RF Electronics Chapter 3: Transformers and Hybrids Page 60
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 3.16 shows the corresponding frequency response. It can be seen that a good
isolation and return loss on all ports is obtained at the design frequency of 1 MHz.
Constructing this hybrid normally results in a close agreement with the simulation and
typically result in a three decade frequency bandwidth.
Figure 3.16. Simulated performance of Wilkinson Hybrid.
The 25 Ω to 50 Ω impedance transformation requires a 2 = 1.414 turns ratio. A 2 to 3
turns ratio is the nearest. For a 25 Ω impedance on the 2x7 turn winding the 3x7 turn
winding corresponds to a 56.25 Ω impedance. Tuning the Port 1 impedance to 65.25 Ω
results in a better isolation. In addition, the return loss from all ports can be improved by
tuning a capacitor at the junction of the two transformers, to partially cancel the leakage
and magnetising inductances at some frequencies. That also increases the bandwidth.
Figure 3.17 shows the resulting performance.
Figure 3.17. Performance of the optimised Wilkinson Hybrid.
RF Electronics: Design and Simulation
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