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Precise positioning in Global Navigation Satellite System requires the exact location of antenna phase center. Various published methods are quite complex and difficult to execute. A simple but improved technique is systematically analyzed and implemented to determine the mean electrical phase center of horn and patch antenna in Cartesian coordinates. It involves the measurement of relative phase pattern which is post-processed numerically. The phase center variation with change in observation angle and frequency are presented.

Estimation and mitigation of multipath error improves the positional accuracy of GPS. The objective of this paper is to estimate the efiect of multipath interference at the receiver antenna based on both code and carrier phase measurements using Code minus Carrier (CMC) technique, and suggest a suitable method to mitigate it for static applications. Difierent adaptive fllters such as Least Mean Squares (LMS) and various Recursive Least Squares (RLS) are considered to mitigate the error. The estimated multipath error for a typical signal is 0.8m and 2.1m on L1 and L2 carriers, respectively. The results due to adaptive flltering methods are encouraging and signiflcant reduction of error (cm level) is observed. It is found that, when compared with experimental static dual frequency GPS receiver data, LMS and RLS fllters give better error minimization on L1 and L2, respectively.

Local Area Augmentation System (LAAS) based on multi- constellation GNSS can provide improved accuracy, availability and integrity needed to support all weather category II and III precision approach landing of aircraft. In order to receive satellite signals of GNSS, an antenna working over wide frequency band and high phase center stability is preferred. Commonly used antennas like crossed dipoles, patch etc. are inherently narrow band. This paper describes the design and development of half-cardioid shaped dual arm, wide band printed circuit antenna. The antenna has low VSWR of < 3 : 1, a stable phase center and good right hand circularly polarized radiation patterns covering full L-band frequencies. The simulated and measured results compare well. This compact antenna can also be used on ground, ship and airborne platforms to receive signals from multiple GNSS satellites above the horizon.