RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 75
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
and 60 respectively, similar to the values of the compensated Wilkinson hybrid shown
in figure 4.12. The initial value for Z4 is chosen to be 50 as that should be a close match
to the impedance at port 1 and Z3 is chosen to be 55 , being in between the values of
Z2 and Z4. The initial value of R1 is chosen to be 100 , being the value of the isolating
resistor in figure 4.12. R2 is chosen to be 200 , similar to R2 in figure 4.14 and R3 is
chosen as 400 . The initial value of F0 is chosen to be 156 MHz, the geometric mean of
90 MHz and 270 MHz. The optimisation goals are set up to match the specifications. To
achieve a better return loss and isolation, the goals are for S
11
< -32 dB, S
22
< -32 dB and
S
32
< -33 dB. Setting the circuit to optimise using the Simplex optimiser then yields the
circuit values shown in figure 4.16. This circuit achieves the specifications as shown in
figure 4.17. Notice that no optimisation goals are set for the through coupling, S
21
, since
if the circuit is matched then the coupling loss will be as small as possible.
Figure 4.16. Circuit for a 90 MHz to 270 MHz Wilkinson hybrid.
Figure 4.17. Simulated performance of the hybrid of figure 4.16.
RF Electronics: Design and Simulation
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