Wideband beam forming with a rectangular array antenna

This paper presents a wideband beamformer which avoids the use of frequency filters or delay networks to steer a beam in azimuth over a wide frequency band. To achieve an approximately constant radiation pattern with frequency a rectangular, instead of linear, array of wideband planar monopoles is used. The required weighting coefficients, for signals at individual antenna elements, are real numbers which can be realized by attenuators or amplifiers. For an assumed radiation pattern, these weighting coefficients are determined by neglecting mutual coupling effects between the array elements. The effects of mutual coupling are then studied by performing a full EM analysis of the array. It is shown that mutual coupling degrades the side lobe level in the radiation pattern. To overcome this impairment, the method to compensate this adverse effect is described. The compensated weighting coefficients are determined and the radiation patterns are simulated. The modified weighting coefficients are complex numbers. They can be realized in practice by including quadrature hybrid circuits in addition to attenuators or amplifiers already present in the beamformer