Distance Between Line and Ground ???

[cmkrkmz]

hello everyone,
does anybody knows that what is the design rule about the distance between a microstrip line and the ground area in the same layer? i think it is about the RF power in that line and also frequency, but i couln't find the information. how far should i place the polygon from the line that carries high RF power in order to get good EM results ?
thanks

 

[jiripolivka]

In any coaxial, microstrip or generally TEM line, line impedance is the primary parameter. The impedance of a microstrip line is a function of its width and "distance to ground" depending also on substrate permittivity.
In any handbook or textbook on microstrip lines, you can find a simple diagram used to design line width in a particular substrate.

If you intend to apply a high RF or DC voltage so the substrate dielectric is stressed, you should design it on the base of substrate dielectric thickness, then determine line width for a desired line impedance.

 

[cmkrkmz]

thank you for reply jiripolivka.
i think the line width and thickness is about line impedance. i have no problem here. what i wanna know is that;
i will apply to the line high RF power and worry about the distance between the line and ground plane in the top layer. i heard that "if the distance between the ground and line is 5-6 times of the dielectric thickness, that's OK" but i am not sure ???
thanks

 

[volker_muehlhaus]

i think the line width and thickness is about line impedance.

Wrong. For a microstrip line, the signal is between the line and the ground below, and the line impedance is set by the line width and the distance to the ground below.

Microstrip Line Calculator | em: talk

---------- Post added at 08:51 ---------- Previous post was at 08:47 ----------

about the distance between a microstrip line and the ground area in the same layer?

OK, we all might have misunderstood your initial question. You ask about the distance between a microstrip conductor and some other (grounded) metal on the same layer?

 

[jiripolivka]

Your task is not so easy. First, you never defined what is your "high power".
Once you define it, you can calculate the voltage across the line impedance, say 50 Ohms.
This calculated voltage will exist between the line and ground if the line is matched; it means there is no standing-wave on it.
If your line is mismatched, the peak voltage across the line can be much higher than the calculated for a matched line.
A mismatched line, with an open or shorted end, can drive the peak voltage to > 10x the calculated voltage.
Good luck!

 

[cmkrkmz]

Wrong. For a microstrip line, the signal is between the line and the ground below, and the line impedance is set by the line width and the distance to the ground below.

Microstrip Line Calculator | em: talk

---------- Post added at 08:51 ---------- Previous post was at 08:47 ----------



OK, we all might have misunderstood your initial question. You ask about the distance between a microstrip conductor and some other (grounded) metal on the same layer?

thank you for posts.
i mean 500 W or 1 kW by saying "high power".
yes volker, i ask about the distance between microstrip and grounded metal on the same layer.