Modelling of Intermodulation Products from a Multiple Beams Transmitter Under Antennas Crosstalk

With the advent of new generations of telecommunications, the deployment of active direct radiating arrays (DRA) delivering multiple beams across multiple frequencies holds great promise, particularly for Low Earth Orbit (LEO) applications. In these advanced technologies, assessing active circuit nonlinearities and the effects of coupling and mismatch within antenna arrays is increasingly critical. As the industry moves towards eliminating bulky and power-consuming isolators from active DRAs, the mutual coupling between antennas will inevitably alter the load impedance perceived by the power amplifiers (PAs). Given that PA performance is closely tied to the load impedance, we can expect fluctuations in the DRA's performance. This effect is usually referred as Load-Pull Effect. However, evaluating these techniques experimentally poses significant challenges in terms of time, resources, and expenses. Furthermore, existing modelling tools in commercial software may encounter either prolonged computation times or convergence issues as the number of beams and radiating elements is increased. This article presents a hardware-oriented modeling approach designed to predict the intermodulation products (IMDs) generated by systems affected by active circuit nonlinearities and antenna crosstalk. The proposed tool employs a memoryless mixed Time-Frequency domain method to compute the spectral regrowth from each PA experiencing the load-pull effect. This modeling approximation is well-suited for narrowband signals, providing a balance between computation time and accuracy. The model is compared with commercial software solutions for DRA operating in the Sub-X band. The comparison involves an assessment of the spectral regrowth signal and the evaluation of the Equivalent Isotropically Radiated Power (EIRP) far-field radiation pattern to demonstrate the degradation in DRA performance. Results indicate a significant reduction in computation time while maintaining a high level of accuracy. Given that some LEO applications can be classified as narrowband, this tool is highly suitable for evaluating system performance. The paper will also demonstrate its application to a direct-to-cell S-band scenario.