Computer study of dual reflector limited scan antennas

Microwave antennas with limited electronic scanning capability have found increasing use in various radar applications. Major areas include GCA [1], [2], instrumentation radars [3], hostile weapon locators [4] and satellite communications. The primary advantage for the application of these antennas is the lower hardware cost. A particular type of limited scan antenna makes use of a dual reflector configuration which is fed by a small phased array [5], [6]. There are a number of advantages associated with the dual reflector limited scan antennas, in comparison to the single reflector limited scan antennas [7]. Antenna capabilities and hardware limitations of both antenna types will be discussed. Due to the large set of antenna parameters involved in the dual reflector hybrid antenna configurations, computer simulation techniques are used to analyze these antennas. Ray tracing technique is used to determine various gross geometric relationships and diffraction integral technique is used to evaluate the radiation pattern characteristics of a given antenna configuration. The combination of these techniques has been found to be an efficient tool for studying these limited scan antennas. Thus thru the ray tracing program, a set of visual presentations can be obtained to aid the design of various antenna components. Once the antenna geometry is selected, the ray tracing program can also be used to generate the antenna aperture amplitudes and phases, from which the far field pattern can be calculated. More rigorously, the far field pattern can also be obtained by a consecutive set of diffraction integrations. It has been found that these two computations agree very well within the main beam region.