Prediction of Nonlinear Distortion in Wideband Active Antenna Arrays

Abstract

In this paper we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multiantenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of taking into account the joint effects of PA nonlinearity, antenna crosstalk and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12 GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics, as for example the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems. Index Terms-Active antenna array, antenna crosstalk, mismatch, MIMO transmitter, power amplifier modeling I. INTRODUCTION Wireless communication systems face a steadily growing demand for higher data rates. However, the radio spectrum is a limited resource. Multiple-input multiple-output (MIMO) systems can be utilized to increase spectral efficiency [1]. For this reason, modern wireless telecommunication standards, such as LTE and Wi-Fi, include the use of multiple antennas. Largescale antenna systems, which comprise hundreds of antennas, have become a hot topic in the research community [2]. The use of several transmit paths in a transmitter (TX) increases system complexity and cost [3]. Therefore, integrated solutions, as have been used in, e.g., radar applications for many years, are preferred. Such integrated designs avoid costly components like bulky isolators between power amplifiers This research has been carried out in GigaHertz Centre in a joint project financed by the

Digital Predistortion Concepts for Linearization of mmW Phased Array Transmitters

“…The variations in antenna matching [20] has a direct impact on the PA behavior and may depend even on the phase shifter control [10]. Furthermore, in [21] it is discussed that also strong enough antenna coupling could cause differences in the nonlinearities of individual PAs. Finally, even if all the previously mentioned effects were ignored, the branch-specific gain control, used to shape the beam (beamforming), to create nulls or reduce the sidelobes [8], makes each nonlinear path different from each other.…”

Analyzing the Effects of PA Variations on the Performance of Phased Array Digital Predistortion

“…[8] However, if the input amplitudes or the nonlinear characteristics of the individual PAs are varied, the beam pattern of the nonlinearity differs from the linear beam. Furthermore, in [9] it is discussed that also strong enough antenna coupling would cause differences on the nonlinearities of individual PAs. Hence, the nonlinearity of an array may depend on the direction of observation.…”

Digital Predistortion for Multi-Antenna Transmitters Affected by Antenna Crosstalk

“…However, such systems are vulnerable to antenna crosstalk due to mutual coupling and antenna mismatches [3]. As a consequence, integrated multi-antenna transmitters typically suffer from nonlinear distortion due to the mixing of the antenna crosstalk and mismatch with the PA output, in addition to the nonlinear distortion caused by the behavior of the PAs [4], [5]. To avoid This research has been carried out in GigaHertz Centre in a joint project financed by the Swedish Governmental Agency for Innovation Systems (VIN-NOVA), Chalmers University of Technology, Ericsson, Infineon Technologies Austria, Ampleon, National Instruments, Gotmic, and Saab.…”

“…[6], [7], which are designed for systems with only one transmit path. Single-input DPD can compensate for PA nonlinearity, but not for the effects caused by antenna crosstalk, and is therefore not suitable for multi-antenna systems [4], [5].…”