THE SYNTHESIS OF SHAPED PATTERNS WITH FOURIER SERIES TECHNIQUE

In air-surveillance radars, it is required to achieve more uniform signal strength at the input of the receiver as a target moves with a constant height within the beam. The cosecant squared patterns are designed for this. A pattern synthesis method for a linear array which produces a desired radiation pattern is obtained by using the integral mean of its Fourier approximation. The Fourier series method is usually applied to the synthesis of shaped-beam patterns that are wide compared to the minimum array beam width.

Fourier series method has been proposed for optimizing element excitations in linear phased arrays for synthesizing a cosecant-squared pattern. The Fourier series synthesized pattern gives very sharp roll off from the main beam to the side-lobe region; that is, small transition width. According to this method, the properties of a realized pattern can be easily controlled by the number of elements, the beam width and the element spacing, and the weight function to the Fourier coefficient function. This method provides the least mean squared error approximation of the desired pattern for d ≥ 0.5λ. If the spacing is closer, the domain of integration exceeds the visible region and the definition of the pattern is not unique. For a specified beam shape, Cosecant beams of different widths are generated by using Fourier series method. They are presented in u domain (Sin θ). By using Matlab software the patterns are evaluated.