G/T AND NOISE-FIGURE OF ACTIVE ARRAY ANTENNAS

A figure of merit, G/T, for a multichannel active array antenna was derived, and the effects of the beam-forming network on the overall noise figure of the system was studied. Also examined in the paper are the dependence of the noise figure on various losses, and the difference between a resistive and nonresistive taper in the combining network. When the amplifier gain is sufficiently large, the losses following the LNA can usually be ignored. For a photonic array with lossy time shift elements, however, the downstream losses become significant. Also, if resistive tapering is employed, not only the array pin but also the noise figure will be degraded by the collective effect of the feed network.