rf power loss

anybody can give me some good method to calculate the power loss in FR4 PCB Trace design?

For example .
The RF power amp output to the antenna switch has a length about 60mm.
I worry about the long RF trace will make the power loss . I want to know ,whether have some idea to calculate the loss value accurate?

thanks very much.

You need to know the complex propagation constant (which accounts for dielectric losses) or, which is the same, the simple real complex constant and the loss tangent (tan δ).

Problem is, usually FR-4 manufacturers don't care much about losses at high frequencies, so this data is not even published.

Moreover, this can be significantly different from FR-4 manufacturer to manufacturer. To mess um a little bit more, these values are dependent on frequncy and even on the track direction (along the fibers or perpendicular to th fibers).

My suggestion (if you can do so):

- Choose an FR-4 manufacturer and stick to it;
- Manufacture a few boards (say, 4) with different line lengths;
- Test those boards on a network analyser on the band of interest;
- Extract the needed constants from those measurements.

Beware that for long microstrip traces not only the PCB losses counts.
Long traces at high frequencies on cheap PCB materials are susceptible for losing the desired impedance, and different impedance will result in a mismatch loss:

Mismatch_Loss [dB] = -10*LOG(1-Γ2)

Thanks for your kindly help.
I have seen at a bbs.
it tell me that in high frequency (1G--2GHz) use FR-4 tg = 0.035 , if the trace reach 50mm it will be about 0.7dB loss, I want to know ,how can I get the 0.7dB with math calculate?

thanks

Not easily because loss in FR4 microstrip depends upon :

- dielectric loss (tan delta)
- conductivity loss (loss due to conductivity of copper)
- radiation losses
- skin depth

Since the conductivity loss is significant and depends on the width of the line
which itself depends upon the thickness of the FR4 then the loss is not easily
calculated. Using a good Rf simulator is one way, another is to look up
measurement data.

I haven't used it, but this link may help (note that it won't be as accurate as
a proper EM simulation) :

http://mcalc.sourceforge.net/#calc

good luck !

I use agilent line calc

Does agilent ads line calc can calculat the loss?
I have never found that!

hi
do you have any idea about the cutoff frequency
and how can we find the size of antenna using cutoff frequency
Thanking you
Shahid

TX Line from AWR can calculate the loss:
http://web.awrcorp.com/Usa/Products/...ducts/TX-Line/

Yes, it's in the calculated results window on the right hand side "A_dB".

thanks for your kindly help.
best wishes

Hi,
to calculate power loss on a transmission line (like Fr4),
first calculate αd and αc
you can find some related relations for them in any microwave book like microwave engineering , D.Pozar
then you can calculate loss by following relation:
Loss=pin*(1-exp(-(αc+αd)*L)
where L is transmission line length.
Good luck