Phil et al. -
On Thu, Jan 05, 2006 at 04:17:44PM -0500, Phil Taylor wrote:
>
> 50 ohm hard coax makes sharp bends all the time, but it's still 50 ohm.
> Reflections do exist but they're way down. This is no doubt because the parts
> are designed very carefully.
Right. Someone tuned the excess inductance and excess capacitance
of the non-coaxial feature to match, so the asyptotic low frequency
response is unchanged. That's what proper beveling of the corners
of a right angle PC board trace (a.k.a. waveguide) does.
When you get down to wavelengths that are similar to the device size,
this simple tuning isn't enough, and you need 3-D calculation of
S-parameters (or years of experience, or both) to guide the design.
> Isn't tuning trace _lengths_ more important on pcbs than what types of corners
> you're using?
Depends, but usually yes.
> Or another way to consider this: Isn't it possible to make a trace that a
> certain frequency cannot pass through due to nothing other than its length?
If the trace is straight (or at least nearly constant impedance)
and the end is terminated correctly, no.
- Larry
Attachment:
signature.asc
Description: Digital signature