Design of Wideband Circularly Polarized Vivaldi Antenna with Stable Radiation Pattern

This paper presents a wideband circularly polarized (CP) antenna based on two Vivaldi antenna elements. The two elements are orthogonally placed for compact consideration, and are driven by a specially designed wideband feeding network that splits the input signal into two-way signals with equal magnitude and orthogonal phase. In order to avoid crossing of the feeding lines of two Vivaldi elements, a small shift between them is introduced. This, however, will result in the undesired phase difference of two Vivaldi elements inevitably. To compensate the phase difference and ensure a wide axial ratio bandwidth, the feeding network is specially designed. Besides, to make full use of the antenna space, the feeding network is placed on the surface of two Vivaldi elements. For demonstration purpose, a prototype is fabricated. The measured results show a-10 dB impedance bandwidth of 101.3% (2.35 to 7.18 GHz) and 3 dB axial-ratio bandwidth of 118.4% (2.05 to 8 GHz), and the maximum realized gain is 7.5 dBic. Meanwhile, stable radiation patterns are achieved with the cross-polarization lower than —20 dB across the wide operating bandwidth at boresight direction.