Dual mode zeroth order ring resonator with tuning capability and selective mode excitation

A novel ring configuration supporting two orthogonal unique zeroth order modes is presented. The analysis and the design of this ring are based on the artificially engineered composite right left handed (CRLH) transmission lines. A CRLH transmission line exhibits unusual and more diverse propagation characteristics. In the dispersion diagram a lower left hand (LH) and a higher right hand (RH) frequency range is separated by a propagation band gap. This band gap is confined by two zero phase origins (β=0), associated with an infinite guided wavelength at non-zero frequencies. Using the CRLH-TL in a ring configuration with connected ends, both zero phase origins along with their corresponding frequencies form a valid resonance mode. One zeroth order mode comes with a constant transmission line voltage, a so-called voltage mode, while the transmission line current is zero. The other zeroth order mode is referred to as current mode and operates at resonance with a constant transmission line current and zero voltage along the resonator line. A simple tuning technique for the voltage mode´s resonance frequency is addressed. Different feeding strategies to excite both zeroth order modes simultaneously in a one port device as well as decoupled two port selective mode feeding (either voltage or current mode) are discussed.