Test Results from a Novel Passive Bistatic GPS Radar Using a Phased Sensor Array

GPS bistatic signals have applications for remote sensing in collecting data such as soil moisture content, surface altitude or wave speed. Prior research using these signals has been limited by the low signal power of the bistatic GPS signals. Leveraging off of a previous effort that used a 15-element array, NAVSYS Corporation has developed an advanced bistatic GPS receiver that uses a 109-element GPS antenna array and digital beam steering to provide gain to increase the ability to detect the weak bistatic GPS signals. The enhanced 109-element array offers 20 dB of gain over previous receivers, which use single element tracking and offers promise of retrieving usable return data from a much higher altitude. In this paper, the design of the digital beam-steering receiver is described and data collected during flight tests with the array are presented. The data was collected with the antenna array installed on a Cessna aircraft. Flights were conducted over terrain and water and the data was recorded for post-test analysis. The results of the flight test show the increase in fidelity and observability of the bistatic GPS signals by using digital beam steering. The digital scanning capability of the receiver also increases the area of coverage over which data can be collected from a single aircraft pass. The enhanced data collected will be of benefit for all remote sensing applications using bistatic GPS signals.