Search Results (2)

This paper presents the theory, design, and application of a dual-branch series-diode analog pre-distortion (APD) linearizer to improve the linearity and efficiency of a K-band high-power amplifier (HPA). A first-of-its-kind, frequency-dependent large-signal APD model is presented. This model is used to evaluate different phase relationships between the linear and nonlinear branches, suggesting independent gain and phase expansion characteristics with this topology. This model is used to assess the impact of diode resistance, capacitance, and ideality factors on the APD characteristics. This feature is showcased with two similar GaAs diodes to find the best fit for the considered HPA. The selected diode is characterized and modeled between 1 and 26.5 GHz. A comprehensive APD design and simulation workflow is reported. Before fabrication, the simulated APD is evaluated with the measured HPA to verify linearity improvements. The APD prototype achieves a large-signal bandwidth of 6 GHz with 3 dB gain expansion and 8° phase rotation. This linearizer is demonstrated with a 17–21 GHz GaN HPA with 41 dBm output power and 35% efficiency. Using a wideband 750 MHz signal, this APD improves the noise–power ratio (NPR) by 6.5–8.2 dB over the whole HPA bandwidth. Next, the HPA output power is swept to compare APD vs. power backoff for the same NPR. APD improves the HPA output power by 1–2 W and efficiency by approximately 5–9% at 19 GHz. This efficiency improvement decreases by only 1–2% when including the APD post-amplifier consumption, thus suggesting overall efficiency and output power improvements with APD at K-band frequencies. Full article

In this article, a Ka-band broadband analog predistortion (APD) microwave monolithic integrated circuit (MMIC) with independent tunability based on a 0.15 μm GaAs pHEMT process is proposed, which can be cascaded in front of traveling wave tube amplifiers (TWTAs) to improve their linearity. The influence of different diode sizes on the parameters of Schottky diodes is analyzed and used to design the gain and phase nonlinear branches. The broadband APD MMIC is realized based on a dual-branch vector synthesis design and nonlinear frequency adjust module (NFAM). The independent tunability and broadband characteristics of the APD MMIC are verified by simulated and measured results with an error of less than 5%. Furthermore, a Ka-band 60 W TWTA is linearized by the APD MMIC, and the gain and phase compressions are reduced from 8 dB and 50° to within 3 dB and 12°, respectively. The third-order intermodulation (C/IM3) is greater than 28 dBc and noise power ratio (NPR) is greater than 15.7 dBc at 3 dB output power backoff (OPBO) over the operating band of 25.1~27.5 GHz, indicating that the APD MMIC can improve the nonlinearity of TWTA effectively under broadband signals. Full article