Influence of a lightning rod on the bearing accuracy of a direction finding system

Direction finding systems based on amplitude-comparison algorithms are commonly used today due to their simplicity and robustness. In order to protect the physical structure from lightning strikes, proper lightning protection must be applied. In many cases, due to the complexity of such a system, an internal lightning rod is not feasible. Placed externally, the metal rod influences the antenna patterns and ultimately deteriorates the detection quality of the whole system. In this paper, an analytical model is developed based on the Mie scattering of a perfect conducting cylinder to estimate an affected antenna pattern. Measurements confirm the validity of the analytical model. The impact on the overall bearing error is evaluated for different configurations of the system, and explain the significant errors for practical settings.