: Problems exist with the measurement of large aperture antennas due to the far field requirement. This paper discusses a new method to measure a phased array at about 1/10 the normal far field. The basic idea involves focusing the test array, at probe, antenna a distance R away from the aperture, and then, measuring an antenna pattern by moving the probe antenna on a constant focal arc given by R cos(Theta). This arc minimizes phase aberrations due to defocusing error. To minimize the amplitude errors, the pattern of the probe antenna is carefully matched in order to compensate for the 1/R variation induced amplitude error. The application of this technique will enable arrays to be measured in anechoic chambers, allowing convenient classified testing, while avoiding the effects of weather, and will reduce the risks inherent in the high power testing on transmit. The results of a computer simulation is presented that characterizes the validity and limitations of the technique.

: The radiation pattern of a curved phased array antenna is distorted when the beam is scanned. This is primarily due to the change of the appearance of the amplitude taper across the aperture which is a consequence of curvature. The approach described in this report, to correct for this phenomenon, is to adjust the aperture taper as a whole, rather than to adjust each individual radiating element separately. If an anti-symmetric taper is added in the proper proportion to a symmetric taper the original taper can be largely recovered. Typically the sum and difference aperture illuminations of an antenna can provide the needed symmetric and anti-symmetric functions. A relatively simple and practical technique of using the sum and difference networks in combination to correct for curvature effects is demonstrated. This technique uses a variable power divider to distribute the power is a prescribed proportion at an arbitrary scan angle to the sum and difference channels. The optimum amount of signal to be distributed to achieve the maximum restoration is found as a function of scan angle and curvature. The analysis is comprehensive, including effects due to the element pattern, antenna size, and the variation of apparent element density. Since attenuators are not used, the method has the added advantage of experiencing no loss of power. The technique can be used to improve any sum and difference illuminations. In this report cosine and sine illumination functions respectively are used.

: This report presents an analysis, design data and preliminary experimental results that demonstrate the use of metal grid angular filters for sidelobe suppression. These results indicate that sidelobe suppression in excess of 30 dB is achievable within 20 deg of the transmission pass band. (Author)