2
Chapter 2
Theory of Operation
Traveling Wave Viewpoint
The easiest way to visualize Thruline operation is from a travelling wave
viewpoint. In transmission lines the voltages, currents, standing waves, etc., on
any uniform line section result from the interaction of two travelling waves:
The forward wave (and its power) travels from the source to the load.
It has RF voltage E
f
and current I
f
in phase, with E
f
/ I
f
= Z
o
.
The reflected wave (and its power) originates by reflection at the load
and travels from the load back to the source. It has an RF voltage E
r
and current I
r
in phase, with E
r
/ I
r
= Z
o
.
Each wave is mathematically simple and has a constant power:
Note:
Z
o
is the characteristic impedance of a uniform line section.
For useful lines it is usually a pure resistance of 50
. The RF circuit
of the Bird 43 is a length of uniform air line with Z
o
= 50
.
W
f
WattsForward
E
f
2
Z
o
I
f
2
Z
o
E
f
I
f
=
=
=
=
W
r
WatssReflected
E
r
2
Z
o
I
r
2
Z
o
E
r
I
r
=
=
=
=
