RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 78
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
often ignored in practice. Due to this frequency dependence of the losses, it is better to
optimise for input reflection coefficient rather than transfer function since a low input
reflection coefficient ensures all the energy passes through the hybrid, thus giving the
highest S
21
possible. Optimising for a value of S
21
may result in a poor return loss at lower
frequencies.
Quarter Wave Hybrid or 1.5 Rat-Race Hybrid
Figure 4.21. 1.5 Rat-Race hybrid.
Figure 4.22. Performance of 1.5 Rat-Race hybrid.
The circuit diagram of this hybrid is shown in figure 4.21 and its performance is shown
in figure 4.22. For the analysis, consider the function of the hybrid. If an input is applied
to port 1, then no signal should appear at port 3, resulting at 0 Volt at port 3. Under these
conditions, the circuit is similar to the Wilkinson hybrid of figures 4.6 and 4.7 and in
figure 4.21, no current flows into TL4 of at port 2 and into TL3 at port 4. The transmission
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
TLIN
ID=TL3
Z0=70.7 Ohm
EL=270 Deg
F0=1000 MHz
TLIN
ID=TL4
Z0=70.7 Ohm
EL=90 Deg
F0=1000 MHz
PORT
P=1
Z=50 Ohm
PORT
P=3
Z=50 Ohm
PORT
P=2
Z=50 Ohm
PORT
P=4
Z=50 Ohm
RF Electronics: Design and Simulation
78 www.cadence.com/go/awr
