PCB trace 50 ohm impedence

Community PCB Design
1

Hello

I am trying to create a PCB trace line from a GPS receiver to a GPS patch antenna. This antenna operates at 1.5GHz and needs a 50 ohm impedance line.

I was told that copper at 1Ghz has a Dielectric Constant of roughly 3.5.

using

http://www.pcb123.com/help/calculators/microstrip.html

and

er: 3.5

H: 3 mil

T: 1.4 mil

Zo: 50 ohm

I see a PCB trace needed of 4.5 mil

Does this make sense? Is the dielectric constant of copper at 1.5ghz different than 1ghz? I am unable to find this info.

Thanks

Lucas

2

It isn’t all that critical. I often just use a 0.1" wide track over a copper ground on the other side of the board (1.6 mm thick) for microstrip, which gives about 50 ohms with an e of 4.35. I just checked with the Pulsonix design calculator, and got 0.117".

It’s the fibreglass dielectric constant that is important, not that of the copper. You need special material like Duroid if you want exact parameters at different frequencies, they just aren’t available for FR4. Ask your board supplier for the spec. of the material they use if you want to be sure.

Leon

3

.1", you use a 100mil trace?

4

Yes. It should be a bit more, as I said.

Leon

5

thanks

6

Hi, I know it’s an old thread, but I think it could be still usefull for someone…

I need to make a 50 ohm impedance pcb track, so I found online calculator:

http://www.technick.net/public/code/cp_ … microstrip

I’m using FR4 double sided PCB (er=3.7 @ 1MHz, 3.8@1GHz, values from productor datasheet).

I have to make a PCB track with impedance of about 70 ohm, so I have to use the values of:

relative permeability (er) = 3,7-3,8 (from datasheet)

width of track = 1,65 mm

trace thickness = 0,2 mm (from pcb datasheet)

height of dielectric above return plane = 1,6 mm (from datasheet)

I obtain a Z0 of 70,8 ohm.

Now, I could find right track length using Smith chart, or modify the values to obtain 50 ohm value.

7

The track length won’t have any effect on the impedance.

8

Sorry, I lost some lines: I mean I can change length using multiple of lengthwave quarters to achieve useful length: Length=(2k+1)*wavelength/4.

9

El Berto:
Hi, I know it’s an old thread, but I think it could be still usefull for someone…

I need to make a 50 ohm impedance pcb track, so I found online calculator:

http://www.technick.net/public/code/cp_ … microstrip

I’m using FR4 double sided PCB (er=3.7 @ 1MHz, 3.8@1GHz, values from productor datasheet).

I have to make a PCB track with impedance of about 70 ohm, so I have to use the values of:

relative permeability (er) = 3,7-3,8 (from datasheet)

width of track = 1,65 mm

trace thickness = 0,2 mm (from pcb datasheet)

height of dielectric above return plane = 1,6 mm (from datasheet)

I obtain a Z0 of 70,8 ohm.

Now, I could find right track length using Smith chart, or modify the values to obtain 50 ohm value.

0.2mm copper thickness? that is very very thick. standard is 1oz/2oz , ~35um / ~70um

10

langwadt:
0.2mm copper thickness? that is very very thick. standard is 1oz/2oz , ~35um / ~70um

It’s an old board, I don’t remember for what it has been bought, maybe is a non-standard board for particular use…