Novel low-impedance microstrip structures for miniaturized microstrip quarter-wave stepped-impedance resonator filters

In this paper, two novel microstrip quarter-wave SIR structures have been proposed. Inserting signal and ground strips in the microstrip line provides another method to lower the characteristic impedance. This approach applies to the low-impedance section of the SIR to decrease the impedance ratio significantly. We have designed and fabricated four four-pole cross-coupled filters with these two structures. A pair of transmission zeros are introduced to obtain higher selectivity by a cross-coupling microstrip. It has been shown that the proposed filters have much more compact size and wider stopband.