A substantial amount of reflected energy will radiate out through the same aperture (e.g., window, door, etc.) through which the incident energy came. Determination of the reflectivity level in an enclosure is understood by considering the simple case of a direct-path plane-wave signal ED (constant magnitude and phase) combining with an interfering plane-wave signal ED arriving at the test point under an angle $ (see Figure 3). A maximum is produced by two wave fronts whose phases differ by 2k. The maximum amplitude is The spatial periodicity "p" depends upon the angle between the interfering wave fronts. The resulting field will form a standing-wave pattern with field maxima twice the value of the incident wave if a once-reflected signal does not suffer losses, that is The field strength Emax and the periodicity p are altered when several wave fronts with different reflection angles interfere. Two examples of superimposing space harmonics are depicted in Figure 4. 3.1. Reflective Losses from Metals A surface with high reflectivity for the SPS microwave radiation consists typically of metal, of wire mesh (mesh size < 1.5 cm), or of a multilayer arrangement of low-loss dielectric plates (Harvey, 1970), whereby the dielectric multilayer reflector is unlikely to occur in habitable structures. Metals reflect microwaves and conduct field-induced currents. A very small fraction of the incident energy is absorbed by the metal surface. The loss in one reflection is (f in GHz) where the skin depth 6 in pm is the distance the field strength has fallen to 1/e = 0.368 of its surface value. In nonmagnetic metals,
RkJQdWJsaXNoZXIy MTU5NjU0Mg==