EMRFD Message Archive 8486

Message Date From Subject
8486 2013-04-08 18:37:22 Jerry Haigwood 50 ohm stripline
Hi All,

I have a question about a 50 ohm stripline. I have some 0.062 thick
FR-4 copper clad. How wide would the trace have to be in order to equal 50
ohms? Is there basic formula that I could use?

Jerry W5JH

"building something without experimenting is just solder practice"





[Non-text portions of this message have been removed]
8487 2013-04-08 18:41:30 Jerry Haigwood Re: 50 ohm stripline
Of course the copper clad is double sided..



8488 2013-04-08 18:52:05 Kerry Re: 50 ohm stripline
There are quite a few on-line calculators such as;

http://www.microwaves101.com/encyclopedia/calmstrip.cfm

FR-4 varies a little in permittivity, both intrinsically and with frequency, which is one reason it's not usually used over about 1 GHz.

Permittivity of 4.5 is about average; the line width for Zo 50 ohms in microstrip on 0.062" substrate is about 0.1".

Kerry VK2TIL.
8489 2013-04-08 18:58:32 Dave Re: 50 ohm stripline
Jerry:
Several calculators exist on the net. I usually use .100" for 50
ohms. According to the KICAD stripline calculator, 50 ohms is .115 inch
and .100" is 54 ohms.

Dave - WB6DHW
<http://wb6dhw.com>

8490 2013-04-08 19:08:48 dixonglennb Re: 50 ohm stripline
Microstrip, by the way, is the trace on one side and ground plane on the other. This would be what the others are referring to...about 0.1". Stripline is an internal signal trace with a ground plane above and below...probably not what you really meant. You can also do a signal trace with copper on the opposite side and copper fill on the top. This would need a thinner signal trace, and you must connect the ground on either side of the signal trace to the bottom copper at regular intervals near the edge facing the signal trace. Sort of like the eyelets in a boot with a skinny tongue being the signal trace. I like that structure a lot because not as many flux lines go through the FR4 material so there is lower loss, but this structure is not in the calculators that I'm aware of.

73,
Glenn AC7ZN
8491 2013-04-08 19:13:22 Kerry Re: 50 ohm stripline
Glenn; are you referring to co-planar waveguide (CPW)?

If so, there are on-line calculators;

http://www.microwaves101.com/encyclopedia/calcpw.cfm

CPW isn't so forgiving of dimensional errors as is stripline/embedded microstrip.

Trivia of the day; the abbreviation CPW is also the initials of its inventor.

Kerry VK2TIL.
8492 2013-04-08 19:44:44 Jerry Haigwood Re: 50 ohm stripline
Sorry to ask for the wrong thing. But, I am glad you guys figured out what
I really was asking.

Jerry W5JH

"building something without experimenting is just solder practice"







8493 2013-04-08 21:39:44 Graham / KE9H Re: 50 ohm stripline
Jerry:

Stripline usually refers to buried conductors inside the PCB.

I think you are asking about microstrip conductors, which is
an exposed conductor on one side, and the other side a solid groundplane.

For 62 mil thick FR-4 (Er = approx. 4.8), a 50 Ohm microstrip calculates
to be about 110 mils wide.
Measuring the impedance on implemented boards, I find something closer
to 100 mils wide works better. So something in the range of 100 to 110
mils
wide will work fine. The gap to anything nearby needs to be at least
one half
the width of the line on each side.


I usually use a microstrip calculator, such as:

http://www.eeweb.com/toolbox/microstrip-impedance

The equations are conveniently located lower in the article. :-)

Or just Google "Microstrip calculator."

--- Graham / KE9H

==

8494 2013-04-08 21:57:19 victor Re: 50 ohm stripline
THE free ultimate PCB transmission line calculator you really need is Tx-line from AWR:
http://www.awrcorp.com/products/optional-products/tx-line-transmission-line-calculator
And the specific transmission line that you would be using is "CPW ground" which is a microstrip line with ground at both sides of the transmission line. You need to use wide enough distance from the transmission line to the co-plane ground so the main influence
8495 2013-04-08 23:50:01 Kerry Re: 50 ohm stripline
Thanks for that, Victor.

I should add that my earlier post should have read "... microstrip/embedded
stripline ...".

I wrote it back-to-front; perhaps I can add dyslexia to my other ills. :)

Kerry.
8497 2013-04-09 06:14:08 Chris Trask Re: 50 ohm stripline
>
> I have a question about a 50 ohm stripline. I have some 0.062 thick
>FR-4 copper clad. How wide would the trace have to be in order to equal 50
>ohms? Is there basic formula that I could use?
>

Without getting into the fine details of copper thickness, 0.080" will be pretty close.


Chris
8498 2013-04-09 21:41:44 Ashhar Farhan Re: 50 ohm stripline
One could just lay an insulated wire along a ground plane. There are
standard formulae in any microwave handbook for this kind of a
transmission line. Just be sure to use a wire with insulation that has
low loss as a dielectric at the operating frequencies.

- farhan

On 4/9/13, Chris Trask <christrask@earthlink.net> wrote:
>>
>> I have a question about a 50 ohm stripline. I have some 0.062 thick
>>FR-4 copper clad. How wide would the trace have to be in order to equal
>> 50
>>ohms? Is there basic formula that I could use?
>>
>
> Without getting into the fine details of copper thickness, 0.080" will
> be pretty close.
>
>
> Chris
>

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