Low-sidelobe radar antennas

The advances that made sidelobes of -50 dB possible are recounted, and the factors determining whether the sidelobes can be carried into wider bandwidths are discussed. Attention is also given to the use of sidelobes in agile and active arrays. That slotted arrays were the first to achieve ultra-low sidelobes is not considered an accident. Each point in the distribution is determined individually by slot location and shape, and these can be readily milled with exactness. Also described are corporate-fed planar arrays, reflectors and lenses, and conformal arrays. In discussing tolerance and bandwidth, it is pointed out that for any antenna the key to achieving low sidelobes is to recognize and control the sources of error that degrade sidelobe levels. In general, the error sources are in the structure, mutual coupling, component manufacturing tolerance, and frequency response, and they give rise to errors of three types: gradual distortion, random errors, and systematic errors. Each of these is discussed.