"Lost beams" from a dielectric covered phased-array aperture

Considerable attention has been devoted to the anomalies in the radiation pattern of a phased-array antenna aperture covered with a dielectric sheet. This phenomenon appears as a notch in the element radiation pattern at a scan angle smaller than that commensurate with the appearance of the grating lobes in real space. This communication discusses the observation of this phenomenon in a 96-element phased array of triangularspaced waveguide radiators utilizing a dielectric impedance matching transformer on the radiating aperture. The effect of the dielectric sheet on the aperture was observed both as a deep notch in the radiation pattern of the central element (with the remaining 95 elements terminated) and in "lost beams" as the 96-element phased-array beam was steered to the angles corresponding to the element pattern nulls. Further, these data are in good agreement with reflection coefficient maxima measured in waveguide array simulators.