The effects of an ionospherically induced partially coherent wavefront on the performance of a thinned random antenna array

Very large aperture antenna arrays are being planned for future military applications. It is known that due to irregularities in the ionosphere, where the reflection process takes place, the wavefront across such apertures becomes less coherent as the aperture size is increased. The main thrust of this study is to examine the degradation in the antenna gain and pattern characteristics of a thinned linear array, with 100 elements randomly spaced with a Hamming spatial taper, over a baseline of 10 km, for frequencies from 6 to 30 MHz. These results are then compared with those for a filled linear array having 400 Hamming amplitude-weighted elements and a baseline of 10 km. It is found that the effects of a partially coherent wavefront on the thinned array are comparable to those for the filled array in that the loss in gain and main-beam broadening are similar