Measurements, Estimations and Calibration with a Fully Digital Array

Abstract: In modern digital communication, transmission and reception of information through electromagnetic signals requires digital devices that can process high data rates accurately despite being located in information heavy environments. One type of antenna receiver is the digital antenna array, which can steer its lobes electronically to increase or decrease sensitivity in specific directions. A rather recently developed system is the Wideband Digital Array Receiver, developed at Saab Surveillance in Järfälla and referred to as WiDAR. The implementations and possibilities of WiDAR are broad, but no matter its future applications, calibration is an essential feature to ensure truthful reception of data. Any type of electronic system risks errors due to hardware imperfections. The aim of this thesis is to explore and reduce these errors. Measurements with WiDAR were performed in a manner such that some of the intercepted signals were transmitted from a far away located FM and TV-mast. The data was then used to retrieve weights by calculating their relative transfer function, which were applied to calibrate all channels in the antenna array towards a chosen reference channel. These weights could then be on any accumulated set of data measured by WiDAR with hopes to compensate errors in both phase and magnitude. The results show that reducing errors this way was possible, working slightly better when calibrating phase than calibrating magnitude. If more advanced calibration is deemed necessary, further measurements could be performed to investigate where errors or variations occur by isolating different parts of the system. The calibration method used could be further developed by adding an online calibration procedure, meaning relative transfer functions are calculated in real time when performing measurements.