The antenna of the satellite must be pointed accurately toward the earth station antenna with which the satellite is in communication using a high-gain reflector antenna system. In order to achieve this accurate pointing, satellite antenna commonly employ tracking systems to provide signals indicative of the pointing errors in elevation and azimuth relative to the antenna beam of the earth station antenna. In a tracking system, three signals are used for the pointing accuracy of the satellite antenna. These three tracking signals are the azimuth difference signal, elevation difference signal, and the sum signal. The phase and amplitude characteristics of these three signals are utilized in a conventional manner to generate elevation angle error and azimuth angle error signals to control the pointing direction of the satellite antenna.
Typically, the tracking system on the satellite utilizes a monopulse-tracking configuration in which a plurality of antennas, feeding a reflector system, is employed to develop three tracking signals indicative of the pointing accuracy of the satellite antenna. These three tracking signals are the azimuth difference signal, elevation difference signal, and the sum signal. These signals can be generated by multimode monopulse tracking, e.g., as outlined in [1, 2]. One disadvantage of conventional monopulse tracking systems is that such systems are designed to operate with cumbersome antenna arrays (4 horns are 5 horns) . In such arrays, the plurality of antennas is used to develop the sum and difference signals needed to provide the receiver with the means for developing the elevation and azimuth angle error signals for controlling the tracking system. Such cumbersome plural antenna arrays tend to be larger and heavier than desirable at high frequencies. Depending on the applications, different types of multimode mono pulse techniques are feasible [4-6] but none of these designs operate in dual mode. The presented design of Monopulse multimode tracking feed in this paper eliminates all these issues. The constraints of the requirement of single dual-mode tracking feed with communication channel necessitate the development of this new type multi-mode tracking feed.
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