# Highly Efficient GaN Doherty Power Amplifier for N78 Sub-6 GHz Band 5G Applications
## 1 Introduction  
The demand for high-performance RF power amplifiers (PAs) has surged with the advent of 5G wireless communication networks. These PAs play a pivotal role in ensuring seamless signal transmission, making them critical components in bridging the gap between transmitters and receivers. Many applications depend mainly on PAs as detection systems [1], hyperthermia therapy system [2, 3], and wireless communications networks [4]. Some of the most important wireless communication networks are the 5G networks. As 5G networks continue to expand, particularly with the deployment of small cell networks, the management of power consumption and heat dissipation in wireless base stations poses significant challenges for system designers. The exponential growth in data rates and the increasing complexity of modulation schemes, such as 4096 Quadrature Amplitude Modulation, mandate PAs that are not only highly efficient but also capable of handling high peak-to-average power ratios (PAPR). The integration of multiple-input multiple-output(MIMO) transmissions further complicates transmitter design, underscoring the need for wideband, high-efficiency PAs with compact footprints [5]. Gallium nitride (GaN) PAs have emerged as promising candidates, particularly for the 5G sub-6 GHz band. GaN offers advantages such as high power density, efficiency, and wideband performance. Moreover, GaN technology exhibits low thermal resistance and can operate at high frequencies, aligning well with the demands of 5G networks. PAs operating in the FR1 range must efficiently handle complex modulations with high PAPR, making high-efficiency PAs a necessity [6; 7]. Various methods and architectures have been proposed to enhance PA efficiency, especially at output power back-off (OPBO) levels. These include the Doherty power amplifier (DPA) [7; 8; 9], Chireix-outphasing PAs [10; 11; 12], Envelope Elimination and Restoration (EER) [13; 14], Envelope Tracking (ET) methods [15; 16], and Power Combining methods [17; 18]. Among these, DPA stands out due to its simplicity, reliability, and excellent linearity. Recent advancements have expanded its bandwidth through innovative strategies. While improving DPA bandwidth is critical, it often leads to increased circuit complexity. Strategies like output compensation stages and subsequent matching networks [7; 19], an unusual inverted impedance network [20], and digital approaches [10; 12] have been employed. This paper addresses the challenge of maintaining a DPA's basic structure while achieving broad bandwidth and exceptional efficiency. DPAs are designed to split and combine power at the amplifier's input and output, respectively. The power divider circuit, which plays a crucial role in optimizing linearity, offers an optimal power split ratio based on input power. Various power divider methods, such as quadrature hybrid couplers [21; 22], equal-split Wilkinson's [23; 24], and the dual-input Doherty technique that utilizes digital input processing for optimal splitting [25; 26], have been explored. In our study, we employed the unequal-split Wilkinson's method and included a harmonic suppression circuit at the DPA network's output to ensure both linearity and maximum efficiency. In this paper, we present the design and simulation of a PA based on the CG2H40010F GaN HEMT from Wolfspeed, operating in the 3 GHz to 4 GHz frequency range, covering the 5G N78 band (3.3 GHz-3.8 GHz). The Advanced Design System (ADS) software version 2022, provided by Keysight Technologies, was utilized for RF circuit design. This research contributes significantly to the field of RF power amplifiers for 5G applications. The main contributions include the following:  
* Proposed a design for a high-efficiency GaN Doherty power amplifier tailored to the N78 sub-6 GHz band, the most widely used band in active 5G NR networks. * Significantly improved PAE by 27% through the incorporation of a 2.5:1 unequal Wilkinson power divider at the amplifier's input, in contrast to using an equal Wilkinson divider.