Spurious Response Suppression in Microstrip Bandpass Filters Using Defected Microstrip Structures

Abstract

A new technique for suppressing the spurious passband of microstrip bandpass filters using defected microstrip structures is presented. This new defected microstrip structure resonator is realized by etching an open ring in the microstrip line. Due to its bandstop nature, the defected microstrip structure resonator can be used in microstrip bandpass filters to eliminate the spurious response. A detailed, fast, and accurate analysis using multiconductor transmission lines, and the method of lines is introduced to design the defected microstrip structure structure. The great advantage of the proposed technique is that the design procedure of the filter does not differ from its conventional counterpart; also, the transmission zeros can be allocated to suppress any unwanted passband. To demonstrate the versatility of the proposed method, simulated and measured results for two typical coupled-line and interdigital bandpass filters are presented. The results reveal that the defected microstrip structure integrated bandpass filters can provide a rejection level exceeding 35 dB in the first spurious passband.