13-11-2012, 05:34 PM
ANTENNAS AND WAVE PROPAGATION
ANTENNAS AND WAVE.pdf (Size: 1.16 MB / Downloads: 96)
Propagation Mechanism
Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal
Refraction - When there is a transition from one medium to another.
Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave.
Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less
Perfect conductor & Dielectric
Perfect conductors reflect with no attenuation
Dielectrics reflect a fraction of incident energy
•Reflection induces 180 phase shift
Refraction properties
When wave enters a region with a higher dielectric constant ( a lower propagation velocity) it bends toward the normal.
Critical angle. (large incident angle + wave travels to area of low dielectric constant. Extreme case is total internal reflection)
Fresnel Zones
Alternate zones differ in phase by 180
Line of sight (LOS) corresponds to 1st zone
If LOS is partially blocked, 2nd zone can destructively interfere (diffraction loss)