RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 67
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
bandwidth wider. This then allows very wide bandwidth impedance transformers, with
tightly specified VSWR's to be designed.
Wilkinson Transmission Line Hybrid
The Wilkinson transmission line hybrid [4] consists of two quarter-wavelength long
transmission lines forming a combiner, together with a load resistor to provide isolation.
The circuit is shown in figure 4.4 and the performance is shown in figure 4.5.
Figure 4.4. Ideal Wilkinson hybrid.
For the analysis, an input is applied to port 2 in figure 4.4. For proper hybrid operation,
no voltage should appear at Port 3. Transmission line TL2 has a standing wave on it with
0 Volt at the Port 3 side. Since the line is one-quarter wave long, there will be no current
flowing into the line at the Port 1 side, as shown in figure 4.6. For the analysis of the
voltage on port 1, we can thus remove TL2, since it is an open circuit at the port 1 end.
The voltage at port 1 will thus simply be what we would have if one had the transmission
line only, as shown in figure 4.7.
Figure 4.5. Ideal Wilkinson hybrid.
TLIN
ID=TL1
Z0=70.7 Ohm
EL=90 Deg
F0=1000 MHz
TLIN
ID=TL2
Z0=70.7 Ohm
EL=90 Deg
F0=1000 MHz
RES
ID=R1
R=100 Ohm
PORT
P=1
Z=50 Ohm
PORT
P=2
Z=50 Ohm
PORT
P=3
Z=50 Ohm
Vc
Va
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