###### Abstract  
This article presents a 26-30 GHz gallium nitride (GaN) high electron mobility transistor (HEMT) low-noise amplifier (LNA) for fifth-generation base station applications. In the proposed design, a series inductor-based stability enhancement technique was utilized to improve the reverse isolation and stability performance of the amplifier and to mitigate the effect of the parasitic capacitance of the GaN HEMT device. To validate the concept of the design, a three-stage GaN HEMT LNA was designed and fabricated in a 0.15-um GaN on silicon carbide technology. The demonstrated design achieved a gain of 20.2 dB, a noise figure of 2.4-2.5 dB, an output 1-dB compression point of 17.2 dBm, and an output third-order intercept point of 32.2 dBm. The design also attained stability (\(\mu\) criterion) up to 7.7 at the operating frequency. The implemented design consumed power of 320 mW with a nominal supply of 10 V.  
fifth generation (5G); gallium nitride (GaN); high electron mobility transistor (HEMT); low-noise amplifier (LNA); millimeter wave; silicon carbide (SiC); stability Article  
because GaAs devices generally provide good electron mobility and noise characteristics [12; 13; 14; 15]. However, as depicted in Figure 1a, the limited high-power robustness of GaAs devices necessitates additional protection circuits such as an isolator and/or a limiter at the input of the receiver front end, which substantially exacerbates the design complexity and noise performance of the FEM design. On the other hand, a GaN HEMT-based LNA with a single-pole double-throw (SPDT) switch (Figure 1b) no longer needs those protection circuits owing to their own inherent high-power endurance [16]. Therefore, through the elimination of these extra protection circuits, reduced size and improved noise performance can be realized in the FEM design with the additional possibility of a low-cost single-chip solution by integrating the LNA, PA, and SPDT within a single die. Moreover, as the scaling of GaN technology shrinks and corresponding breakdown voltage increases, the noise characteristic of GaN devices becomes comparable to that of their GaAs and indium phosphide (InP) counterparts. Because of these benefits, various GaN HEMT-based LNAs have been reported in recent studies [17; 18; 19; 20; 21; 22; 23; 24]. However, in the design of GaN HEMT-based amplifiers, stability performance is also a major concern, which is directly related to the reverse isolation characteristic (S12) of the amplifier. Specifically, in the mmWave frequency range, high frequency path losses and parasitic capacitance readily affect isolation characteristics. This eventually causes an extra design trade-off between stability and maximum available gain (MAG) performance.  
In this study, we demonstrate a 26-30 GHz GaN HEMT LNA monolithic microwave integrated circuit (MMIC) using a 0.15-\(\upmu\)m GaN-on-silicon carbide (SiC) process. By adopting series inductors at the drains of the device, the reverse isolation and stability performance of the amplifier are eventually improved at the operating frequency with minimum impact on the overall MAG and noise figure (NF) performance. The implemented design is targeted for application in the phased-array antenna structure for 5G base stations, which support the n257 (26.5-29.5 GHz) and n261 (27.5-28.35 GHz) bands of the 5G NR frequency range 2 (FR2) [1]. The remainder of this paper is organized as follows: In Section 2, several performance parameters of the utilized 0.15-\(\upmu\)m GaN-on-SiC process are emphasized and compared with those of other mmWave semiconductor devices. Section 3 describes the detailed LNA design with the discussion of the series inductor-based stability enhancement technique. Experimental results are presented in Section 4. Finally, Section 5 concludes the paper.