The usage of Ka-band technology offers numerous new applications, including 5G mobile communications, fixed wireless access (FWA), low earth orbit (LEO) satellites, and electronic warfare. However, the susceptibility of Ka-band receivers to interference requires the use of highly linear and robust low noise amplifiers (LNAs) in these systems.

Microscope photograph of the fabricated LNA. Credit: Ferdinand-Braun-Institut GmbH, Leibniz-Institut für Höchstfrequenztechnik

In a recent study conducted by the Joint Lab BTU-CS – FBH Microwave, researchers have presented a highly robust 28-32 GHz GaN-based LNA. The LNA was designed using a GaN high electron mobility transistor (HEMT) with a gate length of 150 nm and a 4 x 50 μm gate width on a semi-insulating SiC substrate.

Additionally, stress tests were conducted on three LNA sample. The results indicate that one LNA burnt out after reaching an input power of 34.3 dBm at 30 GHz CW, while the other two LNAs survived, withstanding the highest applied input power of 34.4 dBm. The surviving LNAs were measured after approximately 2 hours and exhibited a positive threshold shift, as well as a slight degradation in small-signal gain and noise figure . After readjusting the bias current, the measured small-signal gain and noise figure returned to values close to the pre-stress conditions, demonstrating the undamaged state of the LNAs.

This study demonstrates the survivability of FBH GaN-based LNAs under high-stress conditions in Ka-band receivers. Furthermore, it highlights the potential of FBH GaN HEMT technology in the mm-wave range. Compared to GaAs LNAs, GaN LNAs offer high ruggedness, eliminating the need for input protection circuits and improving the receiver's noise figure. Additionally, the use of GaN HEMT technology enables the development of compact and cost-effective single-chip integrated RF frontends, which can facilitate applications such as massive MIMO.

The research described in this paper is funded by the German Ministry of Education and Research (BMBF) through the ForMikro-LeitBAN program (grant no. 16ES1112) and the project reference 16FMD02 (Forschungsfabrik Mikroelektronik Deutschland).

Source: Publication: S. Haque, C. Andrei, H. Yazdani, and M. Rudolph, "On the Survivability of a 28–32GHz GaN Low Noise Amplifier," 18th European Microwave Integrated Circuits Conference (EuMIC), Berlin, Germany, 2023.