Band Enhancement in Reflectarrays for Space Communications Based on Multi-Frequency Synthesis Procedure

Abstract

Direct-to-home (DTH) applications usually require a radiation pattern with a given footprint on the surface of the Earth. They also impose stringent cross-polarization requirements in the form of crosspolar discrimination (XPD) or crosspolar isolation in a given bandwidth. This paper describes a multi-frequency wideband optimization procedure and performance results of a very large spaceborne reflectarray for DTH application in a 10% bandwidth. The proposed design methodology is based on the generalized intersection approach and the use of a multi-resonant unit cell with multiple degrees of freedom (DoF). The procedure is divided into three stages to facilitate convergence towards a wideband performance. First, a initial narrowband design at central frequency is obtained. Then, a broadband optimization including XPD requirements is carried out with a limited number of DoF. Finally, more DoF are included in the last stage optimization to obtain a wideband reflectarray with improved cross-polarization performance. A minimum improvement of 4.8 dB is achieved in the cross-polarization performance for both XPD and XPI in a 10% bandwidth, while ensuring that the copolar pattern complies with the specifications in the whole band.