Multi-Purpose Thruline Wattmeter RF Power Analyst
5
stationary, the coupling currents produced from the waves of one direction will
add in phase, and those produced from waves of the opposite direction will
accordingly subtract in phase. The additive or “arrow” direction is assigned to
the forward wave.
The electrical values of the element circuits are carefully balanced and designed
so that current from the reverse wave will cancel the other almost completely.
The result is directivity always higher than 25 dB, which means that the element
is highly insensitive (nulled) to the REVERSE direction wave. Being highly
directional, the Thruline element is sensitive (at one setting) only to one of the
traveling waves that produce standing waves by interference. Thruline
Wattmeter measurements are, therefore, independent of position along
standing waves.
Figure 4 Readings with Various Envelopes
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