Percorrer por autor "Carvalho, Nuno Borges"
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- The impact of long-term memory effects on diode power probesPublication . Gomes, Hugo; Testera, Alejandro R.; Carvalho, Nuno Borges; Barciela, Mónica F.; Remley, Kate A.This paper presents an analysis of long term-memory effects on power measurements with diode power probes. We show that a power probe calibrated with a single-tone sinusoidal excitation can provide erroneous values when used with modulated signals. This fact is ascribed to the low-frequency response imposed by the power probe baseband circuit. This hypothesis is first theoretically demonstrated by use of a Volterra series, and then validated by simulations and measurements using a diode power probe.
- A Survey on Over-The-Air Linearization Methods for MIMO SystemsPublication . Jordão, Marina; Caldeirinha, Rafael; Oliveira, Arnaldo S. R.; Carvalho, Nuno BorgesTransmitter antenna arrays are typically coupled to several RF chains, which imposes stringent requirements on the linearization of each power amplifier (PA) present in the system. For this and other reasons discussed in this work, Over-the-air (OTA) linearization methods are considered to linearize transmitter antenna arrays in 5G scenarios. However, several factors need to be considered when applying OTA linearization methods. In this paper, an extended critical review of validated OTA linearization methods is presented. The main goal is to point out and discuss the most prominent methods, in order to determine which one is the most suitable for a specific application. In particular, analysis for each method is performed and, subsequently, their benefits and the disadvantages are systematically discussed. This is sought to fill-in a gap in the scientific literarure and, thus, to help radio-frequency engineers in the implementation of OTA digital pre-distortion (DPD) techniques for multiple input multiple output (MIMO) systems.