GNSS constellations monitoring using a multibeam Luneburg lens antenna system.

Global Navigation Satellite Systems (GNSS) are now essential in our modern life: from synchronizing vital infrastructure to accurate navigation. Robust monitoring systems are required to guarantee the dependability and security of satellite constellations as society depends more and more on GNSS for precise positioning, timing, and navigation. This research presents a state-of-the-art GNSS monitoring antenna system capable of a high-performance sensing of all the main constellations.The antenna system is composed of multiple blocks which are modular depending on the needs: a modified Luneburg lens with an associated source array, a filtering stage, an amplification stage, and a receiver stage. Each component can be changed independently from the others allowing easy maintenance and more interestingly, re-configurable antenna specifications. To receive multiple GNSS signals at the same time a custom receiver block has been designed to have 16 RF signal input, each beam created by the antenna is connected to a GNSS receiver which is multi-constellations and dual frequency (GALILEO E1/E5 and GPS L1/L5). All the signals are then logged or observed live.The receivers are connected to a Raspberry Pi which enable the beams of interests using the publicly available satellites ephemerides (using two-line element files).A Luneburg lens, see figure, is a type of spherical lens that has a gradual variation of refractive index from the center to the edge. This property makes it suitable for use in a multi-beam GNSS antenna, as it can focus multiple beams toward different satellite signals simultaneously. The lens shape and refractive index distribution cause the beams from the antenna elements to point at different locations in space, creating multiple high gain beams that can be directed towards different satellites. The lens is modified to accommodate a source array and is 3D printed to have 10 dBi gain at 15° elevation.