# Microstrip Length

Discussion in 'Electronic Design' started by Philip Newman, Apr 8, 2004.

1. ### Philip NewmanGuest

How can I calculate the length of a line of microstrip, by using the
Effective Electrical Length and it's impedance?

I know how to calculate the width of the line, but what about the length?

I can use ADS' LineCalc to achieve this, but I wish to find a formula. What
formula does LineCalc use? I cannot find it anywhere.

Assume I know all the substrate and metallisation parameters.

Cheers

Phil

2. ### Active8Guest

Use the VP factor, 1/sqrt(e_r) where e_r is the dielectric constant
of the substrate.

l_phys = VP * l_elec

3. ### Philip NewmanGuest

Hmm, doesn't work for my values or consistent with LineCalc. I think I may
be confusing Electrical Length with Phase Change.

I looked in my Pozar Book, and found the equations. They work out fine, so
no panick!

Cheers anyway

Phil

4. ### John LarkinGuest

Appcad reports this, based on effective dielectric constant Eef; it
gives you Eef, too.

John

5. ### MacGuest

This doesn't work for microstrip. The deal with microstrip is that the
effective dielectric constant is somewhere in between that of the
dielectric medium and that of free-space (or other surrounding medium).
This sort of makes sense if you think in terms of the field lines
emmanating from the microstrip: some of them go through air (or other
surrounding medium) and some of them go through the substrate.

Pozar's book (I have _Microwave Engineering_ second edition) gives
equations, as the OP already discovered.

Mac
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6. ### danesh.8

1
0
Jan 27, 2009
Hi Mac,

can u share the formula that you found from pozar. chapter or the book page