port series connection, is presented for the proposed filters, and then, it is used to determine its electrical parameters. The experimental prototype was fabricated using conventional printed circuit board technology. The measured S-parameters show acceptable agreement with the analytical and full-wave simulations, showing promising potential for different applications.