Design of 2-18 GHz balanced antipodal Vivaldi antennas using substrate-integrated lenses

Conventional balanced antipodal Vivaldi antennas (BAVAs) normally have deep ripple levels in E-plane mainlobe region and significant H-plane beamwidth variation over upper frequency band, which are drawbacks for ultra-wideband (UWB) applications. To overcome these issues, this paper introduces two types of lens configurations in front of BAVA. A gradient-index semi-cylindrical lens and a cylindrical lens are employed to improve ripples depth of E-plane mainlobe and broaden H-plane beamwidth, respectively. Both these lenses and BAVA are integrated on the same substrate and the desired refractive indexes of lenses are realized by a combination of a set of air-filled holes in the substrate. Prototypes of the modified BAVA with lenses (BAVA-Ls) are designed, fabricated and experimentally investigated as well. Measured results show close agreement with simulation. The proposed BAVA-Ls exhibit promising performances such as smaller ripple levels in E-plane mainlobe, wider H-plane beamwidth, higher aperture efficiency, and excellent group delay, while maintaining good bandwidth characteristics over 2-18 GHz.