A Modified Analog Predistorter Using Tunable Power Divider for Wideband 5G Transmitters

Advanced communication system such as 5G demands high data rate and wideband signals. These signals have a high peak-to-average-power ratio (PAPR), which drives the power amplifier (PA) to early saturation. This brief proposes an analog predistortion method to linearize the power amplifier (PA) for wideband transmission systems like 5G. It utilizes a rat-race-coupler-based intermodulation generator to generate intermodulation terms, and it uses a Tunable-power divider (T-PD) based on varactor diode-controlled crossover structures to control the characteristics of the predistotered signal. This removes the dependencies on the bulky vector modulator which is frequently used in the conventional APD design. This also reduces the overall footprint. In order to validate the concept, the proposed APD with PA is tested with 64-QAM OFDM test signals of bandwidth 20 MHz and 100 MHz. It achieves a maximum improvement in the adjacent channel power ratio (ACPR) and normalized mean square error (NMSE) of 23.67 dB and 18.21 dB, respectively, over that of PA. Though the components are designed at a center frequency of 3.5 GHz, the proposed method is tested in a frequency range of 3 to 3.8 GHz and provides a significant improvement in ACPR and NMSE across the entire frequency range.