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Draw circles on Smith chart


[hlines, hsm] = circle(h, freq, type1, value1, ..., typen, valuen, hsm)


[hlines, hsm] = circle(h, freq, type1, value1, ..., typen, valuen, hsm) draws the specified circles on a Smith chart and returns the following handles:

  • hlines — A vector of handles to line objects, with one handle per circle specification.

  • hsm — The handle to the Smith chart.

The arguments to circle are:

  • h — The handle to an rfckt object.

  • freq — A single frequency point of interest.

  • type1, value1, ..., typen, valuen — The type/value pairs that specify the circles to plot.

The following table lists the supported circle type options and the definition of each option.

'Ga'Constant available power gain circle
'Gp'Constant operating power gain circle
'Stab'Stability circle
'NF'Constant noise figure circle
'R'Constant resistance circle
'X'Constant reactance circle
'G'Constant conductance circle
'B'Constant susceptance circle
'Gamma'Constant reflection magnitude circle

The following table lists the available value options for the above types of circles and the definition of each value.

'Ga'Scalar or vector of gains in dB
'Gp'Scalar or vector of gains in dB
'Stab''in' or 'source' for input/source stability circle; 'out' or 'load' for output/load stability circle
'NF'Scalar or vector of noise figures in dB
'R'Scalar or vector of normalized resistance
'X'Scalar or vector of normalized reactance
'G'Scalar or vector of normalized conductance
'B'Scalar or vector of normalized susceptance
'Gamma'Scalar or vector of non-negative reflection magnitude

hsm is an optional input argument that you can use to place circles on an existing Smith chart.


For an example of how to use the circle method, see the RF Toolbox™ example Designing Matching Networks (Part 1: Networks with an LNA and Lumped Elements).

Draw Circles on Smith Chart

Create an amplifier object from |default.s2p|.
amp = read(rfckt.amplifier,'default.s2p');

Plot the noise figure of the amplifier 1.9 GHz.

fc = 1.9e9;

See Also

Introduced in R2007b

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