While there are many excellent books available on fundamental and applied
electromagnetics, most introduce operator concepts in an ad hoc manner, and few
discuss the subject within the general framework of operator theory. This is in
contrast to quantum theory, where the use of operators and concepts from
functional analysis is common. However, casting electromagnetic problems in
terms of operator theory produces useful insights into the mathematical
properties and physical characteristics of solutions. For instance, the commonly
used modal expansion of fields in waveguides are immediately justified upon
identifying the differential operators as being of the appropriate
Sturm-Liouville type. As another example, existence, uniqueness and solvability
of integral formulations