# A Review of Ku-Band GaN HEMT Power Amplifiers Development
###### Abstract  
This review article investigates the current status and advances in Ku-band gallium nitride (GaN) high-electron mobility transistor (HEMT) high-power amplifiers (HPAs), which are critical for satellite communications, unmanned aerial vehicle (UAV) systems, and military radar applications. The demand for high-frequency, high-power amplifiers is growing, driven by the global expansion of high-speed data communication and enhanced national security requirements. First, we compare the main GaN HEMT process technologies employed in Ku-band HPA development, categorizing the HPAs into monolithic microwave integrated circuits (MMICs) and internally matched power amplifier modules (IM-PAMs) and examining their respective characteristics. Then, by reviewing the literature, we explore design topologies, major issues like oscillation prevention and bias circuits, and heat sink technologies for thermal management. Our findings indicate that silicon carbide (SiC) substrates with gate lengths of 0.25 \(\upmu\)m and 0.15 \(\upmu\)m are predominantly used, with ongoing developments enabling MMICs and IM-PAMs to achieve up to 100 W output power and 30% power-added efficiency. Notably, the performance of MMIC power amplifiers is advancing more rapidly than that of IM-PAMs, highlighting MMICs as a promising direction for achieving higher efficiency and integration in future Ku-band applications. This paper can provide insights into the overall key technologies for Ku-band GaN HPA design and future development directions. Ku-band; GaN HEMT; high-power amplifier; satellite communications; MMIC; IM-PAM 2024153  
The frequency bands used for satellite communications are primarily divided into C-band, X-band, Ku-band, and Ka-band. Among these, Ku-band and Ka-band offer advantages such as supporting large data transmission, providing high-resolution services with wide bandwidth, and enabling antenna miniaturization due to their shorter wavelengths [4]. However, due to the high operating frequency, the performance of transceiver modules used in towers and earth stations has been limited, making development challenging. Recent advances in complementary metal-oxide-semiconductor (CMOS) and gallium nitride (GaN) high-electron mobility transistor (HEMT) semiconductor process technology have, however, enabled commercialization. Ku-band is now used not only for satellite communication but also in transmitter and receiver modules (TRMs) for unmanned aerial vehicle (UAV) communication, which is increasingly being utilized alongside satellites due to its advantages in miniaturization and bandwidth [7]. Table 1 compares the electrical properties of major semiconductor materials [8], while Figure 2 illustrates the breakdown voltage characteristics as a function of cutoff frequency for semiconductor devices [9; 10]. As shown in Table 1 and Figure 2, GaN HEMT semiconductors have been widely studied and commercialized as high-frequency power semiconductors due to their high breakdown voltage and excellent electron mobility stemming from their wide energy band gap. High-power amplifiers (HPAs) present significant challenges in achieving performance in Ku-band satellite and UAV TRMs. To attain high output power, traveling wave tube amplifiers (TWTAs), which utilize vacuum tube technology, have traditionally been employed; however, they are heavy and unstable due to their high-voltage operation. Now, advances in GaN HEMT semiconductor process technology are enabling the replacement of conventional TWTAs with solid-state power amplifiers (SSPAs) [11; 12]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Property** & **Si** & **GaAs** & **SiC** & **GaN** \\ \hline Energy Bandgap (eV) & 1.11 & 1.43 & 3.2 & 3.4 \\ Critical Electric Field (MV/ cm) & 0.3 & 0.5 & 3.0 & 3.5 \\ Charge Density (\(\times 10^{13}\)/cm\({}^{2}\)) & 0.3 & 0.3 & 0.4 & 1 \\ Mobility (cm\({}^{2}\)/V/s) & 1350 & 8000 & 900 & 1500 \\ Saturation Velocity (\(\times 10^{7}\) cm/V) & 1 & 1.4 & 2 & 2.7 \\ \hline \hline \end{tabular}
\end{table}