With the rapid development of the modern radio systems, communications equipment and radar performance have achieved unprecedented progress. As one of the most important and largest power consumption modules, the power amplifier directly affects the performance of a radio system[1, 2]. Power devices based on Si, GaAs or other materials are limited by gain, bandwidth, thermal stability and output power density. When the required power is reached, the size of the power amplifier is relatively large. The power amplifier cannot achieve high efficiency with the use of GaAs devices[3, 4]. It is gradually unable to meet the requirements of current communications and radar equipment for the high power and high efficiency. So the power amplifier is still under constant development. For example, the power amplifier MMRF1016H in this band of NXP, working in the pulse (100 $\mu $s, 10% duty cycle) state, the output power is 600 W and the drain efficiency is about 60%.
In recent years, the third generation of semiconductor materials, such as the GaN, SiC, which is the representative of the wide band gap semiconductor materials that can withstand higher electric field, has higher electron mobility and high thermal conduction efficiency. So it can work under high voltage conditions, with smaller parasitic parameters, achieve high power and wide bandwidth in a smaller volume. When the GaN material is used in the production of a power amplifier, it is necessary to meet the requirements about gain, efficiency, power, flatness and others, and the most important thing is stability. GaN HEMT has a higher power density, so it is more prone to instability in low frequency[7, 8].
To eliminate the instability of GaN power amplifier at low frequency, the RC-LC stability network structure is proposed, by connecting the stability network in front of the input-matching network. The RC-LC network forms a more perfect band-pass filter than the traditional RC structure. The inductor in the stability network adds a first-order filter and the stability circuit leads to a mismatch out of the band. Which greatly reduces the gain in low-frequency band and significantly increases the stability of the circuits.