Design of large aperture antenna arrays for a geo-space multi-static radar in Peru
The new requirements in radar and radio astronomy have leveraged antenna array technologies to develop the next generation of instruments and observation techniques. In the low-frequency range, radio observatories such as LWA, LOFAR, and SKA-LOW have involved the design of large-aperture arrays (stations) composed of hundreds of elements, resulting in highly directive systems with electronic beam steering capabilities. However, to meet the expected performance, optimization of several parameters during the design phase is required, as costs and system complexity increase with the number of elements.
In this work, we present the design of two antenna arrays that will be part of a frequency-agile multistatic radio system for geo-space imaging. Each of these arrays, comprising 256 antennas, will be installed in two cities in Peru (Lima and Huancayo). Alongside the Jicamarca Radio Observatory (JRO) radar, these arrays will serve as reception stations for a multistatic radar system to be used for ionospheric studies.
The objective is to identify the optimal configuration for the elements of both arrays. Firstly, a mathematical model for the antenna arrays is introduced, considering the requirements for scientific objectives as well as any constraints. Subsequently, various techniques for sparse array design are explored, primarily relying on deterministic methods (such as Kogan), stochastic approaches (Simulated Annealing), and convex optimization algorithms. The aim is to compare their solutions with the desired performance of the array. The analysis focuses on obtaining a globally optimal solution, surpassing local optima, thus evaluating different cost functions and initial conditions. For instance, an average peak-to-side-lobe level (PSLL) of -28 dB was achieved with cosine-type elements (inverted V antennas) for a 100-meter diameter available area. Finally, since the arrays are expected to operate within the 10-88 MHz range for radio astronomy purposes, the stability of the solution was verified for specific frequencies and steering angles.