Nonsquare spectral factors via factorizations of a unitary function

AbstractWe consider the problem of parametrizing the set of nonsquare minimal spectral factors of a rational matrix function taking positive semidefinite values on the imaginary axis. The tool here is the use of factorizations of a certain type of the function W+−1W−, where W+ (resp., W−) is the minimal square spectral factor that has all its poles and zeros in the right (resp., left) halfplane