RE: [SI-LIST] : Antenna Problem on the Board

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From: Ron Miller (rmiller@brocade.com)
Date: Wed May 23 2001 - 10:08:42 PDT


Right angle bends have two effects:
 
1. the bend causes reflections because of the in LLLLLL _____LLLLLLL out
 
CCC
 
Gnd
 
model which in tranmission line terms is HIGH Z - LOW Z - HIGH Z
Causing reflections at each impedance change.
 
However for 5 mil wide traces these are very close together(~7 mils ~ 1
picosecond) and the reflections can be ignored up to at least 100 Mhz. So,
forget it for the
next few years.
 
2. The corner or bend also will effect the radiation pattern but simple
addition
of the radiation from one of the straight lines to the radiation from the
other straight section of the same line using trig can conceptually yield
the total radiation. How to figure the radiation from any straight line
however is a pretty tough job, and varies
with distance and especially is complex going from the near field to the far
field.
 
However, the bend or corner difference is trivial, compared to a straight
line and
can be ignored unless you are really intrested in the polarity of the
radiated wave
with respect to the board.
 
Bottom Line(for me in SI/EMI): Ignore it for next couple generations of
equipment.

Ron Miller
 

 
                                                                            

-----Original Message-----
From: Ken Cantrell [mailto:Ken.Cantrell@srccomp.com]
Sent: Wednesday, May 23, 2001 8:32 AM
To: Ken Cantrell; subramanya C K; Si-List
Subject: RE: [SI-LIST] : Antenna Problem on the Board

Subramanya,
I just read Scott McMorrow's prelimnary report that he is doing with Gus
Panella (Molex) on right angle vs radial vs chamfered bends. New data! How
exciting. I suggest you get a copy from Scott.
Ken
-----Original Message-----
From: Ken Cantrell [mailto:Ken.Cantrell@srccomp.com]
Sent: Wednesday, May 23, 2001 8:25 AM
To: subramanya C K; Si-List
Subject: RE: [SI-LIST] : Antenna Problem on the Board

Subramanya,
You just missed a long running discussion on the subject. Look for any of
the list items under "MECL System Design Handbook". Cutting to the chase,
it shouldn't have any measureable effect on your system unless you are at 50
GHz or above.
Ken
-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of subramanya C K
Sent: Tuesday, May 22, 2001 11:51 PM
To: Si-List
Subject: [SI-LIST] : Antenna Problem on the Board

Hello SI Gurus,
I have a basic question here. We all know that "Right angled traces are
never used on PCBs" as the act as antennas (better antennas than the curved
traces). In an article I read that this radiation is due not to the
frequency of the signal , but to it's rise time. Could someone please
explain me this theory ?
 
 
Thanks and Regards,
Subramanya C K

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