Directional coupler for separation of signals in two frequency bands

Abstract

A directional coupler is provided which has an appropriately dimensioned principle waveguide with a frequency dependent reactive boundary interior surface such that the principle waveguide is suitable to simultaneously: (i) support, without depolarization, effective propagation of first signals in a high frequency band at a HE11 mode with greater concentration of energy near the axis of the principle waveguide than near the interior surface and no effective propagation of first signals at any unwanted mode, and (ii) support, without depolarization, effective propagation of second signals in a lower frequency band at a EH11 mode having a greater concentration of energy near the interior surface of the principle waveguide than near the axis and no effective propagation of second signals at any unwanted mode. Four identical secondary waveguides are placed symmetrically at equal radial intervals about the outside perimeter of the principle waveguide with the longitudinal axis of each of the secondary waveguides running parallel to the longitudinal axis of the principle waveguide. A plurality of coupling units are disposed at longitudinal intervals along the principle waveguide with each coupling unit comprising four aperture-like structures interconnecting a respective one of the secondary waveguides and the principle waveguide for exchanging energy in the first signals between the secondary waveguides and the principle waveguide. This structure provides a directional coupler for separation of signals in the first and second frequency bands while preserving their polarization characteristics.