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Old March 10th 04, 03:34 PM
Cecil Moore
 
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Richard Harrison wrote:
Seems to me there`s no magic. The waves just do what they must.


Reckon why some people believe that wave energy is allowed to change
directions at the load but not allowed to change directions at the
match point?

One of the problems in the field of RF (that the optics people don't
have) is the effective reflection coefficient Vs the physical
reflection coefficient. I have never heard an optics engineer say,
"Since reflections are eliminated at the thin-film surface, the
effective index of refraction of the thin-film is 1.0." The optics
reflection coefficient doesn't change with the magnitude of reflected
energy. It is always (n2-n1)/(n2+n1) where 'n' is the index of refraction.

Yet RF engineers will say, "Since reflections are eliminated at the
50 ohm to 450 ohm impedance discontinuity, the reflection coefficient
is zero." Why isn't the reflection coefficient always (Z2-Z1)/(Z2+Z1)
as it is in the field of optics?

Note: [(Z2-Z1)/(Z2+Z1)]^2 = [(n2-n1)/(n2+n1)]^2

The term on the left side of the equation is the RF power reflection
coefficient. The term on the right side of the equation is the
Reflectance (the irradiance optical reflection coefficient). Irradiance
is energy per unit time per unit area and is equal to power per unit
area. Thus the irradiance of a confined laser beam is equivalent to
power in a confined transmission line.
--
73, Cecil http://www.qsl.net/w5dxp



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