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
Aluminium gallium nitride (AlGaN)/GaN high-electron mobility transistor performance is to a large extent affected by the buffer design, which, in this paper, is varied using different levels of carbon incorporation. Three epitaxial structures have been fabricated: 1) two with uniform carbon doping profile but different carbon concentration and 2) one with a stepped doping profile. The epitaxial structures have been grown on 4H-SiC using hot-wall metal-organic chemical vapor deposition with residual carbon doping. The leakage currents in OFF-state at 10 V drain voltage were in the same order of magnitude (10 −4 A/mm) for the high-doped and stepped-doped buffer. The high-doped material had a current collapse (CC) of 78.8% compared with 16.1% for the stepped-doped material under dynamic I-V conditions. The low-doped material had low CC (5.2%) but poor buffer isolation. Trap characterization revealed that the high-doped material had two trap levels at 0.15 and 0.59 eV, and the low-doped material had one trap level at 0.59 eV.Index Terms-Current collapse (CC), dispersion, gallium nitride (GaN), high-electron mobility transistor (HEMT), trap levels.
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