High Fidelity Antenna Model Validation Results of a GNSS Multipath Limiting Antenna

The local area augmentation system (LAAS) is a proposed satellite-based landing system by the Federal Aviation Administration (FAA) to serve as a navigation aid for commercial aircraft during the approach and landing phase of flight. The LAAS utilizes a special ground-based antenna array called the multipath limiting antenna (MLA) to provide differentially corrected global navigation satellite system (GNSS) data to oncoming aircraft as well as to reduce the largest error contributor to pseudo-range estimates; the ground multipath. The performance of the MLA is characterized in terms of its desired-to-undesired (D/U) gain ratio, phase center variation (PCV) and group delay (GD). A high fidelity antenna model (HFAM) of the MLA is presented that estimates the D/U, PCV, and GD as a function of elevation angle. The model consists of two main components: (1) a microwave feed distribution circuit model created using a circuit simulator, and (2) a radiating structure model developed using a full-wave method of moments (MoM) field solver. The performance of the model was assessed against antenna range measurements. The results of the HFAM show good correlation for the D/U and PCV while a significant bias was observed on the results for the GD. The dependence of the GD on the radiating element's impedance, tuning process, and Doppler frequency shift are demonstrated via simulations.