SMITH CHART INFORMATION
Many Amateurs do not have the equipment, knowledge and sometimes the inclination or time to measure the complex impedance of the antenna's they read about and build.
The old standby "VSWR" or commonly referred to as "SWR" is their only reference to matching. If you do a lot of antenna experimentation as I, and I'm sure you do like all hams, you must know the antennas Impedance, where it's resonant and the information to decide, if necessary, on the type of matching network to use .
I don't mean an "ATU" sitting on your desk here, as we want to deliver all the R.F. we generated to the antenna or load. There are numerous commercial impedance measuring equipments advertised and antenna designs you can build. The ARRL publications, to name but a few, are full of them. Which ever way you choose to get the impedance data is immaterial. But once you get it, it will open your world as to what is really going on with your antenna.
In addition, there are many software programs to do the Smith Chart calculations; but you need that impedance data to plug in.
The Smith Chart performs many calculations, its not limited to only showing an antennas impedance. I have been using the Smith Chart from back in the late '50s, when the LPDA craze hit, we were doing a lot of R&D work and were constantly measuring data and reducing it onto the Smith Chart for evaluation. Typically for our use, it will show the impedance over the frequency range of interest including the resonance point, where the impedance data crosses the real axis, not minimum VSWR.
If your antenna is to short or too long, it's much nicer to calculate the difference required than use the cut, add, cut approach. Once you have established resonance at the frequency required, it's just a matter of determining the type of matching required as determined by the impedance at resonance.
Using the Smith Chart to help match your antenna is but one important function it can perform for you. But lets start at the beginning and learn how to do the simple stuff first.The Web Site(s) presented under the "Helpful Links for Hams" can show you the basic use of the chart and what it can do. Review these examples and see what you think. Once you get the basics down, it's a piece of cake, and your antenna might radiate just a little better.