Ultrawideband monopulse antenna with application as a reflector feed

Abstract

A novel ultrawideband pattern diversity antenna, with sum and difference radiation patterns used in monopulse tracking, is proposed. To achieve pattern diversity, a crescent-shaped radiating element is fed from two sides at an angle close to 90°, by two coaxial feeds. The ground is a corner-shaped cavity. The sum and difference patterns can be obtained by in-phase and out-of-phase excitations of the two coaxial ports. A single-element antenna is first studied to show the operating principle of the design. A modified design with two elements is then proposed and studied through simulations and measurements of a fabricated prototype, showing excellent radiation characteristics over a large frequency bandwidth. The application of this antenna as a reflector feed is then studied. It is shown that the antenna can theoretically feed a prime focus reflector with 60% (for the sum pattern) efficiency over a 48% fractional bandwidth (5.5-9 GHz), with a maximum efficiency of 75%. The antenna is compact (5 × 4.1 × 2 cm3) and has low cost and simple fabrication. To the best of authors' knowledge, this is the first attempt to feed a reflector with this class of antennas.