I am a FEKO user too. Well, the mat2ascii.exe utility can be used via Command Prompt and the data can be stored in a *.txt file, however the generated file will only contain the rows, columns, real part and imaginary part of the impedance matrix FOR THE FIRST FREQUENCY OF THE SIMULATION. In other words, if you want to simulate at a frequency range (multiple frequencies) the generated *.mat file contains the data of every impedance matrix, however the mat2ascii.exe utility converts only the data of the first impedance matrix of the simulation to *.txt file. Maybe the *.mat file can be easily read in a FORTRAN environment but I don't know that. I have tried to use the f2matlab routine created by Prof. Ben Barrowes, but it failed. I am no expert in programming, though.
*IMPORTANT: There might be a mistake in the *.txt file generated by mat2ascii.exe. It contains some explanatory text in the beginning and then it contains 4 columns with the data of the first frequency impedance matrix. The first column has the numbers of rows, the second has the numbers of columns, the third has the elements of R matrix (real part) and the fourth has the numbers of X matrix (imaginary part). I believe that the third column should be labeled as imaginary and the fourth as real, because the very first element of the R matrix should always be a positive number (it belongs to the main diagonal and R is positive definite), but in my case it is negative.