Comparative Analysis Via Simulation of Two Null-Steering Approaches for the Multipath Limiting Antenna for LAAS

M.S. Sharawi and D.N. Aloi

Abstract:	The multipath limiting antenna (MLA) is a proposed component in the Local Area Augmentation System (LAAS) ground architecture that was designed to mitigate ground multipath by creating a radiation pattern that exhibit a desired-to-undesired (D/U) gain ratio greater than 30 dB from horizon up to 35o. The main design driver for this antenna was for LAAS to meet Category I accuracy requirements. Radio frequency interference (RFI), both intentional and/or unintentional, poses significant threats for LAAS to meet Category II/III availability requirements. This threat can be minimized by increasing the satellite signal transmitting power, creating additional civil frequencies, and by developing null-steering antenna technologies. This paper investigates two distinct approaches of incorporating nullsteering capability into the MLA. The vector weighting method (VW) adjusts the feed excitation values of the MLA to reflect the creation of a null in the RFI direction. The beam subtraction method (BS) is utilized by steering a planar array beam into the RFI and then subtracting this beam from the original MLA pattern creating a null in the interference direction. The former suffers from a null that spans the whole azimuth direction affecting the desired signal coming along the same azimuth direction, reducing the availability of satellites. The latter creates a much narrower null in azimuth, but needs an extra antenna array, depends on the polarization of the elements, and sensitive to the subtraction method performed. The effect of these factors along with implementation issues is discussed. The performance of both approaches for L1 is quantified by the null depth, null width, PCV, GD and D/U for an RFI at a specified elevation/azimuth direction by assessing these parameters at the radiation pattern level.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	935 - 948
Cite this article:	Sharawi, M.S., Aloi, D.N., "Comparative Analysis Via Simulation of Two Null-Steering Approaches for the Multipath Limiting Antenna for LAAS," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 935-948.
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