Frequency-Tunable Zeroth-Order Resonator Antenna Based on Capacitor-Loaded Coplanar Waveguide

A compact, frequency-tunable zeroth-order resonator (ZOR) antenna designed with capacitor-loaded (CL) coplanar waveguide (CPW) is proposed. By replacing the series capacitors used in the conventional CL CPW ZOR antenna with varactor diodes and properly designing the feed-in capacitor, a well-matched and continuously tunable resonant frequency is acquired. For a satisfactory rf-dc isolation without using bias Tee, a simple dc bias circuit for the varactor diodes is devised. For verification, the proposed antenna is designed, fabricated, and tested, and its performance is compared to other frequencytunable ZOR antennas. Limited by the capacitance tuning range of the varactor diodes at hand, the operating frequency of the prototype antenna is tunable only from 2.54 GHz to 2.78 GHz as the dc bias voltage is changed from 0 to 10 V. Nonetheless, the proposed design has a simple planar structure and a compact size while exhibiting a reasonable gain in between 1.23 and 2.03 dBi.