Achievable bandwidth of mu-negative medium made of ring resonators considering losses

This paper presents some guidelines to achieve wide bandwidth and low loss in the design of mu-negative medium consisting of SRR-type resonators through a structural change from an engineering point of view. The effective permeability for the single ring resonator (RR) medium is expressed in a very convenient form to facilitate the analysis of the bandwidth and losses by introducing appropriate structural reduction factors. With the optimization of these factors, the maximum achievable mu-negative bandwidth has been found to be approximately 25 %, irrespective of resonant frequencies. When the unit cell size is one tenth of wavelength and ring-type loops are used, it has been found that the imaginary part of the effective permeability (or loss tangent) in case its real part is -1 could be 0.0008, 0.008, and 0.08, for the resonant frequency of 100 MHz, 10 GHz, and 1 THz, respectively. The loss tangent for the planar-type loop case is somewhat larger than that for the ring-type case.