A 0.7–4.9GHz Multi-Octave Broadband Power Amplifier Based on the Bandwidth Extension of the Quarterwave Transmission Line

This paper presents a broadband impedance matching technique for RF power amplifiers based on a single quarterwave transmission line (QTL) used with multiple resonance circuits. It is demonstrated how the shunt and series resonance circuit can each operate to extend the bandwidth of a QTL, respectively. Furthermore, simulated results are shown that when both the series and shunt resonance circuits are used compositely, the bandwidth of the QTL can be extended even to multi-octave frequencies. In practice, the proposed topology can be simply realized by utilizing essential circuit components of a typical power amplifier which uses the shunt inductor for drain dc supply, and the series capacitor for dc blocking. To verify the proposed bandwidth extension method, a power amplifier was designed at the frequency band of 0.7–4.9 GHz with a 10 W GaN-HEMT packaged transistor. Measurement results over-achieved the targeted 10 W of output power at the entire frequency band of 0.7–4.9 GHz for a fractional bandwidth of 150%, while exhibiting drain efficiency of 48.4–71.4%.