Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Traces of.....PCBs


Forget the impedance matching, there are radiative 
losses associated with the microstrip gemoetry (copper 
trace over ground plane) most PCB designers are using 
which do limit the usable distances to a few inches 
at these frequencies.

One improvement is to use buried stripline.  In this
transmission line geometry, the radiative losses are 
greatly reduced.  The ground plane-copper trace-ground
plane construction confines the fields in a much smaller
cross section.  However, 4-5 inches in FR-4 is still a 
very long distance even at 3.125 X 0.7 = 2.2Ghz.

Best Regards,

Pat Gilliland


How long of traces are you getting on FR-4? Have you actually fabricated

Our network analyzer tests indicate that FR-4 dies horribly (lossy) above
about 1.5 Gb/s. By the time we get to 3 GHz all the analyzer is displaying
is the analyzer receiver input noise, looking in vain for signals......

Your Tricks & Tips look like they would help, but I would be very
interested in hearing from anyone who claims to have successfully used FR-4
in 5+ GHz circuits over more than 3-4 inches and, if so, what kind of signals.


Larry Miller