Radiation pattern synthesis of a high gain, circularly polarized rectangular antenna array in the Ka band for CubeSat class satellites

Over the last decade, more than one hundred CubeSats have been launched, and this number will double very soon. However, the increasing number of launched satellites is not yet followed by an improvement in the communication technology they use: to date, the majority of orbiting CubeSats transmits their data using frequencies allocated in the radio amateur service. If this trend does not change in favor of more advanced technologies, this class of satellites will not be considered a viable solution for commercial purposes, and thus relegated to the role of educational tool or technology demonstrator. The transition to higher frequencies, like those in the Ka band, will enable the design of small and directive antennas, and will make faster data rates attainable. In the nanosatellites development, an antenna can be very demanding in terms of mass and real estate; efficient radiators such as horn antennas or parabolic reflectors in most cases are not viable solutions because of their mass and surface requirements. An ideal antenna should be thin, flat, small, light and designed to be mounted on the outer surface of the spacecraft. In this context, a microstrip array antenna is a convenient solution in terms of size, mass, mounting and cost. In this paper we design a circularly polarized antenna array, with uniform polarization over a wider bandwidth with respect to the bandwidth of the basic array element. In the design of the proposed array, many parameters are subject to optimization: specifically, gain and bandwidth shall be maximized, while the axial ratio and insertion losses shall be minimized. These parameters can be optimized at every stage of the design: for the single patch, the subarray, and the final array. In order to identify the best compromise possible between physical parameters and electromagnetic performances, a multi-objective optimization approach will be adopted. Finally, also the excitations of the elements are optimized following a deterministic algorithm which allows to improve the electromagnetic performances of the uniform array. Numerical results of the consecutive optimization steps will be illustrated.