  Citation: Yang, F.; Yu, H.;Li, J.; Guo, C.; Yan, S.; Chen, X.; Zhang, A.; Jin, Z. A Class-F Based Power Ampliﬁer with Optimized Efﬁciency in Triple-Band. Electronics 2022, 11, 310. https://doi.org/10.3390/ electronics11030310 Academic Editor: Hirokazu Kobayashi Received: 30 November 2021 Accepted: 17 January 2022 Published: 19 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). electronics Article A Class-F Based Power Ampliﬁer with Optimized Efﬁciency in Triple-Band Fei Yang 1 , Hongxi Yu 1 , Jun Li 1 , Chao Guo 1 , Sen Yan 2 , Xiaoming Chen 2 , Anxue Zhang 2, * and Zhonghe Jin 3 1 China Academy of Space Technology (Xi’an), Xi’an 710100, China; yfxjtu@163.com (F.Y.); yuhongxi123@aliyun.com (H.Y.); liurz1388@163.com (J.L.); 3140103482@zju.edu.cn (C.G.) 2 School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China; sen.yan@xjtu.edu.cn (S.Y.); Xiaoming.chen@mail.xjtu.edu.cn (X.C.) 3 School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310058, China; jinzh@zju.edu.cn * Correspondence: anxuezhang@mail.xjtu.edu.cn Abstract: A Class-F mode-based power ampliﬁer (PA) with optimized efﬁciency in triple-band was designed using a simple and systematic approach. By considering the second and third harmonic terminations of the PA, the relationship between the output impedance design space and the drain efﬁciency (DE) is extracted by large-signal model simulation. Then, a low-pass matching topology is utilized for the triple-band efﬁciency optimization. The method is justiﬁed by both simulation and measurement of a triple-band PA to integrate three functions into one hardware, i.e., 1518–1525 MHz for mobile communication, 2.1 GHz for telemetry and control, and 2.492 GHz for navigation signal transport. The proposed PA achieves a measured result of high DE (63% at 1.52 GHz, 71% at 2.1 GHz, 59% at 2.492 GHz) in the three bands with an output power of at least 40 dBm. Keywords: triple-band; class-F; power ampliﬁer 1. Introduction Today, to address the increasing demands of modern wireless communication ter- minals, it is necessary to cover different standards with a single piece of hardware, and thus, a multi-band transmitter is a key technical challenge [1–5]. To achieve dual-band or multi-band operation with one highly efﬁcient power ampliﬁer (PA) circuit, the design does not only need the correct fundamental loads transformation, but also the proper higher harmonic impedance terminations [6,7]. A common approach to address this problem is to design a broadband PA that cov- ers all the operation bands [7–11]. The fundamental impedance matching with 50-Ohm load is the ﬁrst step to overcome. Additionally, the second and the third harmonic load terminations also need to be considered to improve the efﬁciency by various approaches. However, most of the designs failed to solve the challenge and to realize the optimization in operating multi-bands, e.g., the methods proposed in [11–14] are focusing on the broadband performance, rather than the bands of interest in our application [15–20]. The idealized Class-F mode is termed as a waveform of a squared-up voltage wave, which contains only fundamental components, odd higher harmonic components and a half-wave rectiﬁed sinusoidal current waveform at its intrinsic current source (I gen )[1,2]. With an inﬁnite number of harmonics, an ideal drain efﬁciency (DE) of 100% can be obtained and the voltage waveform can be a perfect square waveform. When the controlled harmonic impedances up to the third order, the DE can achieve π/4 × 2/ √ 3 (90.7%), and the fundamental output power will increase 2/ √ 3 (0.6 dB) in the maximum efﬁciency condition [1,2]. Figure 1 shows the waveform and the load-line of the idealized and the realistic 10-watts transistor used in this paper, namely Cree 10-W gallium nitride high electron mobility transistor (GaN HEMT), CGH40010F. As described in Figure 1, the voltage Electronics 2022, 11, 310. https://doi.org/10.3390/electronics11030310 https://www.mdpi.com/journal/electronics