Asymmetric dual-mode microstrip square loop resonators and filters

Dual-mode microstrip filters with asymmetric filter characteristic employing two rectangular loops within a single mode microstrip square loop resonator were proposed. Two filter designs with a finite-frequency transmission zero on either side of the passband were demonstrated with EM-simulated and measured results. The positive and negative coupling between two resonant modes of microstrip dual-mode resonator is described depending on the size of the loading element. It has been shown that the location of transmission zero can be easily controlled by simply changing the one of dimensions of the loading element.