Frequency‐tunable circularly polarized twin dual folded inverted‐L antenna with varactor‐loaded split‐ring resonator structures

Abstract

SummaryThe design of a miniaturized frequency‐tunable circularly polarized twin dual folded inverted‐L antenna with varactor‐loaded split‐sing resonator structure is proposed in the paper. The design integrates two linearly polarized inverted‐L antenna elements with double‐folded arms and with a split‐ring resonator (SRR) structures on both sides. To improve the impedance matching and radiation characteristics the double‐folded structure plays a significant role. Although the use of SRRs to the dual inverted‐L antenna elements achieves compact volume, the antenna's radiation efficiency rapidly decreases around the SRR's resonant frequency. The decrease is avoided by employing a variable capacitance diode loaded on both SRR structures (dual folded inverted‐L antenna, VLSRR). The antenna structure is minimized to be about 66 mm in length, 10 mm width, and 1 mm in height (66 × 10 × 1 mm3). The configuration is simplified by using wave feeding. The better values are obtained between the theoretical calculations and simulated results, which validate the design concept and have a wide varactor tuning bandwidth. The simulated and measured results show that the proposed antennas resonate at multiband frequencies: Band 1 (3.28–3.70 GHz) with varactor tuning of 425 MHz; Band 2 (6.42–6.75GHz) with varactor tuning of 331 MHz; and Band 3 (13.75–14.21 GHz) with varactor tuning of 463 MHz, with the impedance bandwidth of 6%, VSWR < 2, and 3‐dB axial ratio (AR) < 3 across the entire operating bands.