Abstract
The second-harmonic input impedance plays a critical role on the performance of GaN power amplifiers. In a recent paper, a drain efficiency enhancement for a continuous-mode power amplifiers was reported to be achieved using active broadband second-harmonic injection at the PA input. In this paper, the strategy for selecting the second-harmonic input impedance and the necessity for using active injection in such broadband PAs are discussed in detail. Additionally, the methodology for designing an embedded broadband diplexer in the input matching network is reported. Finally, the importance of the phase of the second-harmonic signal injected is demonstrated for both CW and modulated signals using both simulation and measurement, respectively. The effectiveness of the CW and modulated active second-harmonic injection methodology presented here are validated by previously reported measurements that demonstrated an average drain efficiency improvement of 9.4% from 1.3 to 2.4 GHz for CW signals and of 9.7% at 2 GHz for a frequency-modulated 30 MHz chirp radar signal.
Highlights
There is growing interest in realizing highly efficient power amplifiers (PA) for radar applications using Gallium Nitride (GaN) technology
Broadband efficiency enhancements using input second-harmonic injection is experimentally verified in this article for the first time for both CW and modulated signals when using an embedded broadband diplexer design
The second-harmonic signal is injected through the embedded broadband bandpass filter at the gate of the packaged transistor to further enhance the efficiency via the tuning of the intrinsic output loadlines of the transistor
Summary
There is growing interest in realizing highly efficient power amplifiers (PA) for radar applications using GaN technology. Various studies have drawn attention to the correlation between the input second-harmonic source impedance ZS (2ω ) and the drain efficiency especially for GaNbased PAs [8,9,10,11,12,13]. An assisted input second-harmonic injection allows the designer to place the ZS (2ω ) close to the maximum-efficiency region while providing the capability of compensating for a possible simulation–measurement discrepancy. The input secondharmonic injection was discussed in a few papers that directly injected the fundamental and second-harmonic signal at the transistor’s gate using a lossy external combiner without a physical IMN or filter [14,15,16].
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