A Single Stage Q-band GaN HEMT Amplifier Which Has Gain over the Fmax

This study demonstrates an single stage amplifier with a gain between 37 GHz and 44 GHz, 6.9 dB at 40.1 GHz, using a GaN HEMT, which has an fmax of only 41 GHz. A transistor amplifier is usually designed at a frequency reasonably less the fmax because it is the frequency limit where unilateral gain becomes unity; theoretically, no amplification can be realized over this frequency. To overcome this theoretical limit, the novel method was developed to control the standing wave distribution in the gate finger. Through this method, the potential gain of the transistor increased around fmax, and moreover, the fmax value itself increased significantly. The GaN HEMT in this study is demonstrated to increase the fmax from 41 GHz to 70 GHz. Furthermore, by using this method, an amplifier which has gain over the fmax frequency is realized.