Degradation in the efficiency of medium-size parabolic antennas with propagation conditions

The results of a simple, short-term experiment suggest that significant errors may arise in the overall design and costing of a communication system where parabolic antennas are employed at the receiver terminal. Under high signal conditions the relative gains of two parabolic antennas of different diameters are in close agreement with the theoretically predicted value. Under low signal conditions, when a larger diameter antenna might be preferred in practice, there appears to be a considerable reduction in the proportion of power collected by a large antenna in relation to the proportion collected by an antenna of significantly smaller diameter.