RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 103
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Lin [20] used a 7 track Lange coupler for a Marchand Balun operating at 21-41 GHz and
shown in figure 4.65. The chip size is approximately 200 µm x 420 µm.
Figure 4.65 Chip photograph of 21-41 GHz MMIC Marchand Balun [20].
By isolating the ground-plane layer under the coupled lines, Zhang [21] was able to
increase the even mode impedance of the coupling lines, to obtain a Marchand Balun
using Microstrip coupled lines. For such a circuit, care needs to be taken with the coupling
between the isolated ground-plane layer tracks and the ground of the mounting structure.
Stripline techniques can be used to obtain a practical Marchand Balun by putting coupled
tracks on both sides of a 0.2033mm thick RO4003 [5] substrate and make this into a 3
layer SSUBT substrate by mounting single sided 1.525mm substrates on both sides, using
Prepreg sheets [12], as described in chapter 11 under heading Multilayer Boards. Figure
4.66 shows the resulting schematic diagram. Since the impedance of the right stub (Zstub)
in figure 4.58, is different from Z0 of the left input coupling line, the widths of the
coupling lines is W1 for the input and W2 for the stub coupling structures. In addition,
the amount of coupling can be varied by varying the offset between the coupling lines. It
can be seen that after optimisation, there is little difference between TL1 and TL2 of
figure 4.66
Figure 4.66 Stripline Marchand Balun Circuit.
RF Electronics: Design and Simulation
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