Design and measurement of a portable low-noise aerial

In order to investigate the reduction of aerial noise from a small dish with its mainbeam at a low elevation, a 112cm-diameter circular symmetric paraboloid was mounted with a 45° flat plate. The combination was fed so that when the mainbeam was horizontal the feed spillover was predominantly upward. A Dicke-type radiometer is described with synchronously switched i.f. attenuators and a resolution of 10deg K. This was used to investigate the aerial noise against mainbeam elevation angle at 9.6GHz of the dish plus the 45° plate. The aerial noise temperature showed a broad minimum around 30° elevation as expected. The possibility of trading dish size for cryogenic complexity is discussed.