MATLAB: How to bisect S-parameters in an S2P file into two equal halves using RF Toolbox R2015a

RF Toolbox

I have a network, say "N", which consists of two identical, cascaded networks, say "N1" and "N2". I have an S2P file that represents S-parameters of the network "N". I would like to identify the S-parameters of each of the original sub-networks ("N1" or "N2", which are identical). How can I identify S-parameters of two identical networks in a cascaded connection from the S-parameters of the resultant network?

Best Answer

(1) It is important to note that there may not be a unique solution to this problem. In other words, there may exist many "N1" (or "N2") networks that are equivalent to the same original "N", when cascaded. The attached script "demo_multiple_S_param_solution.m" demonstrates this further. It shows that for a given network "N" with S-parameters [0 1;1 0], there exist two solutions [0 1;1 0] and [0 -1;-1 0] which satisfy the requirement.

(2) Also, please keep in mind that for some edge cases, there may not exist a solution at all.

(3) Keeping both (1) and (2) in mind, if there is at least one solution, it is possible to find it. The example shown in the attached script "demo_split_S_param_cascaded.m" uses ABCD parameters to find it. For most data sets, you can convert between S and ABCD parameters using the "s2abcd" and "abcd2s" functions in the RF Toolbox.

The ABCD parameters have a useful property: when you cascade two networks, you can discover the resulting ABCD parameters by multiplying the original ABCD parameters of the individual networks. Hence, we can find the ABCD parameters of "N1" and "N2" by taking the matrix square root of the ABCD parameters of "N".

As shown in the attached script "demo_split_S_param_cascaded.m", the general workflow is as follows: # For each frequency, convert the S-parameters of "N" to ABCD-parameters using the "s2abcd" function. # Take the square root of that matrix using the "sqrtm" function, which gives the ABCD-parameters of the "N1" network. # Finally, convert those ABCD-parameters into S-parameters using the "abcd2s" function.

Related Solutions

MATLAB: How to pass Z-parameters as a parameter input to the plot function of the rfckt.cascade object within the RF Toolbox 2.3 (R2008a)

The ability to do pass Z-parameters as input arguments to the "plot" function of the "rfckt.cascade" object is not available in the RF Toolbox.

As a workaround, use the S2Z function to convert S-parameters from the "AnalyzedResult.S_Parameter" field of the "rfckt.cascade" object into the equivalent Z parameters. Then, replace the "AnalyzedResult.S_Parameter" with the output of the S2Z function and plot the results of the "rfckt" object.

MATLAB: How to cascade a four port device with a two port device using rfckt objects in RF Toolbox

Unlike RF Blockset which has a 'Coupler' block for Simulink, there is no four port device rfckt object. In RF Toolbox, rfckt circuit objects are designed for chain of objects, i.e. we are limited to two port networks. As a workaround, if you could represent the Coupler as a 2 port network touchstone file, it will be possible to read the file and create a 'rfckt.passive' element with it. And then we can continue do the RF analysis on that network.

Please refer to the sample scripts below demonstrating this using two approaches -

1. Use the 'nport' object which reads both S-parameters and noise data from a Touchstone file. Then cascade them using an 'rfbudget' object. This sample script is the recommended and approach and it uses some functions which were released in MATLAB R2017a.

%%Using NEW nport objects (Recommended)/Approach 1
%%Read in a 3 Port coupler 

S3 = sparameters('default.s3p');

Coupler to to 2-port nport

S2 = snp2smp(S3);
rfwrite(S2, 'coupler2port.s2p')
% Creating a nport object
Coupler2port = nport('coupler2port.s2p');
% Note that coupler does not have noise of its own.
ckt1 = nport('default.s2p'); % Other 2 port sparameter device

% Noise Data can be viewed by doing ckt1.NoiseData
%%CASCADE

ckt_cascade = rfbudget([Coupler2port ckt1],[2e9:1e9:10e9],-30,10);
show(ckt_cascade);

To export the network into Simulink, i.e. RF Blockset please uncomment and execute the command below

% exportRFBlockset(ckt_cascade)

2. Use the 'rfckt.amplifier' object which contains both S-parameter and noise data. Then cascade them using 'rfckt.cascade'. This approach is not recommended, as it might be not available in future releases.

%%Using OLD rfckt objects /Approach 2
%%Read in a 3 Port coupler 
ckt = read(rfckt.passive,'default.s3p'); % This only works for passive data
s3p = ckt.NetworkData.Data;
Z0 = ckt.NetworkData.Z0;

Coupler to to 2-port rfckt.amplifier

s2p = snp2smp(s3p,Z0);
% Creating a rfckt object
rfwrite(s2p,ckt.NetworkData.Freq,'coupler2port_ckt.s2p')
Coupler2port = read(rfckt.amplifier,'coupler2port_ckt.s2p');
ckt1 = read(rfckt.amplifier,'default.s2p'); % Other 2 port sparameter device
%%CASCADE
ckt_cascade = rfckt.cascade('Ckts', {Coupler2port, ckt1});
analyze(ckt_cascade, 2.9e9)

Best Answer

Related Solutions

MATLAB: How to pass Z-parameters as a parameter input to the plot function of the rfckt.cascade object within the RF Toolbox 2.3 (R2008a)

MATLAB: How to cascade a four port device with a two port device using rfckt objects in RF Toolbox

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