Effect of signal to noise ratio degradation due to RF level variation on active antenna performance

Active phased array antenna consists of a number of radiating elements excited by active RF modules with transmit and receive chain. The performance of the array depends upon stability and accuracy of amplitude and phase excitation at input of elements during transmit mode or at input of receiver during receive mode of operation. To achieve desired performance of an active array, calibration (correction of amplitude and phase errors) of all RF paths consisting of active modules need to be done. Accuracy of calibration depends upon Signal to Noise Ratio (SNR) at individual RF path. This paper describes the effect of SNR degradation at active path on the array performance, due to variation of RF level of injected reference signal used for calibration of the array. The study has been done on variation in array characteristic such as beam width, side lobe levels etc. due to poor SNR level in active RF path. The measured results of calibration network of a realized active array with about 2000 active elements has been used to derive the SNR of the network and simulation results have been generated. The simulated and measured pattern has been compared and presented.