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There has been intensive research in memoryless nonlinear behavioral modeling of power amplifiers (PAs). But in broadband communication systems, memory effects of PAs can no longer be ignored and traditional memoryless model cannot accurately characterize the input-output relationship of PAs. In order to treat memory effects and reduce the complexity of general Volterra model, a new behavioral PA model based on modified Volterra series is proposed. Since the characteristics of power amplifiers change during transmission time, a recursive least squares algorithm with size-fixed observation matrices is developed to update the parameters of the PA model. This identification algorithm, which uses only the latest sample data to identify the parameters, can decrease computational complexity and data storage space needed for identification. Simulations are carried out to validate the performances of the proposed PA model and identification algorithm.

In this paper, a new linearization algorithm of power amplifier (PA), based on Kalman filtering theory is proposed for obtaining fast convergence of the adaptive digital predistortion. The proposed method uses the real-time digital processing of baseband signals to compensate the nonlinearities and memory effects in radio-frequency power amplifier. To reduce the complexity of computing in classical Kalman filtering, a sliding time-window has been inserted which combines offline measurement and online parameter estimation with high sampling time to track the changes in the PA characteristics. The performance of the proposed linearization scheme is evaluated through simulation and experiments. Using digital signal processing, experimental results with commercial power amplifier are presented for multicarrier signals to demonstrate the effectiveness of this new approach.

This paper reports a refined multi-tone waveform measurement system for the robust characterization and optimization of nonlinear microwave devices when driven by broadband multi-tone stimuli. This enhanced system has the ability to present specific, constant broadband impedances, not only at baseband (IF) frequencies, but also at RF frequencies, particularly, around the carrier and significant harmonics. This functionality is key in studying the effects of out-of-band impedance termination on both short and long-term electrical memory effects. Achieving such comprehensive impedance control across wide modulation bandwidths is also critical in allowing the "emulation" of emerging power amplifier modes and architectures, and the subsequent waveform characterization of devices operating in these complex and often dynamic impedance environments. Initially, the baseband load-pull capabilities of the enhanced measurement system are experimentally demonstrated through the measurement of adjacent channel power (ACP) behavior of a class AB biased 10 W GaN HEMT, in response to a varying baseband load. Complete baseband and RF impedance control is then demonstrated through the emulation and analysis of a modulated Class-J impedance environment, which interestingly highlights the presence of separate optimum baseband impedance conditions necessary for the suppression of individual IM products.

In this paper, an innovative approach to achieve broadband linear power amplifier (PA) with a continuous broadband is presented. The proposed method mainly depends on the theory of control of intermodulation products and harmonics. This method results in a continuous sweet spots over a wide bandwidth. Based on the continuous sweet spots, a suboptimal solution is derived for improving the efficiency and linearity of broadband PAs. To verify the effectiveness of this method, one broadband PA operating over 4.5–5.5GHz is developed and measured, it indicates that the peak output power of the PA is 35–57dBm for a small signal input with a gain of 12dB, and the peak drain efficiency (DE) of the PA is larger than 57% over the whole working band. However, when the PA is stimulated by a 5MHz two-tone signal input, we observe that the DE keeps above 38% under the condition of the measured third-order intermodulation distortion (IMD3) is not larger than $-30$dBc.

Recent decades have seen significant progresses in the field of power amplifiers (PAs). In order to present the evolution of the field, this paper shows the development trends of the PA research based on the statistical analysis from 1970 to 2017. The brief history of radio frequency (RF)/microwave PAs and a comprehensive review on the evolution of RF/microwave PAs are presented. The state-of-the-art PAs thus far based on the statistical analysis in terms of the figure of merit (FoM) of RF/microwave PAs have been discussed in this paper. A quantitative relationship of trade-off of PA performance metrics is proposed, and the potential room for improvement of the performance of the PAs is also revealed.