World War II brought about the first widespread utilization of microwaves for practical purposes.
By microwaves we generally mean electrical energy of wavelengths from 12 to 1.2 cm. corresponding to frequencies of 2500 to 25,000 megacycles per second.
It was the use of this radiation that made precision radar possible.
After initiation by the British the tremendous task of developing microwave apparatus was left to the laboratories in the United States and to the engineers of many concerns engaged in manufacturing.
By the end of 1945 sufficient theory had been developed and sufficient empirical data had been collected to make possible the manufacture of microwave transmission equipment for almost any application.
In fact, a quantity of components was available on the American market comparable to the variety produced for any other communications circuits.
Likewise, a complete line of measuring instruments and test equipment was being manufactured.
Prior to 1942 it would have been impossible to purchase or procure by special order any microwave components whatsoever.
Therefore, it was during the four years, 1942 to 1945, that all of the research and development work necessary to achieve the practical utility of this field of electricity was carried on.
Evaluated on a basis of man hours of research time the bulk of microwave development was centered at the M. I. T. Radiation Laboratory.
Contributions to the subject were made available from four sources.
Physicists such as N. H. Frank, J. C. Slater and L. J. Chu provided theoretical treatments.
Components groups in the Laboratory devoted exclusively to the development of particular items, for example, T-R boxes, contributed volumes of measured data.
Systems engineers provided practical designs for use in radar equipment.
-1 procurement group labored patiently with experimental runs of components subcontracted to outside manufacturers.
These activities within the Laboratory provided the basis for a treatise on microwave transmission circuits embodied in Volume 9 of the M. I. T. Radiation Laboratorv Series.
Although George L. Ragan acted as editor, there were seven contributing authors comprising key men in this field.
The specialties of these men include transmission circuit theory, materials and construction techniques, components such as various types of lines and couplings, rotational joints, tuners, power dividers, switches and microwave filters.
The mathematics employed in the book utilizes primarily the concepts of impedance making illustrative use of the admittance diagram or Smith chart.
The book is filled with plotted data on transmission characteristics of waveguides containing various geometrical configurations.
The section on microwave filters makes use of familiar communications circuit analysis techniques with the proper adjustments necessary for the treatment of microwave plumbing.