OVERVIEW

Dr. Wolfgang J.R.Hoefer is a well known professor and research engineer in the field of electromagnetic engineering and microwave devices. I wish to thank him for his effort and valuable contribution.

Dr. K.Feher

Inevitably, the communications systems engineer will encounter microwave amplifiers of some kind when designing or evaluating a microwave system. In a typical digital microwave system the amplifiers contribute more to the overall P(e) performance and system gain (described in the next chapter) than up-converters, down-converters, oscillators, or other active elements. In this chapter we therefore describe the most common types of microwave amplifiers; their characteristics, specifications, and limitations are presented, and a survey of the state of the art is included. Our purpose in this chapter is to enable the systems engineer to understand the significance of amplifier specifications, to evaluate such a product, and to specify the desirable characteristics of an amplifier required for a given system.

The requirements imposed on microwave amplifiers depend on their purpose. Two fundamental types of amplifiers can be distinguished: the microwave power amplifier and the small-signal amplifier.

The power amplifier must deliver a microwave signal of sufficient power to produce an easily detectable output at the end of a transmission channel. This signal should be produced with maximum efficiency and reliability and with minimum distortion. In contrast, the small-signal amplifier must increase the power of a weak signal sufficiently for further processing. In this application,...