Large scale antenna array for GPS bistatic radar

Abstract

GPS passive bistatic radar uses signals transmitted by navigation satellites to perform target detection. This research aims to develop a ground-based receiver that detects the reflected GPS signals from air targets. The main challenge for GPS bistatic radar is the difficulty in detecting the extremely weak power GPS signal reflections from a target since GPS satellites are located at very high altitudes and transmit signals at relatively low power levels. The research in this thesis investigates the minimum power of the reflected GPS signal that can be reliably detected by applying several techniques for enhancing the receiver detection performance. The proposed techniques for GPS bistatic radar target detection model include: using a large scale antenna array at the receiver, applying long coherent integration times for the captured data and non-coherently summing the power returns of targets from multiple satellites or receivers. This detection model requires the radar system to incorporate the signal information from a large number of receiving channels and non-cooperative transmitters to perform air target detection. This research also incorporates additional techniques at the pre-detection stage that are essential for the target detection model. Among these techniques include: direct-path GPS signals acquisition that obtains the Doppler frequency component and C/A code pattern from each satellite, array calibration that realigns the inter-element phase errors and orientation of phased-array receiver using the GPS system, and direct-path signal interference cancellation. The GPS bistatic radar target detection performance was initially investigated using the results produced by computer simulations. Then, a prototype phased-array GPS bistatic radar receiver was built to capture target reflections from an aircraft and investigate the detection performance of the system experimentally. The system was able to successfully detect and locate the position of a nearby aircraft, which demonstrates that the techniques introduced for GPS bistatic radar in this thesis do work in practice. The experimental results also provide a benchmark that can be used to estimate the scale of the receiver required for detecting objects at a greater distance.