TABLE OF CONTENTS The angle of arrival (AOA) approach to distance measurement and location is probably the oldest method and easiest to understand and to implement. All that's needed is a directional antenna. AOA methods are the core of direction finding (DF), which has been used for years to locate illegal transmitters, both broadcast and those used for eavesdropping, and for tracking wild animals that are tagged with tiny transmitters. Generally, AOA is not restricted by the problems dictating conditions of use of other location methods. It requires no cooperation from the target, and any type of signal can be used, including CW. It also is used over wide frequency bands and ranges from HF through microwave and from direct true line-of-sight to long communications distances propagated through the ionosphere.
AOA is a principle component in a radar system. Using radar, only one fixed station is required to determine the location of a target in two or three dimensions. The two methods of AOA and TOF are employed. When using AOA alone, at least two fixed terminals are required, or two separate measurements by a single terminal in motion.
Location and distance are found in an AOA system by triangulation. An example is shown in Figure 8.1. Two base stations are located on the x-axis of a global coordinate system, separated by a distance D. The angles of arrival at the two base stations are ? 1 and ? 2. From trigonometry we find the coordinates of...
