Compact bandpass ring resonator filter with enhanced wide-band rejection characteristics using defected ground structures

This letter addresses a modified bandpass ring resonator filter providing compact size, low insertion-loss, wide bandwidth, sharp rejection, and suppressed higher order modes. It is demonstrated that the use of internal folded stubs translates into an overall size reduction of more than 70% through the exploitation of the internal ring area. The introduction of defected ground structures enhances the rejection of higher order modes beside offering a further advantage in terms of size reduction. It is furthermore shown that electromagnetic simulations, transmission line model, as well as measurement results are in very good agreement.