Circularly Polarized Patch Antenna With Frequency Reconfiguration

A novel circularly polarized (CP) patch antenna with frequency reconfiguration is presented. The antenna consists of a rectangular patch etched with a rectangular-ring slot. Four pairs of varactor diodes are symmetrically placed along the slot. Two orthogonal resonant modes of the patch antenna are simultaneously excited by a single coaxial probe feed. By varying the capacitance values of the varactor diodes with single DC voltage, the resonant frequencies of the two modes can be simultaneously changed. Moreover, by introducing a specific difference between the length and width of the rectangular-ring slot, good CP performances can be obtained over a broad frequency tuning range. A prototype was fabricated and measured. The measured results indicate that a continuously tunable CP operating frequency from 1.92 to 2.51 GHz and stable broadside radiation patterns can be achieved. The measured efficiency rises from about 47% to about 61% as the operating frequency increases from 1.92 to 2.51 GHz.