THE DEFINITION AND COMPUTATION OF MODAL CHARACTERISTIC IMPEDANCE IN QUASI-TEM COUPLED TRANSMISSION-LINES

The quasi-TEM analysis of systems of lossless coupled transmission lin es in an inhomogeneous medium is reviewed. Starting from the generaliz ed telegrapher's equations, the characteristic impedance of the normal modes is defined and computed according to the three usual definition s for the single-line case: power-current, power-voltage and voltage-c urrent. Unlike the quasi-TEM single-line case, it is shown that the th ree definitions lead in general to different modal characteristic impe dance values. Theoretical results are then confirmed by some numerical examples on two and three coupled-lines systems.