An Optimal Dual-Band Output Matching Method for a Power Amplifier

This article presents an optimal dual-band output matching method for a power amplifier (PA). The proposed matching method utilizes series and parallel resonance to transform a frequency-dependent optimum load impedance of a transistor to 50 $\Omega $ at target frequencies. The selectable range of a low-frequency is analyzed when a high-frequency is selected. A 2.45-/5.8-GHz PA was designed and fabricated on the Rogers 5880 substrate, utilizing the Wolfspeed gallium nitride (GaN) high electron mobility transistor (HEMT) of CGH40006s. The PA achieves a small signal gain ( $S_{21})$ of 13.9 dB at 2.45 GHz and 10.5 dB at 5.8 GHz. At the 3-dB compression point, the output power (OP $_{\mathrm{3\,dB}})$ is measured at 38.4 dBm for 2.45 GHz and 38.6 dBm for 5.8 GHz, while the corresponding drain efficiency (DE $_{\mathrm{3\,dB}})$ is 71% at 2.45 GHz and 59.7% at 5.8 GHz. Furthermore, to verify the effectiveness of the matching method in the millimeter-wave region, a 28-/48-GHz PA was implemented using a 0.15- $\mu $ m gallium arsenide (GaAs) pseudomorphic HEMT (pHEMT). The PA has $S_{21}$ of 22.6 dB at 28 GHz and 15.5 dB at 48 GHz. The OP $_{\mathrm{3\,dB}}$ was 19.1 dBm at 28 GHz and 18.6 dBm at 48 GHz, with the power-added efficiency (PAE $_{\mathrm{3\,dB}})$ corresponding to 37.3% and 28.5%.