An efficient 0.6-4.2 GHz GaN-HEMT power amplifier based on Klopfenstein taper is proposed in this letter. A method based on source-pull/load-pull simulation has been used to find the optimum source and load impedances across the broad band. Then the Klopfenstein taper is studied and adopted for the output matching circuit design to achieve broadband performance. The measured results show that our proposed power amplifier has a fractional bandwidth of 150%, with saturated output power ranging from 39.45 to 42.32 dBm, power added efﬁciency from 45.1% to 64.8%, and over 9 dB gain at the whole working band of 0.6-4.2 GHz. The fabricated power amplifier can cover most of the wireless communication frequency bands.
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