b. The dielectric loss of air is so small that we can ignore it. Air
is the only dielectric contained in waveguide; therefore, waveguide has
negligible dielectric loss.
c. The third kind of loss most RF transmission lines have is radiation
loss.
14. Why waveguide does not have radiation loss.
a. You know that current flow in a conductor sets up a magnetic field
at tight angles around the conductor.
The magnetic field produces an
electric field, and both these fields are radiated into space.
This
radiation is a loss of energy except in applications where we want to
radiate energy out into space, such as with an antenna.
b. You see then, that all unshielded transmission lines radiate some
energy. We call this loss of energy radiation loss.
c. Energy traveling through waveguide is contained within the walls of
the waveguide. All current flow is on the inside surface of the walls, and
no energy can go out into space. Hence, waveguides have no radiation loss.
d. You have just learned how transmission line losses compare with the
slight losses of waveguide. Table III shows this comparison and also shows
the frequency bands for waveguide and the other various types of
transmission lines.
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