4 port S - Parameters in MATLAB

Hi everyone,

i have to split 4 port S-Parameters (*.s4p) into two mirror symmetrical parts with MATLAB. I read some papers from Agilent about this topic, but i couldn't find any useful information.
S21(or S12) of splitted S-Parameters are the half of measured data. But problem is reflection coefficients.

For reflection coefficients:

At the first I transformed single ended S-Parameters to mixed-mode. Then I converted differential mode quadrant transmission coefficients to time domain with chirp z Transformation and determined the total electrical length of Thru circuit.
The last step is the reflection coefficients. I have converted differential mode reflection coefficients to time domain and gated this time function by the half of electrical delay. The modified time domain data transformed back to frequency domain. The result of last transformation is the splitted S-Parameter reflection coefficients.

So, my problem is with time gating. As a time gating function I use the "brick-wall function". The next question is again with gating. have i convolve time domain reflection coefficients with gating function ?

please advice
thanks