Antenna arrays and the devices, components and techniques, which have evolved to implement them, form a very large subdivision of the antenna literature. In Chap. 5, we provide merely a summary of those aspects of the technology that are appropriate to solar power generation and in particular to satellite-based systems as discussed in Chap. 9. Fortunately, the essence of array behaviour can be deduced by examining linear arrays of isotropic radiators, since planar arrays, which are more difficult to analyse directly, can largely be viewed as combinations of linear arrays. The majority of the chapter is engaged in developing and using well-established polynomial techniques which now underpin array analysis and synthesis procedures. Array radiation patterns and their dependence on element numbers and element spacing are discussed mainly with reference to pattern directivity, pattern gain, beamwidth, sidelobes and grating lobes. The optimising of element spacings to maximise gain with the fewest number of possible elements is considered as a precursor to a brief consideration of synthesising arrays to procure specified sidelobe behaviours. Of course, commercial array simulation and design software are readily available to do this on the Internet. Such modelling tools generally employ some form of synthesis procedure, of which there are many as is outline in this chapter.