Roundoff algorithms for digital phase shifters that minimize beam shift

Abstract

The performance of a phased array antenna depends upon the phase and amplitude distribution across the aperture. A continuous 13-near phase distribution is required for an efficient focussed beam, but practical phase shifters are digital devices and can only provide an approximation to a linear phase distribution. Consequently some type of roundoff criteria must be established. The method of roundoff affects the radiation pattern characteristics such as beam location and sidelobe level. Accurate target tracking requires that a radar have a small beam pointing error. Low sidelobes are also desirable to prevent jamming and the illumination of clutter. Therefore the goal was to select a roundoff criterion that provides a phase distribution across the aperture to minimize both the beam shift and the sidelobe levels, while simultaneously maximizing the gain. The methods examined are referred to regular roundoff, weighted random roundoff, running sum roundoff and symmetric running sum roundoff. The first two are in common use, but the third and fourth are new methods examined in this paper. It was demonstrated that the latter two have the beam shift of the four roundoff methods, without significantly degrading the other pattern properties.