Random sparse arrays Preliminary 1.0 Random Sparse Arrays: An option for SKAI?

One of the major challenges in the design of SKAI is the required ultra-wide frequency bandwidth. The decade of bandwidth could be split up into several frequency regions. For each region a separate radiator could be used with an element distance smaller than λ/2 in order to avoid grating lobes. The main disadvantages of this concept are the complexity (costs) and mutual coupling between the various radiating elements. A more attractive option for SKAI (from a cost and complexity point of view) is the use of ultra wideband elements that cover a decade of bandwidth. These elements could be placed at λ/2 at the lowest frequency. As a result, the element spacing would by equal to 5λ at the highest frequency. An antenna element in this array could be a log-periodic antenna, a bunny-ear antenna or a Vivaldi type of radiator. The disadvantage of this so-called sparse-array concept is the appearance of grating lobes at the higher frequencies and the fact that the effective area decreases as λ with increasing frequency. 2