OBG Home - how to confirm the impedance of the microstrip?

mckinson

Joined: 03 Sep 2003
Posts: 136

28 Nov 2004 15:24 Hello ,about the 50 ohms microstrip !

Hello ,guys . Anybody knows how to confirm the impedance of the microstrip ?
For example ,I have simulated the width of the microstrip for 50 homs .But I don't
know whether the impedance of pcb tracks from pcb manufactory is correct ? How to confirm ? Best regards !

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BigBoss

Joined: 17 Nov 2001
Posts: 1177
Helped: 89
Location: Earth

28 Nov 2004 18:38 Re: Hello ,about the 50 ohms microstrip !

mckinson wrote:

Connect an 50 Ohm low ESR and inductance resistor (or 2 parallel 100 Ohm) at the end of line and measure with VNA.

vfone

Joined: 10 Oct 2001
Posts: 2578
Helped: 358

28 Nov 2004 22:45 Re: Hello ,about the 50 ohms microstrip !

You don’t need any extra components. Just measure with Network Analyzer, that is connected at both ends of the line.

sergio mariotti

Joined: 22 Dec 2003
Posts: 469
Helped: 43
Location: Italy

29 Nov 2004 0:03 Re: Hello ,about the 50 ohms microstrip !

vfone wrote:

You dont need any extra components. Just measure with Network Analyzer, that is connected at both ends of the line.

Yes, correct, but usually it may be experimented that measured Zo differ a lot from the simulated one, also in the case that all is correct and well manufactured.
This is due to end effects and ľstrip launchers.
To reduce this effect and focalize the attention to the line only, use a Time Domain VNA. Both Agilent and Anritsu have very efficent and useful TD algoritms.

mckinson

Joined: 03 Sep 2003
Posts: 136

29 Nov 2004 16:14 Hello ,about the 50 ohms microstrip !

Appreciated !Do you think that is accurate measure the character impedance Z0 by the VNA ?
Could you please tell me the detail stap for measurement ? Best regards !

vfone

Joined: 10 Oct 2001
Posts: 2578
Helped: 358

29 Nov 2004 17:59 Re: Hello ,about the 50 ohms microstrip !

By definition the main designation of VNA is to measure impedances.
Time Domain Reflectometry (TDR) is more accurate than frequency domain Vector Network Analysis (VNA), because do not depend by frequency.
But for commercial applications frequency domain is more than ok.
Check this document:
http://cp.literature.agilent.com/litweb/pdf/5968-1947E.pdf

hitmo

Joined: 04 Jan 2005
Posts: 40

13 Jan 2005 18:55 Re: Hello ,about the 50 ohms microstrip !

u can also do it with network ana. just measure inserstion loss and return loss on smith chart. return loss will tell u the impedance of the line. if the rerunloss is as close as possible to center of the smith chart its a 50ohm line

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