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BBC R&D White Paper WHP066

Specifying UHF Active Antennas and Calculating System Performance
John Salter

Keywords
noise-figure, noise-temperature, G/T

Abstract
An active antenna consists of a passive antenna followed by and combined with a low noise pre-amplifier. Because the combination cannot be separated for measurements it is best considered, with relevant parameters, as a single entity. This White Paper gives a brief review of receiver noise theory when the receiver is fed from a passive or an active UHF antenna. It shows how an active antenna could be specified in a simple way in terms of total gain and noise temperature. This enables system noise parameters for an active antenna to be readily calculated and compared to the familiar passive antenna.