Fiber-based Microwave Interferometer monitoring the Delay of Fiber-Optic Antenna Downlinks in Radioastronomic Scenarios

In large radioastronomic facilities, such as the Square Kilometre Array (SKA), where arrays of a great many antennas are connected to the processing station through optical fiber connections, the monitoring of the phase shift (or, equivalently, of the delay) induced to the transmitted signal by each optical link is crucial for the array calibration process. Indeed, these connections typically lie (partially or totally) in environments where climate/environmental agents can change the electromagnetic properties of the cable in a significant measure and in a different fashion between one fiber and the other, and this can therefore have a different impact on the value of phase shift (or delay) of each travelling signal. This paper proposes a simple and low-cost technique based on a microwave interferometer realized on optical fiber to monitor the delay introduced by the optical connections and its variations due to external climate agents.