Optimum elevation angle estimation in the presence of ground reflection multipath

Radars that are developed for the purpose of monitoring aircraft landings in the terminal Air Traffic Control system can be designed to exploit the relatively high signal-to-noise ratio that characterizes the power budgets calculated for such a link. An interferometer using a pair of low gain antennas can be used to obtain passive coverage over a large azimuth and elevation sector. A large base line can be used to obtain the desired elevation angle estimation accuracy. An optimal tradeoff between the width of the subarray aperture and the width of the interferometer base line is performed that achieves a specified elevation angle estimation error while minimizing the overall height of the interferometer configuration. The algorithm searches through the class of antenna patterns that can be synthesized from so-called finite impulse, linear phase digital filters. In Part II, the design of a separate sensor for resolving the interferometer ambiguities is formulated as a hypothesis testing problem and solved using statistical decision theory. A bound on the probability of an ambiguity error is derived that accounts for the effects of ground reflection multipath and receiver noise. Acceptable performance can be achieved using a 4-element non-uniformly spaced array (0, 3.2, 6.4, 11.2 wavelengths) with relatively inexpensive dipole antennas mounted on tri-plane reflectors.