Achieving a Large Gain-Bandwidth Product From a Compact Antenna

Abstract

This paper presents a method to achieve high gain (>20 dBi) and wide bandwidth (>55%) from a compact antenna that is less than one wavelength tall and only $2.6\lambda _{0}$ in diameter at the lowest operating frequency. The antenna comprises of an optimized single-layer superstrate, made out of four dielectric sections, and a ground plane, which are separated by an air cavity. The permittivity and thickness of the dielectric sections decrease in the transverse direction. Two-step optimization method was implemented employing a customized full-wave optimizer to optimize the width and thickness of each dielectric section in the superstrate, while maintaining a fixed overall diameter of the antenna. This optimization results in an antenna with a high gain and a large 3-dB gain bandwidth, without compromising on antenna footprint. A prototype of the new antenna having a superstrate with stepped thickness was fabricated and tested. It exhibits a measured peak broadside directivity and a peak realized gain of 20.7 and 20.2 dBi, respectively. Its measured gain-bandwidth product of 5969 and directivity-bandwidth product (DBP) of 6580 are almost three times the best figures for resonant cavity antennas (RCAs). The total area of the new antenna prototype is $5.3\lambda _{0}^{2}$ and its overall height is $0.89\lambda _{0}$ at the lowest operating frequency. It is significantly more compact and its DBP per unit area and aperture efficiency are significantly greater than those of lens-based antennas. Its measured 3-dB gain bandwidth of 57% is unprecedented for high-gain short antennas, including RCAs. Moreover, over the entire bandwidth, sidelobe levels of the antenna are around −12 and −21 dB in the E- and H-planes, respectively.