The Load Modulated Balanced Amplifier Slides

Quadrature-balanced amplifiers hold a revered position in the historical development of broadband microwave amplifiers up to 20 GHz and beyond, because they replaced unreliable traveling wave tubes (TWTs) with solid-state equivalents. After declining in popularity when monolithic microwave integrated circuits (MMICs) entered the market, they are now becoming useful again due to research at Cardiff and University of Colorado, Boulder showing a surprising and counter-intuitive property that allows active load modulation of the output match presented to the balanced transistors. This has enabled broadband matching network design to break away from conventional constraints and has opened up application avenues in high efficiency RF power amplifier (RFPA) design, both in telecommunication and electronic countermeasure (ECM) bands.