Hybrid receiving station architecture

This document presents a detailed description and analysis of the satellite-based antenna system designed to receive Automatic Dependent Surveillance–Broadcast (ADS-B) signals from aircraft via a satellite-mounted receiver. It focuses on the system architecture, design rationale, and performance evaluation, with particular emphasis on the antenna designs developed for accurate estimation of Time of Arrival (TOA), Frequency of Arrival (FOA), and Angle of Arrival (AOA), essential parameters for multilateration (MLAT) and enhanced multilateration (EMLAT) applications. The proposed designs are validated through use cases and simulation results, demonstrating their potential for robust, scalable air traffic surveillance in remote and oceanic regions. The proposed antenna architecture consists of two main subsystems. The first is the antenna array, comprising multiple radiating elements pointed to the maximum distance aimed to achieve, which is the horizon of the Earth. The second is the feeding network, which can be entirely digital or hybrid and is responsible for beam pointing and shaping. Both subsystems are optimized to maximize the gain-to-distance ratio based on the signal’s radiation angle, from Nadir to the horizon. The radiation pattern has also been designed to minimize nulls, ensuring smooth gain variation across the elevation angle. Once the antenna detects a signal with a sufficient signal-to-noise ratio, it is processed to estimate the Angle of Arrival (AOA) and determine the position of the transmitting aircraft. This document explores various antenna configurations, including different radiating elements and array layouts suitable for satellite integration. These designs vary in component quality, system complexity, and expected sensitivity. Each is evaluated for its ability to detect ADS-B messages under varying conditions. A critical parameter for the antenna system is gain, as it directly affects the achievable signal-to-noise ratio and the number of aircraft detected per beam. Detecting too many aircraft can overload the receiver with ADS-B messages (FRUITs), degrading system performance. Higher directivity reduces beamwidth and limits the number of detected aircraft, but requires a larger antenna, presenting a key trade-off in the system design. Antenna bandwidth also impacts system performance. While a wider bandwidth improves Time of Arrival (TOA) estimation accuracy, it increases noise power at the receiver output, potentially reducing the signal-to-noise ratio (SNR) and Minimum Detectable Signal (MDS). Therefore, a careful trade-off between measurement precision and noise management is required. The document concludes by proposing several antenna systems for the satellite-based ADS-B receiver. According to simulations, the proposed antenna arrays provide the necessary gain to maintain a sufficient signal-to-noise ratio for reliable operation. As outlined in the D3.1 deliverable, the receiver should employ an array antenna with a multichannel coherent receiver capable of Digital Beamforming (DBF) to generate multiple beams and estimate the Angle of Arrival (AOA).