Multibeam reflectarray for transmit satellite antennas in Ka band using beam-squint

This contribution describes a design concept based on beam squint effect in printed reflectarrays that allows to produce multiple contiguous beams at 19.5 and 20 GHz, by discriminating in frequency. A 1.6-m reflectarray has been proposed to produce 10 beams separated 0.5 degree using five feeds with frequency reuse. The simulated radiation patterns show a peak gain better than 47.6 dBi, with side-lobe levels close to -22 dB. The proposed concept can be suitable for multiple spot beam satellites in Ka-band.

I. Introduction

A reflectarray antenna is composed of a planar array of printed elements on a dielectric sheet over a ground plane. The phase of the reflected field on each element can be adjusted to produce a focused or a shaped beam (usually by varying the dimensions of the printed elements) when the antenna is illuminated by a feed [1]. The effect of beam-squint in reflectarray antennas implies that beam direction changes with frequency. This phenomenon has been previously studied by other authors [2], proving that it is mainly caused by a shifting of the focal point at off-center frequencies, rather than other factors, such as the type of reflectarray element or the lattice size used. Furthermore, some methods have been already proposed to reduce or suppress it [3] [4]. In this paper, the authors present a preliminary design of a printed reflectarray antenna to generate multiple closely separated beams with frequency reuse (f1= 19.5 GHz and f2= 20.0 GHz), using beam squint to achieve discrimination in frequency. The selected frequencies are in the allocated band for transmission in Ka-band multi-spot beam satellites. The proposed concept will allow a reduction in the number of feeds needed to provide the multi-spot coverage.