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I'm designing a low pass chebyshev filter using stepped impedance.

I'm using the book 'Microstrip Filters for RF/Microwave Applications' as a reference.

I have difficulty understanding how low and high impedances are defined. The book uses \$Z_{0L} = 93\,\Omega\$ and \$Z_{0C} = 24\,\Omega\$. I could not find an explanation for these values, I searched several articles but all uses an impedance between 20 and 120 Ω but does not explain how to calculate.

How can I get to this definition?

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  • \$\begingroup\$ If you're doing RF, "low" or "high" impedances are relative to 50\$\Omega\$. If you're doing video, 75\$\Omega\$. The "why" is partially traditional, and partially because that's what Just Works(TM). If you're doing digital logic, then 120\$\Omega\$, for the same reasons. \$\endgroup\$ – TimWescott Nov 15 '19 at 21:22
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I don't know that book, but chances are that \$Z_0\$ is simply the impedance of that piece of microstrip; it's pretty standard to use \$Z_0\$ as the symbol for reference impedance.

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