[SI-LIST] Re: Impedance Discontinuity @ SMA connector
- From: pwelling@xxxxxxxxxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 15 Jan 2002 16:39:27 -0700
Suresh,
Many times an "end launch" SMA works better. There is generally lower loss
(may not make a difference depending on operating frequency). It allows for
a better match with the center pin if you use a wide line Microstrip for the
center pin(if you provide containment by a can or other PWB features). If
you are using Stripline, locate the via to the inside trace as close as
possible to the end launch center pin pad as possible. There is already some
inductance in the center pin and the capacitance will look like a lumped
element. With higher frequencies the via will introduce loss. Be aware of
the planes that the via punches through, make sure the noise content isn't
too high with high sensitivity circuitry.
It is also good practice to use a solid plane for the ground pins of the SMA
connector. Whenever possible and when the operating frequency merits it, I
try to bury the pins - no thermal ties or wagon wheels to the planes.
Manufacturing may not allow you to bury the ground pin pads. You will also
want to reference the SMA ground pins to the Microstrip reference plane with
multiple vias depending on the operating frequency. Be aware again of
multiple closely spaced vias and their clearance holes. They may make
contiguous plane voids that create unplanned delays from longer return
currents having to go around the voids.
Philip Ross Wellington
Mgr. Signal Integrity & EMI
L-3 Communications CSW
-----Original Message-----
From: Suresh Sivasubramaniam [mailto:Suresh.Subramaniam@xxxxxxxxxx]
Sent: Tuesday, January 15, 2002 4:16 PM
To: Signal Integrity
Subject: [SI-LIST] Impedance Discontinuity @ SMA connector
Hello,
I think the question I am about to ask was raised or discussed earlier
(several months ago but could'nt find much in the archives). However, I
will ask it again. How can the impedance discontinuities caused by an
SMA connector be rectified?
In anticipation of edification
Thanks
Suresh
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