Broadband high power amplifiers for instrumentation

Microwave power amplifiers designed for instrumentation are characterized by a range of properties which sets them apart from other types of applications. Broad bandwidths are generally desired, and so are low noise (both in amplitude and phase), high stability, and low spurious responses. High reliability is a plus for most applications, but in this case ease of repair is also quite significant and so is the ability to maintain some working capability in case of failure (the so-called graceful degradation). When a measurement is performed by transmitting and receiving a signal, the ability to turn off and on the amplifier at a fast rate may dramatically improve the instrument sensitivity and fast pulsing can be a very desirable option. All of these characteristics are much more favorable in Solid State Power Amplifiers (SSPAs) than in traveling wave tubes (TWTs) and the former are generally the preferred choice unless an unusually high power output is required. Traditionally, the requirements for power in instrumentation used to be fairly modest. Not anymore: in the last ten to fifteen years the demand for measurements at high power levels has grown dramatically. But so have the power levels available from SSPAs, and, at the same time, the cost per unit power has been decreasing to a level comparable with TWTs, so that, when the much longer life is taken into account, the solid state alternative is generally both feasible and cost effective.