Jammer Tracking with Frequency-scanned Radars by Lobe Comparison

Frequency-scanned array radars may be preferred to phase-scanned radars because they tend to be cheaper and simpler. When conventional frequency-scanned radars are used to measure the angular position of jammers, however, large errors can result. These can be eliminate with the lobe-comparison technique. The response of a frequency-scanned array to a jammer can be compared with that of a filter whose characteristics depend on the angle of signal arrival. Variations of jammer power with frequency »nd time can distort the array output spectrum to cause measurement errors. With lobe comparison, the array is divided to produce two slightly different frequency response functions (equivalent to two beams, like those in a monopulse radar). The angle of signal arrival is estimated by comparing the response of the two arrays in a narrow frequency band. If the band is sufficiently narrow, measurement error can be reduced to a satisfactory level with no penalty in noise performance. In practice, a bandwidth about one-fifth that of the radar signal reduces error to less than the usual fixed-error limit of the array. Lobe comparison can be applied to frequency-scanned radars, including phase-frequency-scanned arrays, with only a small increase, in cost and complexity. The improved performance in measuring jammer angular position compares well with that of phase-scanned arrays.