Tunable dual-frequency immittance inverters on dual-composite right/left-handed transmission line

Advanced lumped-element immittance inverters supporting dual-frequency operation and tunability of operational frequencies are the key enablers to design small-size tunable dual-bandpass filters. The paper presents a design concept of tunable dual-frequency immittance inverters based on the dual-composite right/left-handed transmission line (D-CRLH TL) unit cells with variable capacitors. Tunability of such an immittance inverter is limited by a tolerable variation of the inverter parameter which changes when tuning the operational frequencies. At least ±10% tuning of the both operational frequencies is shown feasible theoretically and experimentally.