Ultrawideband Circularly Polarized Halved-Type Vivaldi Antenna With Symmetrical Radiation Pattern

In this letter, a novel ultrawideband circularly polarized halved-type Vivaldi antenna (HVA) with symmetrical radiation patterns is presented. As we know, conventional HVAs have the drawback of asymmetricalE-plane radiation patterns and the need for an extra ground plane. To address these issues, a multifunctional HVA element is designed, further constituting a fresh rotational-symmetry structure. In this structure, each HVA element serves as the radiator as well as ground plane for adjacent HVA element, eliminating the need for an extra ground plane. The structure has symmetrical radiation patterns and a compact aperture size of 0.3 × 0.3λ L\!2, whereλLis the wavelength at the lowest operating frequency. A compact sequential phase feeding network is well designed and integrated into the bottom of the structure. Such an example antenna is fabricated and measured. According to the simulated and measured results, the antenna has an ultrawide impedance bandwidth of 111.5% (0.52–1.83 GHz) and a 3 dB axial ratio bandwidth of 100% (0.49–1.47 GHz). Besides, its peak realized gain reaches 7.2 dBic.