RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 90
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 4.41. /4 20 dB coupler schematic and corresponding Microstrip layout.
Figure 4.42. /4 20 dB coupler schematic and corresponding Microstrip layout.
Figure 4.43. /4 Microstrip 20 dB coupler performance.
Having a different electrical length for even and odd mode impedances makes it difficult
to set the line length to correspond to 90. The coupling line length and gap can be
obtained without using the transmission line calculator of figure 4.40. The coupler line
length can be tuned to maximise the output at 900 MHz, while observing figure 4.43.
That should result in a coupling null at close to twice the frequency for maximum
coupling, (1.8 GHz for figure 4.43). The line spacing can be tuned to give the -20.11 dB
attenuation, to produce the coupled output 20 dB below the direct output by tuning those.
The line width can be tuned to give a low S11 return loss up to about 1.2 GHz. Double
clicking on the MCLIN element after tuning shows the values in figure 4.41. Since there
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