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Stability factor K of two-port network



[k,b1,b2,delta] = stabilityk(s_params) calculates and returns the stability factor, k, and the conditions b1, b2, and delta for the two-port network.

[k,b1,b2,delta] = stabilityk(hs) calculates and returns the stability factor and stability conditions for the two-port network represented by the S-parameter object hs.


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Examine the stability of network data from a file by first calculating the stability factor.

S = sparameters('passive.s2p');
s_params = S.Parameters;
[k,b1,b2,delta] = stabilityk(s_params);

Check stability criteria.

stability_index = (k>1)&(abs(delta)<1);
is_stable = all(stability_index)
is_stable = logical

List frequencies with unstable S-parameters.

freq = S.Frequencies;
freq_unstable = freq(~stability_index)
freq_unstable =

  0x1 empty double column vector

Input Arguments

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Two-port S-parameters, specified as a complex 2-by-2-by-M array. M is the number of two-port S-parameters.

Data Types: double

Two-port network, specified as an S-parameter object.

Data Types: function_handle


Necessary and sufficient conditions for stability are k>1 and abs(delta)<1. stabilityk calculates the outputs using the equations



  • S11, S12, S21, and S22 are S-parameters from the input argument s_params.

  • Δ is a vector whose members are the determinants of the M 2-port S-parameter matrices:


The function performs these calculations element-wise for each of the M S-parameter matrices in s_params.


[1] Gonzalez, Guillermo. Microwave Transistor Amplifiers: Analysis and Design. 2nd ed. Upper Saddle River, N.J: Prentice Hall, 1997.

See Also

Introduced before R2006a