RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 95
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
structure has no radiation losses. The disadvantage is that a non-planar structure is
required.
TXLine is not capable of calculation the broadside-coupled transmission-line coupling
gap (s) and line width (W), shown in figure 4.49. Books like Matthei, Young and Jones
[11]. Microwave Filters, Impedance Matching Networks and Coupling Structures. Artech
House 1980. (McGraw Hill 1964) pages 180 and 181 give empirical equations for Z
oo
and
Z
oe
are given in equations 4.23 and 4.24. The capacitance C
fe
and C
fo
are fringing
capacitances between the coupled lines and the ground plane and these can be determined
from figure 4.50.
Figure 4.50. Values for C
fe
and C
fo
from Matthei, Young and Jones, pp181.
��
�
�����
√
�
�
⁄
� � ⁄
���� � ⁄ �
�
�
��
�
Eqn. 4.23
��
�
�����
√
�
�
⁄
� � ⁄
���� � ⁄ �
�
�
�
�
�
��
�
Eqn. 4.24
Using the two-line broadside coupled line element, SBCPL, and the schematic circuit
simulation, allows an easier and more accurate determination of the broadside coupler
parameters, than using equations 4.23, 4.24 and figure 4.50. The SBCPL element is a
two-line broadside-coupled line element. The cross-section is similar to that of
figure 4.49.
In addition, the width of each of the lines can be specified independently, the lines can be
offset and the dielectric constants between the lines can be different from that above and
below the line. None of these advanced features can be determined using the alternative
techniques. The use of the SBCPL element to determine the required coupling gap and
line width for a coupler is illustrated in the following example.
RF Electronics: Design and Simulation
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