We discuss 18.5 GHz attenuation measurements on a 6.4 km path within the Holmdel rain gauge network. The period of measurement includes the summer of 1967 during which many very heavy showers occurred. We examine the data for individual storms separately. There is a marked variability. For example, one shower shows strong evidence of an updraft. The composite results show that γ = 0.041 Σi diRi1.04 where γ is the attenuation per unit length, Ri is the rainfall rate in millimeters per hour measured at the ith rain gauge on the path, and di is the distance in kilometers over which the rain rate Ri applies. When examined in detail, this relationship is satisfactory for attenuations < 3 dB per kilometer; however, the higher attenuations exceed this prediction and agree with the relationship γ = 0.055
The conical horn‐reflector antenna was selected for the satellite communication ground station because of its broadband and low‐noise properties. Prior to the construction of the full‐size antenna, theoretical and model studies of its electrical characteristics were undertaken. These studies consisted of computing gain and radiation patterns for two modes of excitation, constructing of model antennas and measuring them. Results of these studies are presented in this paper together with results of the measurements of the full size antenna at Andover, Maine.
An E-plane cut (Fig. 6) was obtained for both the Camegrainian (solid curve) and its equivalent paraboloid (broken curves). The gain discrepancy remains small after the beam has been scanned by about four beamwidths. When four primary radiators with proper phasing and with Ax = 2X for each feed are clustered to form an amplitude comparison monopulse system, the resultant difference patterns are shown in Fig. 7, which shows tha.t the gain discrepancy is negligible. IV. CONCLUSIOKA useful expression has been derived t.o obt,ain the vector diffraction field of a reflector antenna with an offset feed. Both the sum and difference patterns of a well designed Cassegrainian syst.em can be predicted with a fair degree of accuracy using t,he equivalent parabola technique. The error in gain resulting from the use of the simplified technique remains small when the beam is squinted by about four beamwidth.
An antenna suitable for ground stations of satellite communications systems is described. The antenna has very good low‐noise properties, high aperture efficiency, and excellent broadband characteristics. It can be operated without a radome and allows the location of all communications and tracking equipment in a stationary room on the ground. Called the “triply‐folded horn‐reflector antenna,” it is derived from the well‐known conical horn‐reflector antenna by folding the horn three times to bring its apex into a stationary position on the ground. Plane reflectors are used in the folding process and the propagation in the antenna is based on the principles of geometrical optics. The paper describes electrical tests on an antenna model at frequencies of 60 and 11 gc and presents results of hydrodynamic tests which were performed to study the behavior of the antenna in high wind.
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