RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 97
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Entering these values in the SBCPL element and then fine-tuning the track width, track
length and offset, allows the required performance to be obtained. Polyethylene has a
dielectric constant of
r
= 2.26 and Perspex has a dielectric constant of 3.42 ±0.3.
Figure 4.52. MWO broadside coupled-line circuit using SBCPL.
Figure 4.53. Performance of broadside coupled-line circuit using SBCPL element.
Tuning the coupler length (L = 449) sets the centre frequency of the coupler to 100 MHz
and tuning the line width (W = 12.2) adjusts the coupling to have close to 3 dB coupling
over the 85 MHz to 115 MHz frequency range and achieve a return loss on the ports of
less than -20 dB. The resulting MWO circuit diagram is shown in figure 4.52 and its
performance is shown in figure 4.53. The track width of 12.2 mm and length of 440 mm
obtained from MWO agrees closely with the 12.7 mm and 500 mm obtained for the earlier
design, which used equations 4.23 and 4.24 together with figure 4.50. The MWO design
is far more accurate since it allows for losses in the dielectric and the Perspex sheet for
separating the tracks, having a different dielectric constant and loss tangents compared
with the Polyethylene. The constructed coupler has a measured isolation and coupling
RF Electronics: Design and Simulation
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