Over-the-Air Suppression of Third-Order Intermodulation in a Two-Beam Steered Amplifier-Antenna Array

Abstract

The effect of load-pull on 3rd order intermodulation (IM3) radiation characteristics of a transmitting active phased array is studied and a general model for predicting the spatial distribution of fundamental tones and intermodulation products is introduced. The used data is obtained from a load pull measured amplifier prototype and a simulated linear antenna array, which are used in co-simulation of the system behavior. The system is optimized for maximum main tone beam powers with a two-tone excitation while satisfying a signal-to-IM3 ratio (SI3R) of 40 dB. In this paper, we demonstrate the case, where two separate beams are scanned independently from each other. The used load-pull system model achieves on average an improvement of 10.4 dB for SI3R, when compared to traditional small-signal modelling, while decreasing the main beam power densities by only 0.3 dB when compared to traditional small-signal modelling. Optimizing for SI3R degrades beam pattern by increasing beamwidths and decreasing sidelobe levels (SLL).

Keywords

• Active phased arrays
• amplifier
• beam-steering
• intermodulation
• load pull
• third-order intermodulation product (IM3)