Preface 



Monographs usually present scholarly summaries of a well-developed 

 field. In keeping with the philosophy of the new series of Research 

 Monographs, however, this monograph was written to present a piece of 

 relatively recent work in a comparatively undeveloped field. Such work 

 might normally be expected to appear in a series of journal articles, and 

 indeed originally the authors followed this method of presentation. As 

 the subject developed, however, a rather general approach to the problem 

 became apparent which both simplified and unified all the prior research. 

 Space limitations in the journals made it impossible to publish in that 

 medium a really suitable picture of the whole development, and this 

 circumstance led the authors to take advantage of the present Technology 

 Press Research Monographs. 



The principal motivation for this work arose from the obvious desir- 

 ability of finding a single quantity, a tag so to speak, to describe the 

 noise performance of a two-terminal-pair amplifier. The possibility of 

 the existence of such a quantity and even the general functional form 

 which it might be expected to take were suggested by previous work of 

 one of the authors on microwave tubes and their noise performance. 

 This work showed that noise parameters of the electron beam set an 

 ultimate Hmit to the entire noise performance of the amplifier that 

 employed the beam. In the microwave tube case, however, the findings 

 were based heavily upon the physical nature of the electron beam, and 

 it was not immediately clear that a general theory of noise performance 



