A Miniaturized Wideband Directional Circularly Polarized Antenna Based on Bent Vivaldi Antenna Structure

This letter describes the design of compact broadband circularly polarized (CP) array antenna based on the Vivaldi element. Four sequentially rotated Vivaldi antenna elements are bent into the antenna aperture for miniaturization and are fed by a 1-to-4 integrated feeding network with identical amplitude and orthogonal phase. A coupling metal patch is mounted on the top of the antenna to enhance the impedance, circular polarization, and gain characteristics. A prototype is fabricated and measured for demonstration purposes, the results show a 10dB impedance bandwidth (IBW) of 57.8% (1.6-2.9GHz) and a 3-dB axial ratio bandwidth (ARBW) of 50.7% (1.65-2.77GHz). Furthermore, the antenna has outstanding radiation performance, with a peak gain of 5.6dBic across the entire operating bandwidth. The antenna, in particular, is highly miniaturized in comparison to other similar antennas, with an overall size of 0.26 ${\lambda }_{l}$ × 0.26 ${\lambda }_{l}$ × 0.12 ${\lambda }_{l}$ ( ${\lambda }_{l}$ is the free-space wavelength at 1.6GHz).