Receiver G/T Analysis of Phased-Array-Fed Lens Systems

Phased-Array-Fed Lenses (PAFLs) are a promising low-power alternative to Phased Array Antennas (PAAs) through the use of a lens aperture and activating sub-arrays of its full feed array. While PAFL beam pattern synthesis is well understood, the antenna gain-to-noise temperature ratio (G/T) of receiving PAFL systems has not been well characterized. This work analyzes PAFL G/T, focusing on a unique challenge: passive power combiners introduce severe losses when driven by sparse active elements. We propose adding amplifiers within the beamforming network to counteract these losses. The analytical model is validated through measurements of a 4-element PAA feeding a gradient index (GRIN) lens at 35 GHz. Using the CW-ambient method, results match the model within 1 dB. Findings demonstrate that a properly designed PAFL system can match the G/T of an equivalent PAA while retaining its intrinsic low-power advantage.