If you want to take the guesswork out of microwave (or in general above
Gigahertz ) circuits, download Sonnet Lite (free license tied to machine
hard drive)  or Microwave Office (30day trial) . They both do 3d EM
simulations using a method of moments (finite element analisys ) of planar
structures such as microstrips, striplines, circuit traces, vias etc up to
the 100 GHz range with accurate results since they compute current flow
distributions rather than rely on approximate models.

Best Regards,
Matt Tudor, MSEE- RF Design & Consulting
Gigahertz Electronics
http://www.gigahertzelectronics.com

-----Original Message-----
From: Mike Reagan <[EMAIL PROTECTED]>
To: Protel EDA Forum <[EMAIL PROTECTED]>
Date: Tuesday, November 27, 2001 4:35 PM
Subject: Re: [PEDA] Vias & trace length


>Sean.
>Cant say that I have ever attempted to pass 2.5 Ghz thru a via.  We design
>our boards so the "high speed" stuff never passes  thru vias.  If you need
>to use them for High Speed then I would recommend using blind and buried
>vias since they inhibit much  less capacitive and inductive properties.
>Unfortunately,  the effects of the vias has been mainly guess work by RF
>engineers. ( I know I am going to receive some heat for this)     I
>recommend reading the article that Doug Brooks wrote ( I said Bill Brooks
>before) about the effects  of vias on transmission lines. His data was
>measured from actual board designs using a TDR.  But his measurements were
>not at 2.5 Ghz.
>
>Mike Reagan
>EDSI Frederick MD
>
>
>
>----- Original Message -----
>From: Sean James <[EMAIL PROTECTED]>
>To: Protel EDA Forum <[EMAIL PROTECTED]>
>Sent: Tuesday, November 27, 2001 2:41 PM
>Subject: Re: [PEDA] Vias & trace length
>
>
>> My design is 2.5Ghz, so via length is critical.
>> Sean James
>> PCB Designer
>> Telecast Fiber Systems, Inc.
>> 102 Grove Street
>> Worcester, MA 01605
>> (TEL) 508.754.4858 x33
>> (FAX) 413.541.6170
>> ----- Original Message -----
>> From: "Mike Reagan" <[EMAIL PROTECTED]>
>> To: "Protel EDA Forum" <[EMAIL PROTECTED]>
>> Sent: Tuesday, November 27, 2001 12:39 PM
>> Subject: Re: [PEDA] Vias & trace length
>>
>>
>> >
>> >
>> >
>> > Is there any way to get Protel to add vias to an overall trace length?
>Ex.
>> A
>> > via going from top to bottom thru an .062" board would add .062" to a
>> total
>> > trace length (PCAD/ACCEL does this).
>> >
>> > Sean,
>> > I don't think .062 inch for any digital signal under 500 mhz makes any
>> > difference.  The actual capacitance of the via will pose more of a
>problem
>> > than the trace length.   Actual measurements made by Bill Brooks
>> > www.ultracad.com  and contributing editor to PCD magazine shows no
>> relevant
>> > impedance changes with vias placed in a trace.  There are little
>hic-cups
>> in
>> > the impedance but it really doesn't change much.   I wish protel would
>> give
>> > me a calculation of the capacitance with the via included.   A trace
>> length
>> > is irrelevant unless it approaches a critical length for the signal,
but
>> > loss can become a  bigger factor.
>> > Question;   Why don't you use Acell PCAD?    personally I think it
sucks
>> >
>> >
>> > Mike Reagan
>> > EDSI
>> > Frederick MD
>> >
>>


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