[Antennas] Maximum Power Transfer Theorem

[Robert Lay]

For those interested in Conjugate Match theory and the Maximum Power
Transfer Theorem, I have made extensive improvements in my article on the
subject which is now available in PDF form in its second revision at the
following URL:

www.qsl.net/w9dmk/MPTT.pdf

Comments are welcome.

A brief discussion of the relevance to amateur radio and antennas in
particular follows:
In order to avoid reflections and standing waves on transmission lines, it
is recognized that a conjugate match should exist between the antenna and
the transmission line. In those instances in which the conjugate match is
successfully realized, any mismatch at the transmitter end of the line is
irrelevant for most purposes. However, when there is a mismatch at the
antenna end, then any mismatch at the source (transmitter) exacerbates the
problem by causing an additional reflection at that end. The result is that
there are reflections traveling in both directions. That in itself is of no
great concern with amateur radio transmissions but can cause problems in
such applications as microwave radio relay repeaters that are carrying
several hundred channels of telephone calls. In amateur radio the concerns
regarding a mismatch at the source end usually revolve around questions
about how the transmitter final amplifier stage might be affected by the
energy arriving as reflections from the antenna mismatch. For example, under
conditions of high VSWR on the line, is the final amplifier stage subjected
to any unusual stresses? The subject article does not get to that question
directly but instead lays the groundwork for further work in that or other
areas of interest. Specifically, the subject article focuses on the Maximum
Power Transfer Theorem, which includes the concept of the Conjugate Match,
and explains what really goes on when a power-limited device transfers power
to a load under conditions of varying load impedance. Analyses of both
turbo-electric and all-mechanical systems are presented. A follow-on article
on the subject of Class-B Linear Amplifiers is in progress and is expected
to be published before the end of March 2004.

Bob Lay (W9DMK), Dahlgren, VA
w9dmk@crosslink.net
http://www.qsl.net/w9dmk