Miniaturisation of antenna arrays for mobile communications

The focus of this paper is the miniaturisation of antenna arrays, to exploit diversity schemes for mobile communications. The main parameter determining the size of an array is the spacing between adjacent radiators, which is usually chosen to be half a wavelength. Reducing the spacing introduces mutual coupling between the elements and, hence, a degradation of the radiation pattern and the gain of the antenna. We combine improved design of the individual radiators with a passive decoupling network to overcome these drawbacks. To make ultimate use of all available degrees of freedom for a given number of radiators, superdirective modes must be taken into consideration, though at the expense of reduced bandwidth and high sensitivity to variations in component values.