S parameters of lossy transmission line in a Z0 system

Hi,

I wanted to calculate S parameters of a 'lossy' transmission line in 'Z0 system'. I am able to calculate S11.
I am finding it difficult to calculate S12.

Can someone please help me in finding it.

[I have seen a paper which says these derivations are available in book "K.C. Gupta, R. Grag, and R. Chada, Computer Aided Design of
Microwave Circuits." I do not have the book with me.]


Best Regards,
analog_newbie.

Hi analog,

there are few things regarding your post: S11 is the reflection at port 1 of the signal transmited into a 2port network and S12 or S21 is the gain, the signal transmited from port 1 to port 2.
S12(db)=20*log(Vout), where Vout is the voltage at the output.

If this is not enough, see the photos and the formulas.
http://images.elektroda.net/19_1330520846.jpg
http://images.elektroda.net/67_1330521119.jpg
http://images.elektroda.net/27_1330521277.jpg

I hope this will help you to understand how to calculate....Good luck.

I know those things. My question is how is it done for Tx line.
Thank you very much .
Vasu.

Calculate ... based on what?

First of all,Hi

If you meassure a Tx with a Vector Network Analyzer you can see in dB the value of S12 or S21 as magnitude.And then you know the magnitude is 20*log(S12), resulting S12.
If you want to calculate, outside what i said in the first replay , i don't know how yet.

I want S12 in terms of length of line, characteristic impedance, propagation constant and reference impedance.

I found this in a textbook:

ABCD parameters for a lossy line with propagation constant gamma and line impedance Z1:

Conversion from ABCD params to S-params:

Do you want to calculate it from a measurement or from theoretically formulas?

I guess a lot of people miss out that if your antenna has one port, you can only measure S11. For any other parameters such as s12 or s21, you must have 2 port antenna.

If you want to measure s12 on a single port antenna, you can only do this way....

Simulation Wise :
For example in HFSS, design 2 identical antennas and put them apart more than the minimum far field. Just run the simulation and you can plot the S parameters by choosing the type of ports eg s11,s12 or s21 or s22.

Practically :
First, you must have 2 identical antennas, one is as RX port and the other is at TX port. Treat the RX port as port 1 and TX port as port 2 then you can calculate it.

S12 means signal goes in port 1 and measure port 2 transmission coefficient by the way.

But when you said u want to measure or you want to calculate?

---------- Post added at 18:08 ---------- Previous post was at 18:04 ----------

By the way you should realise all this parameters are for antenna measurements.

The losslessness can be due to many factors...so the parameters you mentioned are for antennas!

By the way you should realise that s12 means the ratio between power transmitted at port 2 and power received at port 1.

So you can only equate s12 to power and not length of line. The line has an equal characteristic impedance which means it's assume to be not lossy.

So if your antenna is lossy, that means ur antenna and your characteristic impedance are not matched and it's not a matter of calculating s-parameters but it's a matter of matching your load to your characteris impedance!

Antenna? The question was about calculating transmission line S11/S21 from length & impedance, see #6

Nonsense.

Thank you so very much