# An MMIC LNA for Millimeter-Wave Radar and 5G Applications with GaN-on-SiC Technology
###### Abstract  
This paper presents a monolithic microwave integrated circuit (MMIC) low noise amplifier (LNA) that is compatible with n257 (26.5-29.5 GHz) and n258 (24.25-27.5 GHz) frequency bands for fifth-generation mobile communications system (5G) and millimeter-wave radar. The total circuit size of the LNA is \(2.5\times 1.5\) mm2. To guarantee a trade-off between noise figure (NF) and small signal gain, the transmission lines are connected to the source of gallium nitride (GaN)-on-SiC high electron mobility transistors (HEMT) by analyzing the nonlinear small signal equivalent circuit. A series of stability enhancement measures including source degeneration, an RC series network, and RF choke are put forward to enhance the stability of designed LNA. The designed GaN-based MMIC LNA adopts hybrid-matching networks (MNs) with co-design strategy to realize low NF and broadband characteristics across 5G n257 and n258 frequency band. Due to the different priorities of these hybrid-MNs, distinguished design strategies are employed to benefit small signal gain, input-output return loss, and NF performance. In order to meet the testing conditions of MMIC, an impeccable system for measuring small has been built to ensure the accuracy of the measured results. According to the measured results for small signal, the three-stage MMIC LNA has a linear gain of 18.2-20.3 dB and an NF of 2.5-3.1 dB with an input-output return loss better than 10 dB in the whole n257 and n258 frequency bands. m 2023 2  
moving up to millimeter-wave (mmWave), a high data rate, wide channel bandwidth, and low latency can be achieved simultaneously [3; 4]. In addition, the 5G mmWave frequency bands n257 and n258 may receive global prioritization. Such regulations are distinguished from the lower, overcrowded sub-6 G frequency range and cater for the requirements of high data rate wireless communications in today's world. Millimeter-wave radar systems [5; 6] are usually divided into Frequency Modulated Continuous Wave (FMCW) radar and Doppler radar. Considering the relatively higher maximum equivalent isotropic radiated power (EIRP) allowed in the standard and the relatively narrower bandwidth requirement compared with the Doppler radar, FMCW radar is more attractive for millimeter-wave radar applications. Based on the FMCW radar system, the LNA is one of the most pivotal active components, which highly determines the overall NF of the receiver. To meet the requirements of dynamic range and sensitivity of the millimeter-wave radar system, we need to design an MMIC LNA with low NF, reasonable gain, and broadband bandwidth, which further introduces great challenges in finding a trade-off between these performances [7]. Compared with gallium arsenide (GaAs), GaN-based materials can effectively reduce the number of transceivers and circuit size while providing higher power handling ability and higher cutoff frequency [8; 9; 10; 11]. Due to the high expenditure of using homogeneous materials, heterogeneous materials are mostly used for GaN technology, including GaN-on-Si and GaN-on-SiC. Since the thermal conductivity of GaN-on-SiC is three times higher than that of GaN-on-Si, devices can operate at higher voltages and higher power densities. GaN-on-SiC HEMT devices have become one of the best candidates for mmWave power amplifiers (PAs) owing to their distinct benefits [12; 13; 14; 15]. Although many studies primarily focus on analyzing the power performance of GaN HEMT, its noise performance [16; 17; 18; 19] has also attracted increasing attention. In fact, GaN HEMTs achieve considerable microwave noise performance comparable to gallium arsenide (GaAs). Additionally, the excellent robustness of GaN transistors and the ability to integrate PAs and LNAs in the same epitaxial material without the need for receiver protection circuits have sparked great interest in GaN technology for low-noise applications. The RF front-end module, which integrates LNA, PA, and switch, has lower package loss and is more cost-effective, resulting in reduced size.