6.1 Electromagnetic Theory Fundamentals

When analyzing electrical circuit parameters one usually analyses the effect of a current flow through a certain impedance that sets up a voltage across the element. When considering antennas it is more useful to analyze the effects in terms of the electric and magnetic field vectors since the wavefront, which is generated by an antenna, travels as an electromagnetic field. An electromagnetic (EM) wave has two orthogonal components: an electric field and, perpendicular to this, a magnetic field. These two fields can both he considered sinusoidally varying signals perpendicular to each other, both normal to the direction of propagation, as shown in Figure 6.1.

Figure 6.1: Electromagnetic wavefront.

In an EM wave, the electric and magnetic fields interact with one another. A changing magnetic field will induce an electric field and a changing electric field will induce a magnetic field. The wavefront is the imaginary line that is drawn through the plane of constant phase. A plane wave is one that has a plane wavefront. A uniform wavefront is one that has constant magnitude and phase. The magnitude of the electric and magnetic field vectors are thus equal...