______________________________________________
HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
167
The output side of this circuit (the left side of Figure 7-3, within dotted box) including
the amplifiers) functions like a conventional Wilkinson combiner, it is the right side that
is of interest here. At the right side, all of the 1/4 wavelength, 50 ohm transmission lines
are joined together. Since each line feeds the same voltage to this junction, it appears as
a virtual open during normal operation of this combiner. 1/4 wavelength away from this
virtual open circuit, the 50 ohm transmission lines present a short circuit to reject loads
(R1 through R4), placing them at virtual ground. The 1/4 wavelength, 50 ohm lines that
connect each reject load to its amplifier appear as an open circuit to the amplifier. This
makes the entire reject circuit (reject loads R1 through R4 and their eight transmission
lines) invisible to the two amplifiers.
Figure
7-3
Gysel
Combiner
If an amplifier fails, its output becomes a virtual ground, as with the other combiners
studied. The impedance inverting properties of its two 1/4 wavelength output lines
present open circuits to the output load and its reject load. The improper (higher)
impedance presented to each good amplifier by the output circuit is brought back down
to 50 ohms by the reject loads and their network of 1/4 wavelength, 50 ohm
interconnecting transmission lines.