Phase Effects Analysis of Patch Antenna CRPAs for JPALS

The Joint Precision Approach and Landing System (JPALS) is being developed to provide navigation to support aircraft landings for the U.S. military. One variant of this is sea based JPALS, which will be implemented on aircraft carriers. Sea based JPALS will be a dual frequency carrier phase DGPS system. In order to meet strict accuracy, integrity, continuity, and availability goals in the presence of hostile jamming and in a harsh multipath environment, advanced technologies are required. One of those being considered is a controlled reception pattern antenna (CRPA) array with beam steering/adaptive null forming capabilities. However, as with all technologies being considered for sea based JPALS, any possible effect on the carrier phase content of the received signal must be well characterized and/or removed. This is especially true for CRPAs since the mechanism by which CRPAs adjust the reception pattern is through the alteration of phase received in each antenna channel. This paper will present an analysis of phase effects seen in the received phase pattern of individual antenna elements in CRPAs. The magnitude and location of these phase effects seen (in terms of incident signal direction) for individual antenna elements are dependent on the exact configuration of the array, and can be attributed to: 1) phase center movement of individual antenna elements, 2) fringing effects for those antenna elements near the edge of the ground plane, and 3) mutual coupling effects introduced by the other antenna elements. It will be demonstrated that the phase pattern of each antenna in a CRPA differs from element to element. A modeling of the phase pattern as a function of azimuth and elevation of the incident signal will also be presented.