Monolithic active array limitations due to substrate modes

Monolithic integration of antenna elements, with other passive and active components on a gallium arsenide wafer, to form a phased array antenna assembly has been visualised, in terms of cost-effective performance, as an ideal product for exploiting the millimetre-wave spectrum. In its simplest form it is assumed that the planar array is on one face of the wafer and that the reverse side is a metallised ground plane and heat sink. The design challenge is to accommodate all of the functions to be performed by the array of elements within an area of wafer necessary for the required, antenna directivity. This simple structure appears to be compatible with monolithic technology and with antenna operation that involves electric current type radiating elements in front of a highly conducting reflecting surface. A wafer thickness of about one quarter of the wavelength in the dielectric is indicated and, to avoid grating lobes with a uniform array, an element-to-element spacing of one-half of a free space wavelength is indicated. The required directivity determines the number of elements, the antenna array aperture and the area of wafer needed.