Insular waveguide directional coupler

An insular waveguide directional coupler for use in the frequency range from about 1 GHz to about 1,000 GHz comprising a conductive image plane, a first length of elongated high permittivity dielectric waveguide of finite cross section adjacent to said conductive image plane, a second length of elongated high permittivity dielectric waveguide of finite cross section adjacent to said conductive image plane and spaced from said first length of waveguide to provide a coupling region therebetween, and a thin film of synthetic organic resin disposed between and secured to said conductive image plane and said lengths of waveguide and extending laterally beyond the said lengths of waveguide and into said coupling region, said thin film being low loss in character and having a low permittivity compared with that of said lengths of waveguide, said first length of waveguide having an inlet port at one end of said coupling region and spaced away from said second length of waveguide a distance substantially greater than the distance between said lengths of waveguide in said coupling region, said first and second lengths of waveguide having respectively first and second outlet ports at the other end of said coupling region and spaced from the other length of waveguide a distance substantially greater than the distance between the lengths of waveguide in said coupling region, all of the energy injected into said inlet port being coupled from said first length of waveguide across said coupling region to said second length of waveguide and out said second outlet port when said coupling region has a length equivalent to an odd number of coupling lengths and all of the energy injected into said inlet port being transmitted through said coupling region to said first outlet port when saud coupling region has a length equivalent to an even number of coupling lengths.