Interferometer phasing problems at microwave frequencies

The electric field distribution required to realize a desired radiation pattern is sometimes quickly visualized by means of a transfer function (the spectral sensitivity function) which measures the response of the antenna system to the spatial frequencies of a two-dimensional distribution of brightness. The effects of amplitude and phase errors of individual elements on the directivity and side radiation pattern of an interferometer system are discussed. In the case of phase-switched interferometers it is also important to evaluate the effect of fixed phase error of the switch and feeder system, and phase throw error of the switch, on the radiation pattern. It is shown that these phase errors affect the shape of the radiation pattern only if there exists an odd component in the two-dimensional electric field distribution over an aperture. Details of construction of the transmission line system of a cross-antenna built at Stanford for operation at 9 cm. wavelength are described. The antenna has 16 paraboloidal reflectors in each arm of the cross and provides a pencil beam of nearly 4 minutes of arc width. The experimental technique employed in adjusting amplitude and phase of the field, impressed on each element of the interferometer is also described.