In this paper, a high-efficiency compact power amplifier is designed and fabricated with a 0.25 μm GaN high electron mobility transistor (HEMT) to meet the demands of a high integration level and high efficiency for microwave wireless power transfer (WPT) systems. The proposed power amplifier (PA) is implemented using an internally matched method to achieve a compact circuit size. The output second and third harmonic impedances can be optimized through output matching circuits, eliminating the need for additional harmonic matching networks. This approach simplifies the design of matching circuits and reduces the circuit size. Furthermore, the input third harmonic has been controled for improving the efficiency of DC-to-RF conversion. The total size of the proposed PA is $13.4 \times 13.5$ mm². The test results obtained from the continuous wave (CW) testing indicate that the output power of the power amplifier at 2.45 GHz reaches 43.75 dBm. Additionally, the large-signal gain is measured at 15.75 dB, and the power-added efficiency (PAE) achieves a value of 78.5%.

This study presents an ultra-wideband (UWB) and high-power amplifier (HP A) that employs a two-stage single-transistor driven distributed amplifier (SDDA) architecture to improve the linearity. The gate-bias optimization method for cascaded amplifiers is proposed based on nonlinear cancellation theory. By optimizing the bias and thereby changing the higher-order transconductance of transistors in the HP A, a third-order in-termodulation sweet spot (IM3-S) can be generated and shifted toward the saturation output region, which can improve the linearity with high output power and high efficiency in a UWB frequency. A monolithic microwave integrated circuit (MMIC) UWB-HP A was designed to validate the proposed method utilizing an in-house 0.25 µm gallium nitride (GaN) process. The SDDA demonstrates an output power exceeding 10 W across 0.03 GHz to 6 GHz and a power-added efficiency (P AE) greater than 41%. The two-tone measurement results indicate that, when the IM3-S is shifted to 0.9 dB output-back-off (OBO) at 2.6 GHz, the 1M3 reaches −33.8 dBc with an output power of 39.5 dBm and a P AE of 41%. At 5.6 GHz, after shifting the IM3-S to 2.2 dB OBO, the 1M3 reaches −35.6 dBc with an output power of 37.7 dBm and a PAE of 52%. The ratios of output third-order intercept point to direct current power (OIP3/Pdc) reach state-of-the-art values of 39 and 128 at 2.6 GHz and 5.6 GHz, respectively. The results of this study will be helpful for high linearity design of GaN UWB-HP As.

In this paper, a GaN high-electron-mobility transistor (HEMT) compact high-power wide-band power amplifier with an operation frequency from 0.8 GHz to 2 GHz is proposed. In order to realize a compact design, an internally matched method is employed. A wide-band matching strategy with an LC network and a multi-stage wide-band power combiner/divider is introduced in this design to achieve a wide bandwidth. A power combination structure is applied to have high output power. Wire-spiral inductance and film capacitors are employed to construct the compact matching network. The equivalent inductance of the bonding wire is also involved in the matching network. Experimental results show that the PAE (power-added efficiency) during the whole operation’s bandwidth (0.8 GHz to 2.0 GHz) is from 40% to 57%. The output power can reach from 48.3 dBm to 49.8 dBm with a circuit size of $30.8\times 27.4{\mathrm{mm}}^2$.