TABLE OF CONTENTS Microwave optics refers to a collection of ray-tracing methods. In previous chapters, the fundamental mechanism of specular reflection (i.e., a reflection that obeys Snell s law) has been used to justify concepts such as image theory. Ray tracing has an advantage over the numerical methods of Chapters 3 and 4 in that the propagation of rays gives physical insight into scattering behavior. For example, when a plane wave is reflected from an interface, it is easy to see that the maximum reflection will occur when the observation direction satisfies Snell s law.
Geometrical optics (GO)1 3 is a version of ray tracing that has been used for centuries at optical frequencies to design systems of lenses (telescopes, microscopes, etc.). It works well at optical frequencies because the lens dimensions are much larger than a wavelength and, thus, the interaction of the wave with the lens becomes a localized phenomenon. Under these circumstances, the reflected ray appears to originate from a single point on the surface called a specular point.
There are several problems with geometrical optics, and they are more pronounced as the scattering body becomes smaller. For example, a reflection from an infinite PEC surface would result in a reflected field observed only when ? r = ? i and in a zero field elsewhere. This agrees with the physical optics result for the same situation; an infinite surface gives a scatter pattern that has zero beamwidth. Forafinite surface, PO yields scattering patterns...
