Optimum tilt angles and beam steering characteristics of phased array radar systems

Abstract

For radar systems, phased array antenna involves many design options. Often, the most important parameters in optimizing the design are cost and weight. In phased array antennas, the number of radiator rows is one of the important factors to minimizing both cost and weight. This is so because cost and weight are directly proportional to the number of radiator rows. Therefore, the choice of antenna tilt angles having relation with element spacing are important design parameters in the radar system design. The optimum tilt angles for several types of uniformly and nonuniformly excited linear arrays are investigated theoretically. Four types of uniform and nonuniform linear arrays are considered, namely, arrays of isotropic elements, of collinear short dipoles, and of parallel short dipoles, and broadside array of dipole crosses. As a nonuniformly excited array case, directivities of Chebyshev array factors are computed to obtain the optimum tilt angle. Next, the exact directivity including phase shift factors for several types of uniformly excited planar arrays is obtained. The approximate directivity calculations are compared with the exact results. Curves of directivity versus interelement spacing and scan angle for planar arrays with these element power patterns are also presented. The optimum tilt angles for several types of dipole planar arrays are obtained. We propose two critera to determine the optimum tilt angles for planar antenna arrays. One is maximizing the directivity in the azimuth direction at the horizon and the other is maximizing the lowest directivity in the azimuth direction. Lastly, the beam steering commands (such as the phase and frequency commands) for a desired beam position in the rotating phase and frequency scan radar (RPFSR) system are derived in terms of the ground based coordinate system. In general, the antenna coordinate system does not coincide with a ground based (or earth fixed) coordinate system. Because the normal of the...