Abstract
In this paper, metamaterial loading on loop and open loop microstrip filters is investigated where both rectangular loop and open loop structures are considered. Spiral resonators are loaded on the four sides of the square loop and result in higher size reduction compared to the conventional split ring resonators with identical structural parameters. It is shown that, for both proposed filters, metamaterial loading provides size reduction, due to possessing lower resonant frequency of spiral resonators. The structures are analytically investigated through the transmission matrix method. In the designed rectangular loop filters, there are two nulls on both sides of the pass-band, which provide high out-of-band rejection and is preserved in the corresponding miniaturized metamaterial loaded structures. However open loop resonators provide lower resonant frequencies or more compact size filters. The proposed filter is fabricated and tested and measured results are in good agreement with simulation ones.