Objectives:
1. To understand the function of transmission line stubs.
2. To perform impedance matching graphically using the smith chart utility in ADS.
3. To calculate the transmission line parameters graphically using Smith chart.
Smith Chart utility in ADS
This Design-Guide Utility in ADS provides full smith chart capabilities, synthesis of matching
networks, allowing impedance matching and plotting of constant Gain, Q, VSWR, and Noise circles.
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From the Design-Guide menu on the ADS Schematic window, select (Filters Design-Guide)
> Utilities > Smith Chart Control Window.
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The figure shown above is a snapshot view for the Smith chart utility. It has the capability of
entering the data-points in several formats.
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It also can display the values of the designed matching network as well as designing it
automatically using the (Smart Components option).
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The basic elements of this program are briefly described in the following statements. The
complete documentations set of the tool are already placed on the intranet directory.
1. The components palette:
This palette contains lumped elements in
serial and shunt connection as well as
transmission line segments and stubs for
matching purpose.
2. The Chart Area:
The Smith Chart Drawing Area is the central focus of the Smith Chart Utility. In this area the full
functionality of a smith chart can be utilized. Gain, VSWR, Q, and Stability circles can easily be
plotted by simply entering S parameters and then selecting the corresponding menu items. Complex
impedance matching is also done in this area by using any of the available passive elements or
transmission lines.
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3. The Network Area:
The Smith Chart Network Area is a quick and easy reference to both viewing your matching
network and seeing its performance with the given data. A real-time frequency response is plotted
for each change made on the smith chart. The scattering parameters in amplitude and phase formats
are there as well.
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Scattering parameters in
amplitude and phase
Frequency range
The matching network
to be implemented is
displayed here
The scattering parameters in amplitude and phase formats are there as well as you can find them on
the top right edge of the image.
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Impedance Matching:
It is the practice of attempting to make the output impedance of a source equal to the input
impedance of the load to which it is ultimately connected, usually in order to maximize the power
transfer and minimize reflections from the load and this is known as load impedance matching.
Other type of matching is well performed for the generating source to the transmission line in the
same manner also to minimize the reflections from its internal impedance and maximize power
transfer.
Impedance matching in ADS using Smith Chart Utility:
Hence, using Smith Chart as a powerful tool in allocating impedance over it and showing the effect
of adding any impedance "resistive or inductive or capacitive", It can be used in matching by
adding circuit elements that modify the input impedance till we match the load to the characteristic
impedance of the transmission line Zo.
In this Utility, Elements are grabbed from the components palette and added to the allocated
impedance on the chart where the chart contains two shaped one for the load impedance and the
other for the source impedance and you can move any of them on the chart according to its value
and in the matching case both shapes are on the origin as shown in figure
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For load impedance matching the load is moved from the origin by using the cursor or by setting the
value of load impedance down the chart area "entering it in a normalized value and entering the
value of the characteristic impedance down the network area".
L-C matching:
This is a matching type for the load and source impedances using lumped circuit elements which are
inductors and capacitors.
Resistors aren't used in matching due to there power consumption which violates the main aim of
matching which is maximizing the power transfer to the load.
After allocating ZL, Inductor L can be grabbed or a capacitor C so to move over a circle with a
constant resistive part.
Each element grabbed series L or parallel L or series C or parallel C is connected to the load one
after the other forming the matching network till you reach the origin which expresses the matching
case where the input impedance seen from " matching network + load " is Zo which is the line
characteristic impedance.
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Using Single shunt stub
Draw the G=1 circle; admittance=1+j*B
Click on circles/options.
Set frequency value & impedance; input the value of the load.
Start your design using an appropriate length transmission line then the shunt stub.
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