An Ultrawideband Circularly-Polarized Vivaldi Antenna With High Gain

This paper proposes a novel ultrawideband antenna with high gain and circular polarization. Its circular polarization can be easily changed to right-handed or left-handed. The antenna consists of four sophisticated antipodal Vivaldi antennas and an ultrawideband feeding network. The feeding network composes of four horizontal-to-vertical transitions, a two-to-four power divider, and a 3-dB directional coupler. This network can provide two pairs of outputs with equal magnitude and ninety-degree phase difference. In addition, it is horizontally fed with a single input port that can be directly connected to the corresponding circuit board. The newly introduced transition can reduce the discontinuity between the horizontally placed circuit and vertically standing antenna. A prototype antenna is designed, fabricated, and tested. Its impedance-matching, circularly-polarized and stable-gain band is sufficiently wide to cover the entire Ku, K, and Ka bands. The fractional bandwidth (FBW) is as large as 113.2%. In the entire band, the antenna axial ratio is well below 3 dB, while the antenna gain is stable up to 18.35 dBic. Remarkable performance has been achieved in the literature for the first time.