LOW COST, LIGHTWEIGHT, SINGLE AXIS TRACKING SYSTEM FOR UNMANNED VEHICLE APPLICATION

Abstract

Recent events in the Falkland Islands, and in Israel/Lebanon, have made the tactical use of unmanned airborne vehicle systems a practical reality The control of the unmanned vehicles requires a radio uplink, a downlink for vehicle position determination, for telemetering monitored events and functions, and, in some instances, transmission of television or other information. While for some situations the ground antenna can be fixed, the majority of today’s applications require a steerable antenna. This is dictated by the fact that a high gain (and therefore, narrow beam) antenna is required for maximum range, and that for most scenarios, vehicle position must be determined. The increasing use of unmanned vehicles indicates the need for a low-cost tracking antenna system. Use of the tracking antenna in transportable and/or mobile systems calls for a lightweight system. A two-axis antenna, in addition to being heavy, is more than twice the cost of a single-axis tracking antenna system. Slant range of the vehicle is determined by the use of a ranging tone and ground range is determined by comparing altitude data telemetered back from an on-board altimeter with slant range. Complete positional data are obtained given the ground range and the bearing angle from the singleaxis tracking antenna. A microprocessor-based antenna control unit allows all systematic errors of the antenna system to be calibrated out of the angle data. A binomially fed, linearly polarized, folded pillbox horn antenna, having extremely low sidelobes, permits wide angle acquisition, and high elevation angle tracking without introducing bearing angle error. The use of graphite fiber materials for antenna and rotator construction provides savings both in cost and weight. A newly developed lightweight and low-cost single-axis tracking antenna that utilizes all these techniques is described in this paper.