Subject: Terminate/launch microstrip??
Date: Fri, 29 Nov 2002 04:51:23 -0800
X-Mailer: Mozilla 4.78 [en] (Win98; U)
I've been trying (unsuccessfully) to get signals
of 50 ohm microstrip transmission lines on .062"
For terminations, I've been trying two 100 ohm or
50 ohm 1206 SMT resistors in various mechanical
configurations. The only thing that seems to work
to hang one 50 ohm resistor off the end of the
normal to the board. I soldered it to the trace
top and built up the groundplane on the backside
to meet the end of the resistor.
Works, but ain't rugged at all.
This is a directional probe, so will be exposed to
(un)nimble fingers in use.
Is there some black magic I can apply to get the
to properly terminate when placed on top of the
Smaller resistors would probably help, but 1206 is
what I got.
The other problem is launching into the
I need the input to be normal to the board. The
I've come up with so far is to drill mostly thru
backside and stuff .095 rigid coax thru the hole
and solder to the trace. The TDR shows a nasty
reflection about 50pS wide of 3% or so. By
how far I shove the coax into the board I can
the dip to a ring, but can't make it smaller.
doesn't sound like much, but it's 10% of the
length of the
More black magic??
A long time ago, I read an article about diddling
trace geometry to compensate for launcher
but can't find it. I'm only going to build one,
I thought about trying to spice model it, but it's
related to geometry than to parasitics in the
themselves, yes? no? I'm coming to the conclusion
there is no way I can get a resistor on the top to
have a low inductance connection to the
There's gotta be a way. RF guys do it every day??
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