Linear arrays with variable interelement spacings

Optimum broadside arrays with constant spacings, i.e., Dolph-Tchebycheff arrays, use relatively many elements and are often difficult to realize in practice due to mutual coupling effects. To overcome these disadvantages a variety of arrays with widely and variably spaced elements have been designed using both analog and digital computer techniques. These arrays all have many fewer elements than Dolph-Tchebycheff arrays with the same beamwidth and sidelobe level. One of the arrays designed has 21 elements and is 76 wavelengths long when used as a broadside array. The 3-db beamwidth is 0.74 degree, the sidelobe level -7.4 db. The array has perfect steerability in a 1.8:1 bandwidth with no interelement spacing smaller than one-half wavelength in this band. A Dolph-Tchebycheff array with the same beamwidth and sidelobe level uses 53 elements, and the steerability is not perfect even at a single frequency.