A tunable transmission line based on an SIW loaded by a new single-cell metamaterial

Two substrate integrated waveguides (SIW) loaded by a new single metamaterial (MTM) cell are discussed theoretically and experimentally. The first MTM-loaded SIW shows a passband-like response with balanced backward- and forward-wave passbands below and above the cutoff frequency of the host SIW, respectively. The MTM-SIW structure is then slightly manipulated and two varactor diodes are added to achieve frequency agility. The resulting varactor-loaded transmission line (TL) shows tunable transmission bands whose frequency characteristics can be controlled continuously by varying the reverse bias voltage applied to the varactors. The two MTM-SIW TLs are discussed based on the study of a Composite Right/Left Handed (CRLH) MTM-based SIW considering the dispersion diagrams and the equivalent circuits. Finally, prototypes of the former and the varactor-loaded MTM-SIW TL are fabricated and tested. The measured results are in good agreement with those obtained by the simulation and analysis.