Directional coupler having interdigital comb electrodes

Claim 1

A directional coupler comprising a dielectric substrate having two opposing faces, a ground sheet electrode on one face of said substrate, first and second elongated bus bars disposed in spaced relation to one another on the other face of said substrate, a first series of finger electrodes extending from said first bus bar at spaced locations distributed along substantially the entire length of said first bus bar, said first series of finger electrodes being disposed transverse to the direction of elongation of said first bus bar and projecting therefrom toward said second bus bar, a second series of finger electrodes extending from said second bus bar at spaced locations distributed along substantially the entire length of said second bus bar, said second series of finger electrodes being disposed transverse to the direction of elongation of said second bus bar and projecting therefrom toward said first bus bar, said first bus bar and its respective first series of finger electrodes being separated from said second bus bar and its respective second finger electrodes to form first and second electrically isolated interdigital comb structures which are capacitively coupled to one another, means providing an input port and an output port for each of said comb structures, said input and output ports being disposed at opposite ends of each of said bus bars respectively for applying signals to and extracting signals from the coupler, the two output ports for said two comb structures being located at adjacent ends of said first and second bus bars respectively, whereby a proportion of signal power applied to the input port at one end of one of said comb structures is coupled to the remote output port at the other end of the other comb structure.