A Compact Load-Modulation Amplifier for Improved Efficiency Next Generation Mobile

Current and future mobile communications systems are aimed to increase the achieved efficiency at the backoff and to reduce the required size for the amplifier. A load modulation amplifier targeting 3.4-3.8 GHz is designed, simulated and fabricated to achieved the maximum achievable back-off efficiency from the peak power. The amplifier uses a special technique to implement the load modulation amplifier without using a quarter wave-length transmission line. The measured results showed a 48 dBm peak power with efficiencies of >75 %, >60 %, >55 % and >51 % at 0 dB, 6 dB, 8 dB and 10 dB back-off power respectively for the whole designed bandwidth. The amplifier was tested an LTE modulated signal where the Adjacent Channel Power Ratio (ACPR) was 30 dB and it was improved by utilising a digital predistortion to be 48 dB.