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This paper presents the design of a RF Pulse Width Modulator (RF-PWM) for switched-mode power amplification of varying envelope signals. The general idea is to modulate the varying envelope signal using squarewave signals with varying width and subsequently drive a class D-type power amplifier. The linearity in the modulator is ensured by a novel combination of low frequency feedback combined with predistortion.Measurements on a frequency wise down-scaled prototype show that the RF-PWM modulator modulates a UMTS signal with more than 17 dB margin to the modulation mask and EVM below 0.5% RMS. This leads to the conclusion that sufficient linearity and modulation accuracy can be obtained using RF Pulse Width Modulation.

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By increasing the number of antennas and power amplifiers connected to each in 5G system, the linearization methods like digital pre-distortion (DPD) of each power amplifier is inefficient due to antenna imperfections such as crosstalk. As a result of limited area the distance between antennas in array can vary which leads to unwanted coupling between antennas. A solution to this problem could be treating the amplifiers and antennas as one system and linearizing the main beam signal at the receiver rather than on each single power amplifier. In the work described in this paper, the whole system including amplifiers, antennas and the receiver is treated as a 2-ports system and the impacts of the above mentioned constraints are investigated.

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