# An MMIC LNA for Millimeter-Wave Radar and 5G Applications with GaN-on-SiC Technology
## 3 Implementation and Measurement  
The micrograph of the fabricated three-stage LNA is shown in Figure 10, where the effective dimension marked in the red box is 2.5 \(\times\) 1.5 mm\({}^{2}\). The die is fabricated using 0.15 \(\upmu\)m GaN-on-SiC technology and has a larger footprint than necessary. This is achieved entirely to match the die area of other MMIC modules in the multi-project. The GaN HEMT is supplied with a 5 V drain bias voltage through the VD, and its \(-\)1 V source bias voltage is supplied through the VG, respectively. RF signals enter from the RF\({}_{\text{in}}\) port and exit from the RF\({}_{\text{out}}\) port.  
Figure 11 illustrates a set of equipment block diagrams for small signals, including S-parameters and NF [2; 36; 37]. A 5V supply voltage, provided in pulse mode by the RIGOL DP832A, is used for the drain bias. This adjusts the gate bias voltage to obtain the same quiescent current. The small signal performance of the MMIC LNA is measured using the Keysight PNA Vector Network Analyzer N547B, which operates within the n257-n258 frequency range. And the simulation results were performed by using ADS2020 software with a GaN HEMT design kit.  
Figure 10: Micrograph of the proposed LNA (dimensions: 2.5 \(\times\) 1.5 mm\({}^{2}\)).  
Figures 12 and 13 present the measured and simulated S-parameter results of the proposed MMIC LNA from 20 GHz to 35 GHz. The measurements demonstrate that the implemented LNA exhibits a linear small signal gain (S21 refer to Figure 12) from 18.3 dB to 20.2 dB. Additionally, the reflection coefficients (S11 and S22, as shown in Figure 13) remain below less \(-\)10 dB across the frequency range of 24.25-29.5 GHz. The measured reverse isolation (S12, as shown in Figure 13) of the fabricated MMIC LNA is better than \(-\)40 dB. Figures 12 and 13 indicate that the test results exhibit good agreement with the simulation results, albeit with a certain degree of degradation in both cases.  
Figure 11: Block diagram of equipment for measurement of S-parameters and NF.  
Figure 12: Measurement and simulation results of S21 for the fabricated MMIC LNA.  
The measured NF response of the proposed LNA in Figure 14 is 2.5-3.1 dB in the interesting frequency band of 24.25-29.5 GHz, which is about 0.7 dB worse than the simulated result. It is customary for the test results of noise figure (NF) to exhibit degradation compared to simulation performance. This discrepancy can be attributed to the presence of unaccounted parasitic effects during the simulation process.  
As shown in Figure 15, measurements of k and b indicate that the LNA is stable over the entire frequency band, thanks to a series of strategies adopted in this design to improve stability.  
Figure 14: Measurement and simulation results of NF for the fabricated MMIC LNA.  
Figure 13: Measurement and simulation results of S-parameters (S11, S22, and S12) for the fabricated MMIC LNA.  
Table 1 summarizes the performance comparison of some related LNAs with different processes, which demonstrates the advanced performance of this designed MMIC LNA. As can be seen from Table 1, although this design is not the best in terms of bandwidth, gain, noise factor, power consumption, and other performance metrics, it still exhibits advanced characteristics based on the aforementioned performance. In comparison to designs utilizing the same GaN process, this design not only achieves lower NF but also consumes less power. Moreover, when compared to designs using GaAs and CMOS processes, this design demonstrates significant advantages in terms of small signal gain and NF.