Re: [SI-LIST] : SMA connector routing

Ray Anderson (raymonda@radium.eng.sun.com)
Thu, 18 Feb 1999 10:58:19 -0800 (PST)

It's been quite while since I've thought about this, but if
I remember correctly, when I used to work with 14GHz
satcom stuff we would on occassion "neck-down" the transmission
line going to a through hole connector. By raising the impedance
of the transmission line for a "short" distance just before it hit
the connector it would look slightly inductive and would partially
compensate for the lumped capacitive load the through hole center pin
via would provide and tune-out the discontinuity somewhat.

Don't have any specific quantitative info, but you might try some
what-if scenarios with spice to see if you can come up with an
acceptable solution.

You might also consider increasing the size of the anti-via clearance
around the center-pin pad to reduce the capacitance to ground. Also,
if you are going through a multilayer board, if possible, make sure your
center pin isn't connected to floating "do nothing" pads in the inner layers.
(this makes the fab people nervous though:)

-Ray Anderson
Sun Microsystems Inc.

> From: "Ellis, John R" <EllisJR@bergelect.com>
> To: "'si-list@silab.Eng.Sun.COM'" <si-list@silab.eng.sun.com>
> Subject: [SI-LIST] : SMA connector routing
> Date: Thu, 18 Feb 1999 11:53:11 -0600
>
> Whenever we route to a through hole SMA connector we get abig capacitive dip
> in the via beneath the connector itself. Does anyone have any board layout
> recommendations to reduce this dip? I'm using end launch connectors
> whenever I can, but there are times when only the the thru-hole will
> suffice.
>
> John Ellis
> FCI
>
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