On the importance of sub-array design in the suppression of undesirable grating lobes

A useful strategy in simplifying the development of large antenna arrays is to use sub-arrays as a building-block. When employing this strategy, care must be taken in designing and implementing the sub-arrays because they can be considered array elements that are more than one wavelength apart resulting in array factor grating lobes. In ideal situations, the grating lobes that one would expect are cancelled out by the individual sub-array pattern nulls. However, if care is not taken in the design of the sub-array, errors in that design can distort the sub-array pattern and cause it to no longer properly cancel the grating lobes and ultimately degrade the overall array pattern. Thus, it is essential to understand the mechanism that can cause unwanted distortion in the sub-array pattern. Here, we investigate a number of situations that can cause unwanted distortions in the sub-array pattern and their effects on the final overall pattern. We will focus on 1×4 sub-arrays, which are one of the more common sub-array designs that are implemented in large arrays. Analysis of the array factor and simple simulations will demonstrate the possible mechanisms of these distortions and illustrate the importance of the sub-array design.