Mitigation of signal biases introduced by controlled reception pattern antennas in a high integrity carrier phase differential GPS system.

摘要

This dissertation characterizes the signal biases seen in Controlled Reception Pattern Antennas (CRPAs) and introduces mitigation schemes for undoing those biases. A CRPA is an array of GPS antennas whose received signals are phased and combined to alter the reception gain pattern of the antenna. It has great benefits in rejecting multipath and RFI. However, CRPAs have not been considered for a carrier phase system before this work, and its exact effect on the received GPS signal measurements has not been studied in depth. Individual antenna elements have some received carrier phase variation according to the incident signal direction. The frequency response of the antennas also introduces a similar variation in the received code phase of the GPS signal. When these antennas are populated in an array, mutual coupling between the elements causes the code and carrier phase patterns to alter for each element. For a high-accuracy high-integrity carrier phase differential GPS system, all such effects on the measured GPS signal are undesirable.; One such system for which CRPAs are being considered is the Joint Precision Approach and Landing System (JPALS). The navy variant of JPALS is called Sea-based JPALS, and its ultimate goal is to facilitate automatic landings of aircraft onto aircraft carriers, even in zero visibility conditions. The aircraft carrier is a very challenging multipath (reflected GPS signals) environment. On top of all this, service must be provided even in the presence of hostile RFI. This makes CRPAs greatly desirable for this program. However, the signal biases introduced by CRPAs must be characterized and removed.; This dissertation presents a characterization of the code and carrier phase biases introduced by CRPA antenna hardware, two distinct mitigation schemes for removing these biases from the CRPA output signal, and an error-bound analysis for CRPA implementation in a high-integrity carrier phase differential system such as JPALS. The results will show that a compensation scheme is required, in addition to some implementation requirements (unit-by-unit calibration data, temperature controlled CRPA), in order to successfully apply CRPAs to JPALS and correctly solve the integer ambiguity problem.