Three-Dimensional Anti-Jamming Array Processing for GNSS-Based Navigational Aid Inspection

Abstract

Global Navigational Satellite System (GNSS) Radio Frequency (RF) links are susceptible to interference. In signal compromised environments, the capability to combat RF interference (such as jamming) is necessary. Techniques and results of applying adaptive anti-jamming beam/null-forming processing to the measured three-dimensional (3D) and two-dimensional (2D) radiation patterns of L1-Band RHCP GNSS antenna arrays are investigated. Also, for reference studies in this thesis and for verification of null-forming methods, an S-Band antenna array is investigated. I developed a small-scale 2 by 3 and 1 by 6 custom arrays along with a 7-element circular array for demonstrating the GPS L1-Band operation. For the S-Band, a pre-built 1 by 8 linear array was used. The visualization of the GPS array pattern through synthesis and direct measurements serves as the basis for algorithm implementations. Individual antenna element measurements are collected first and then, in post-processing, nulling techniques are applied. A digital beamformer generates weighted vectors for each element based on the locations of the multiple interfering signals. The covariance matrix of the interfering signals is utilized. Its inverse is taken and multiplied by the steering vector of the desired signal.

The goal is to optimize the locations and depths of the nulls to suppress the unwanted interference while still having the main beam directed toward the desired signal. Generated beam-forming coefficients are applied through digital post-processing and through an analog phased array controller. The digital and analog methods are compared against each other. The evaluation of these null-forming techniques and measurement processes will be beneficial for the analysis of both civilian and military GNSS-based landing and navigational support systems.