This letter presents a high-power amplifier (HPA) monolithic microwave integrated circuit (MMIC) based on the 0.25- $\mu$ m gallium nitride (GaN) high-electron-mobility transistor (HEMT) process. An elliptic filter output matching network (MN) and a matching circuit design method based on the combination of port impedance model (PIM) and load pull are proposed, which can achieve high harmonics suppression across 7–13 GHz using a reactive matching (RM) technique. The three-stage GaN PA achieves a minimum output power of 44.7 dBm and a peak output power of 46.3 dBm at 7.5 GHz. The power-added efficiency (PAE) is more than 34.4%, with a peak PAE of 39.0% at 9.5 GHz. The second harmonic suppression (HS2) reaches more than 22.5 dBc. The PA chip occupies an area of 4.8 $\times$ 3.0 mm $^{2}$ .

This paper presents an ultra-wideband transformer feedback (TFB) monolithic microwave integrated circuit (MMIC) power amplifier (PA) developed using a 0.25 μm gallium nitride (GaN) process. To broaden the bandwidth, a drain-to-gate TFB technique is employed in this PA design, achieving a 117% relative −3 dB bandwidth, extending from 5.4 GHz to 20.3 GHz. At a 28 V supply, the designed PA circuit achieves an output power of 25.5 dBm and a 14 dB small-signal gain in the frequency range of 6 to 19 GHz. Within the 6 to 19 GHz frequency range, the small-signal gain exhibits a flatness of less than 0.78 dB. The PA chip occupies an area of 1.571 mm². This work is the first to design a power amplifier with on-chip transformer feedback in a compound semiconductor MMIC process, and it enables the use of the widest bandwidth power amplifier on-chip transformer matching network.