RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 85
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
split at TL6 results in a slightly smaller output at port 3, due to resistive losses in TL3,
TL14, TL18, TL20 and TL7. A slight fine-tuning is included by making the line-width of
W50F = W50 +D50F, where D50F is a small correction factor. D50F is then tuned to
change the power split to allow for these losses and make the outputs at ports 2 and 3
identical at the centre frequency.
Figure 4.33. Folded Microstrip Branchline coupler PCB layout.
This changes power split causes a change in the impedance seen at terminal 1 of TL6 and
will require a slight change in the impedance transformation produced by TL1 and TL4,
to present a 50 impedance (S
11
) at port 1. This is achieved by making W35F = W35 +
D35F, where D35F is a small correction factor. D35F is tuned to make S
11
as small as
possible at the centre frequency.
Figure 4.34 shows the frequency response of the resulting folded Branchline coupler.
There is virtually no difference between figure 4.31 and 4.34. However, the circuit with
the bent lines occupies a much smaller area. Constructing the hybrid of figure 4.33 results
in a measured performance, that is very close to the calculated performance shown in
figure 4.34.
Figure 4.34. Folded Microstrip Branchline coupler amplitude response.
RF Electronics: Design and Simulation
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