Indian Journal of Science and Technology

Abstract

Marine radars are used to measure the bearing and distance of ships, to navigate and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships. The asymmetrical sum patterns are very useful for marine radars when the ships sail in turbulent waters, the ships are subject to roll and pitch. Under these circumstances the communication is disturbed and sometimes it totally fails. In the applications, where the main beam is to point in desired direction and the sidelobes are to be suppressed to the desirable extent to reduce the ground clutter, the sum patterns with symmetric sidelobes are not suitable. The modified Elliott pattern is an excellent low-sidelobe distribution and has good efficiency. The modified Elliott pattern is itself a convenient illumination, that it can produce asymmetric patterns on both sides of the main beam. In the present work suitable amplitude and phase distributions are derived by using Fourier Transform technique to produce asymmetrical sum patterns. The weights of the each element are estimated at the source position. The source positions are found out according to Ishimuru spacing. These patterns are computed for small and large arrays. These patterns are useful in high resolution radars in point to point communication and also used in the marine radars.

Keywords: Asymmetric Sum Pattern, Ishimaru Spacing, Modified Elliott Pattern, Marine Radar Applications