A Novel Second Harmonic Generator Scheme with Application in Linearization of Power Amplifiers

This paper presents the design and fabrication of two second harmonic (SH) signal generators based on GaAs (HG1) and GaN (HG2) technologies, which simultaneously perform the same function as a variable amplifier, phase shifter, and attenuator. With the capability to adjust its impedance matching capacitors, this integrated network produces a variable amplitude and phase shift at the second harmonic frequency. This design is a good choice for performance in active feedback linearization. It has been shown that by injecting the output signal of the power amplifier to the input of the SH signal generator and applying its output to the input of the power amplifier, a significant improvement in third-order intermodulation (IMD3) and adjacent channel power ratio (ACPR) can be achieved. To investigate the linearization performance of both categories, 2-tone and modulated signal tests are performed on a 10 W GaN power amplifier at 1.5 GHz with the proposed circuit. The measured data show a 24 dB decrease in IMD3 and a 13 dB decrease in ACPR for a 4-MSPS 64-QAM modulated signal compared to the power amplifier at 3 dB back-off.