Frequency-Tunable Waveguide Antenna With Miniaturized Aperture Using a Varactor-Loaded

We propose a frequency-tunable waveguide antenna with a size-reduced aperture. Up to now, waveguide antennas with split-ring resonators have exhibited narrow-frequency band- widths. To expand the operating frequency band, the resonant frequency of a split-ring resonator is tuned by adjusting the ca- pacitance of the gap. A capacitor-loaded split-ring resonator is simulated and experimentally tested to validate its performance, andavaractor-loadedsplit-ring resonatoristheninvestigated.The effective capacitance of the varactor-loaded split-ring resonator is changed by varying the external dc voltage. The tunable frequency range extends from 1.96 to 2.36 GHz (a fractional frequency range of 18.5%). The simulations and experiments yield good results for thereflectioncoefficient,radiationpattern,andgain.Theproposed antenna retains the 70% aperture reduction of previously devel- oped split-ring-resonator-loaded waveguide antennas. Index Terms—Probe, split-ring resonator (SRR), varactor- loaded split-ring resonator (VLSRR), waveguide antenna.