Branch line directional coupler having an impedance matching network connected to a port

摘要

The invention is an improvement over the conventional branch guide directional coupler and gives better performance by providing flatter coupling over a broader band. A branch guide (line) directional coupler fundamentally is a four port electrical network. The invention improves the performance of the conventional branch guide coupler by employing matching devices at the ports of the fundamental network. In most embodiments of the invention, it is contemplated that matching devices will be used at each of the ports and that all those matching devices will be of like construction. However, it is not essential that a matching device be employed at every port nor is it essential that all the matching devices be of like construction. For example, in some embodiments of the invention, matching structures need be employed only at the output ports. In the stripline and microstrip embodiments of the invention the matching device can be formed by a half wavelength open- circuited stub in combination with a quarter wavelength transformer or by a short-circuited quarter wavelength stub in combination with a quarter wavelength transformer. Although the invention is described principally in strip line or microstrip form, the invention can also be embodied in waveguide or coaxial form.