RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 94
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 4.48. Lange coupler layout from MLANGE and schematic.
Even having these parallel lines result in very fine track widths and coupling gaps, making
the Lange Coupler expensive to make. The Lange coupler [10] is however, the only planar
hybrid that offers better than an octave (2:1) of useable bandwidth. With the high cost of
manufacturing the Lange Coupler, due to the small track and gap widths and the high cost
of attaching the bond wires, Lange Couplers are not often used. The required coupling
can be obtained at a lower cost and can be better controlled, using broadside coupled lines
and multilayer RF printed Circuit Boards. They can also be implemented using Low
Temperature Co-fired Ceramic (LTCC) substrates, which are discussed in chapter 11.
Since CADENCE AWR DE V10, the Lange coupler circuit element MLANGE and the
associated layout as shown in the left of figure 4.48 is no longer available since it was not
accurate enough. The replacement circuit elements MLANG and the more accurate
M2LANGE, which includes an EM model, only shows the thin coupled lines of the
schematic in the layout.
Broadside Coupled Lines
It is possible to have multilayer printed circuit boards with RF substrates. These can be
used to design coupling structures with higher coupling and 3 dB couplers are quite
practical. The typical configuration is shown in figure 4.49.
Figure 4.49. Stripline broadside coupled lines
The advantages of this structure are firstly that bigger coupling between the transmission-
lines can be obtained with a good control over impedance values. Secondly, the Stripline
1
2 3
4
MLANGE
ID=TL1
N=4
W=1 mm
S=1 mm
L=10 mm
RF Electronics: Design and Simulation
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