  Rational function approximations find applications in many areas including
macro-modeling of high-frequency circuits, model order reduction for controller
design, interpolation and extrapolation of system responses, surrogate models
for high-energy physics, and approximation of elementary mathematical
functions. The unknown denominator polynomial of the model results in a
non-linear problem, which can be replaced with successive solutions of
linearized problems following the Sanathanan-Koerner (SK) iteration. An
orthogonal basis can be obtained based on Arnoldi resulting in a stabilized SK
iteration. We present an extension of the stabilized SK, called Orthogonal
Rational Approximation (ORA), which ensures real polynomial coefficients and
stable poles for realizability of electrical networks. We also introduce an
efficient implementation of ORA for multi-port networks based on a block QR
decomposition.
