Analysis of Carrier Phase and Group Delay Biases Introduced by CRPA Hardware

The benefits afforded by Controlled Reception Pattern Antennas (CRPAs) in multipath and interference mitigation are well documented, and they find use in many applications today. As such, CRPAs are being considered for use in the Joint Precision Approach and Landing System (JPALS) program. The Navy variant of JPALS, Sea-based JPALS, will be a dual-frequency, carrier phase, differential GPS system whose operational environment is expected to be very harsh in terms of multipath and RFI. For any carrier phase differential GPS system, phase integrity is critical for correct integer ambiguity resolution. In addition, JPALS has extremely stringent navigation performance specifications, and with any technology being considered for JPALS, any potential unwanted effect on the CRPA output signal which may degrade navigation performance must be analyzed. This paper will present an analysis of the signal biases introduced by the CRPA hardware. The effects can be broken down into two major sources: phase delay and group delay. Both of these sources vary according to incident signal direction and the configuration of the adjacent antenna elements. The analysis presented will be for a single frequency patch antenna CRPA designed and constructed at Stanford University. The phase effects of CRPAs have been published in previous work. This paper will present the effects of antenna group delay on the code phase of the received signal. More importantly, this paper will present an analysis of these effects for the CRPA output signal. This analysis will show that CRPAs will introduce biases in both the code and carrier phase of the signal, and depending on what kind of processing algorithm is used for the CRPA, will require some form of mitigation of these effects.