RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 72
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Compensated Wilkinson Hybrid
Figure 4.12. Compensated Wilkinson hybrid.
In a compensated Wilkinson hybrid, a two-step impedance transformation is used, like
the two line impedance transformation of figures 4.1 and 4.2. The resulting circuit is
shown in figure 4.12. The impedance transformation from line TL3 is from 50 at port
1 to 35.36 at the right of TL3. Lines TL1 and TL2 do an impedance transformation
from 50 at port 2 and port 3 to 70.71 at the left hand side of transmission lines TL1
and TL2. Those in parallel give a 35.36 , which matches that at the right hand side of
line TL3. Each of the three transmission lines will thus have the same impedance
transformation ratio of 2.
Figure 4.13 shows a comparison between the conventional (red), and the compensated
(blue) Wilkinson hybrid. The compensated Wilkinson hybrid has a wider frequency
response for both the isolation and coupling. In addition, the compensated Wilkinson
hybrid uses lower impedance transmission lines, resulting in wider track widths for the
Microstrip layout, thus lowering the resistive losses in the circuit.
Figure 4.13. Comparison of conventional and compensated Wilkinson hybrid performance.
RES
ID=R1
R=100 Ohm
TLIN
ID=TL1
Z0=59.46 Ohm
EL=90 Deg
F0=1000 MHz
TLIN
ID=TL2
Z0=59.46 Ohm
EL=90 Deg
F0=1000 MHz
TLIN
ID=TL3
Z0=42.05 Ohm
EL=90 Deg
F0=1000 MHz
PORT
P=1
Z=50 Ohm
PORT
P=2
Z=50 Ohm
PORT
P=3
Z=50 Ohm
RF Electronics: Design and Simulation
72 www.cadence.com/go/awr
