A New Design Technique for Power Amplifiers Operating Close to Unit-Current-Gain Cutoff Frequency

In this paper, we presented the design and implementation of a two-stage power amplifier (PA) operating at a frequency close to 90% of the unit-current-gain cutoff frequency $(f_{T})$. Instead of the conventional configuration where inductors and capacitors were adopted as the matching components, a simple yet novel topology composed of transmission lines as matching components was proposed. Optimum choice of the transmission line parameters minimized the matching loss which in turn pushed the operating frequency toward the limit. Implemented in standard 0.15$-\mu$mGaAs pHEMT technology, the measurement results exhibited good performance making such approach feasible for PA designs beyond millimetre-wave frequencies.