Novel Compact Microstrip Square Ring Bandpass Filters

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Abstract
Three types of novel microstrip bandpass filters, a square split ring stepped-impedance bandpass filter, a square ring stepped-impedance bandpass filter, and a dual-mode square ring bandpass filter, which operate from L to S waveband are proposed, their filter performances are calculated. In these novel structures, ring stepped-impedance resonator, DGS and dual-mode technique are applied to not only reduce the volume but also improve the frequency responses of filters. The optimized results show that microstrip bandpass filter with DGS has nicer performances such as low insertion losses, wide stopband responses etc., while with dual-mode technique, a pair of transmission zeros can be implemented and the filter performances are effectively improved. The filters proposed in this paper have outstanding advantages such as compact and novel structures, small volumes, high selectivity, wide stopband responses, low insertion losses and so on, and can be applied in wearable systems.