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I never intended to add a Smith chart to my S-parameter plotter. I can appreciate how useful they must have been before computers, but I don't see their value today. A computer program, especially one with automatic optimization, can make quick work of a complex matching problem. However, since I see references to Smith charts here all the time, before I dismiss them I thought I should ask why people use them. What do they offer that rectangular plots versus frequency don't?



Brian

Yes, and if you let the PC do all the optimization work, what have you
learned? Not much other than how to use the PC for the applications.
Rectangular plots vs. frequency, Bode plots, give you absolutely no
information of the complex portions of impedances. Yea, poles and zeros.
They're like an SWR meter. The VECTOR reflection coefficient gives you far
more information than just frequency response!! Bode plots address
frequency response, and, yes, some additional information. But they are
certainly not as powerful as the Smith Charts when it comes to dealing with
complex sources and loads. By complex, I mean the reactive components of a
circuit, not a "complex" circuit.

Sorry, I live on the Smith Chart and have no intention of letting the PC do
all the work. What have I missed? Everything.....

EXAMPLE: The EE students at CSU up in Fort Collins, Colorado, "learn"
electronics sitting in front of PCs doing simulations. I've worked with a
few of them before retiring. They are useless in both designing and
troubleshooting. If it were up to me, they would not have been hired!
They can't even put Ohm's Law on the white board, let alone use it!!!!
Sure, they learn how to use the modeling applications. But those change.
After a decade or so, they're useless at even running the newer
applications. Then they need to find a new career.

I'll stick with my Smith Charts, thank you.......

Dave - W?LEV

On Sat, Apr 26, 2025 at 11:18?PM Brian Beezley via groups.io <k6sti=
[email protected]> wrote:

I never intended to add a Smith chart to my S-parameter plotter. I can
appreciate how useful they must have been before computers, but I don't see
their value today. A computer program, especially one with automatic
optimization, can make quick work of a complex matching problem. However,
since I see references to Smith charts here all the time, before I dismiss
them I thought I should ask why people use them. What do they offer that
rectangular plots versus frequency don't?



Brian

--

*Dave - W?LEV*


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Dave - W?LEV

After working with Smith charts for awhile, and understanding them - they provide in one 'glance' a visualization of the complex impedance across frequency, at the same time as a visualization of the SWR across frequency. And at the same time, for a length of transmission line, you can see the wavelengths/half-wavelengths directly. I don't know of another single plot that can do that (I guess you can overlay multiple traces on the same XY plot to acheive it, but it is IMO not as convenient).
Stan KC7XE

On Sat, Apr 26, 2025 at 04:32 PM, W0LEV wrote:

The VECTOR reflection coefficient gives you far
more information than just frequency response!!

If you can plot the real and imaginary parts of an S-parameter as well as magnitude, phase, and SWR, what additional information does a Smith chart provide? Is the advantage that you get SWR and impedance in one curve as Stan suggests?

Brian

Convenience for graphical design of a matching network. There’s also sort of a qualitative thing that you recognize particular “shapes” on the chart as having particular significance.

And, if you’re tuning a filter by turning a screw, sometimes seeing the Smith chart in real time is more “intuitive” in some sense. I tune filters looking at magnitude S11 and S22 and S21. For a three section filter, you can see the three resonances, and looking from one end or the other tends to emphasize the section closest to the port you’re looking at.

These days, with computers, seeing the Smith chart isn’t as useful.
I use plots of magnitude and phase for design. And I work with a lot of more than one port systems, for which the Smith chart is less useful. For instance, if you’re looking at the coupling among antennas in a phased array.