Fundamentals

The science of electromagnetic compatibility has been in exis­tence for several decades. As an art, it goes back much further, perhaps to the time of Edison when he was just beginning to experiment with practical electrical devices. I am sure that with some of his more sophisticated devices undesired interac­tions took place because of inadequate shielding or filtering. Certainly, with the advent of radio, incompatibility problems occurred as a result of the poor quality of transmitters and receivers. Perhaps the first formal recognition of electromag­netic compatibility problems occurred when the telephone and power companies found they had mutual coupling problems when their lines were carried on the same utility poles. Later on, the increasing use of the radio spectrum called for formal controls administered by departments in the post, telephone, and telegraph offices in many countries, or through the Feder­al Communications Commission in the United States.

The Method of Moments has become one of the most powerful tools in the RF engineer’s arsenal. In this chapter, we make the transition from theory to practice, first by attempting to compute the characteristics of a “short dipole” by hand, and then by demonstrating that a computer can do that in just a few seconds.

It is time to put these equations to work by computing the radiation from a simple structure, a short wire element.

In the preceding chapters we have derived Maxwell’s Equations and expressed them in their “integral” and “differential” form. In different ways, both forms lend themselves to a certain intuitive understanding of the nature of electromagnetic fields and waves. In this installment, we will express Maxwell’s Equations in their “computational form,” a form that allows our computers to do the work.