CLASS OF NONUNIFORM COUPLED TRANSMISSION LINES AND THEIR EQUIVALENT CIRCUITS.

The distributed coupled line is an important circuit element in microwave circuits and is widely used in filters, impedance transformers, directional couplers, phase shifters, etc. Y-type and Z-type parabolic-taper single-mode transmission lines and their equivalent circuits are first discussed. Then, by superposition of two of the above single modes, the TEM mode along a parabolic-taper coupled transmission line (PTCTL) is analyzed. According to the choice of Y-type or Z-type for tapered single modes and the choice of combinations of balanced-unbalanced modes or open-short line modes as two independent superposed modes, there can be six types of PTCTL. Their equivalent circuits are also easily shown.