problem of harmonic impedance

[terazety]

Hi,
I want to test the harmonic impedance of a transmission line segment.
But I don't know how to do the simulation?

What kind of simulation do I need?

Looking forward to your reply.

Thank you.

Jim

 

[WimRFP]

Hello Jim,

What do you mean with the word "harmonic"? When you mean impedance for sinusoidal excitation (steady state) there are various ways, depending on your simulator.

What simulators do you have and which one has your preference for this simulation?

 

[pathto_teraze]

Hi,
I am using HSPICE for simulation.
I have a transmission line segment in my design.
I want to test the impedance variation of this piece of transmission line vs. frequency.
So I want to do a frequency sweep to get the impedance of this tline for each frequency.

I search online and find I can do a harmonic analysis to get the harmonic impedance that I want.

Am I right?

Thanks.

 

[WimRFP]

Hello,

SPICE has both models for lossy transmission line (O) and lossless transmission line (T). The .AC command gives you the frequency sweep simulation.

Before you start the simulation, you need to know the transmission line parameters that is: characteristic impedance and electrical length (or delay time). When you want to use the lossy line, you need to know the inductance/m, capacitance/m and resistance/m. You can derive that from the characteristic impedance and propagation velocity of your transmission line (except for the resistance/m).

For the simulation: Some spice programs have a network analyzer feature. If you don’t have that, you can use a current source of 1A and put a voltage probe across the current source. The voltage (phase and amplitude) equals the impedance of the transmission line segment.

If you use the lossless transmission line model , make sure to add a T or PI attenuator to model the losses of your line. When you use the lossy line, you have to play with the resistance/m to make sure the loss of your simulated line equals the actual loss. You can make a first guess based in the skin depth and size of inner conductor of the transmission line.

You can do it empirically by terminating the piece of line with its Z0 and determine the transmission (output voltage/input voltage). From there you can calculate the loss/m of your simulated line based on the length of the line.

Hope this helps you a bit.

 

[Element_115]

Just do all your normal Sims, but sweep the Frequencies from your
lowest desired freq --> to n * (Max Desired Freq).

Look at the plots to see how the Harmonics perform.
You can plot S11 & S22 to read what the Impedance is at each
Harmonic, and look at the S21. You will see how close the HARM's get
to the Fundamental S21.

 

[WimRFP]

Hello,

When you use a non-terminated transmission line with low loss, the high and low impedance regions are narrow band, so you need to use sufficient frequency points to see all the details of impedance versus frequency curve.

Best is (when you did a frequency sweep) to double the number of frequency points and see whether the result changes. When it changes significantly, double the number of points again.