The best way to learn any program is by using it. We've included many examples for you. They cover a wide range: a simple Narrow Band L-Match, a 2-3 GHz Broadband TRL Match, an 8-18 GHz Broadband FET Match, and a 16-22 GHz Complex Interstage Match.

We must assume some knowledge of the Smith Chart, and impedance matching techniques, on your part. If you are a newbie, follow along, you may well get the drift of it; its really not hard. If, after reading the next section on basic technique, and working thru the first detailed example, you still feel hazy, we suggest you obtain copies of the references listed in Appendix E for study.

All the impedance files, (we call them .IMP files), needed for the examples to follow, were transferred to the c:\mwsoft\smithmat\mwdata1 data sub-directory during the SmithMatch installation.


The Smith Chart is the best design tool ever devised for use in the creation and analysis of impedance match networks.

Every possible real impedance may be plotted on it. Across the center, there is a horizontal line; its called the axis of reals. Every point on this line represents a pure resistance. At the far left is zero ohms, and at the far right is an open circuit, (infinite ohms). The area of the chart above the center line is inductive, while the area below is capacitive.

In addition to impedances, you may also plot reflection coefficients, VSWR circles, Q-curves, and a host of other parameters. This is possible because the Smith Chart is, after all, a plot of the impedance plane onto the reflection coefficient plane.

While the basic Smith Chart is an impedance chart, it may be flipped over to become an admittance chart. If both the impedance and admittance charts are plotted together, overlaid, one upon the other, the new chart is then called an immittance chart. Despite its "complicated" look, it makes designing match networks much easier!

A popular immittance type Smith Chart used by many engineers is sold by Analog Instruments Company, New Providence, N.J. 07974. The type you want is Smith Chart Form ZY-01-N. Click to SEE a real "Immittance Chart." Caution: This file is about 2 MB in size - you might not want to view it if you're using a dial-up connection.

Design always begins with the plotting of a load impedance, in either real or complex form. The load could be anything "real," like the input of a bipolar transistor or FET, measurements taken on an antenna, etc. Once the load is plotted, its useful to then add a VSWR circle as a design aid. One then adds elements, one by one, in order to transform the load impedance into some desired impedance. In many cases, but certainly not all, the desire is to match something to "Z0," where Z0 is usually 50 ohms.

Depending on the frequency range, and other factors, you may choose to use either lumped or distributed elements, (or both), to create your match network. Lumped element design is easier. If desired, a lumped element network can be converted to distributed form, and then realized in microstrip, provided the element values are small.

Normally, when doing a lumped design, one uses capacitors and inductors, either in series, or in parallel. Resistors are rarely used as they add loss. However, one example of where a resistor may be used, is in the design of stabilization networks for active devices.

A series inductor, when added to a load, causes a rotation clockwise along a circle of constant resistance on the chart, while a shunt inductor causes rotation counter-clockwise along a circle of constant admittance.

In a similar manner, a series capacitor, added to a load, causes rotation counter-clockwise along a circle of constant resistance, while a shunt capacitor causes rotation clockwise along a circle of constant admittance.

Because of the way these components act, an immittance chart, like the type mentioned above, is often used.

High impedance, (narrow), microstrip lines act like series inductors, if they are short, while low impedance, (fat), microstrip lines, act like shunt capacitors, if they aren't too long.

With SmithMatch, you will be able to fully explore all these effects!


When you choose "(1) SmithMatch" from the Main Menu, either by pressing "1," or by using the "F1" function key, you'll enter the SmithMatch Module. The screen display will look as follows:

            SmithMatch Module

            System Z0 [<Enter>=Quit]  ? _

The system Z0 is the reference impedance used for VSWR calculations. Usually, it is 50 ohms, but it can be set to any value you desire. Z0 is almost never ever 50 ohms in an interstage match situation. Here you would want to set the reference impedance, Z0, equal to the real part of the complex source impedance when its expressed in parallel form.  In other words, say you have an impedance in the form Z +jX; a resistance in series with an inductor. You would use our Utilities+ program to do a series / parallel conversion, and express this series impedance in its equivalent complex parallel form. Instead of RS and XS, you would now have RP and XP, where RP should be used as the reference impedance in your network design.

Now, given that you're very good at what you do, as most engineers are, you might ask: "O.K., fine. I see what to use for Z0, but what do I do about XP?" Good question! What you do is use a design technique called parasitic absorption. You literally "suck in" XP, and make it the last element in the network, as referenced to the load, or the first element, as viewed by the source.

Note that, in SmithMatch, the on-screen Smith Chart is ringed with numbers. These numbers represent normalized impedances. As an example, if the chart Z0 = 50 ohms, an impedance lying right at the "0.2" marker, on the edge of the top half of the chart, would be read as: Z/Z0 = 0.2 ohms. Its un-normalized value would be Z = 0.2 X Z0 = +j10 ohms.