Strongly coupled millimeter-band waveguide directional couplers

A design technique for directional couplers, coupled through a central partition with holes paralleling the wide wall, is generalized for the case of strong coupling with 0 to 10 dB separation between the waveguides. The wave amplitude due to splitting with the propagation of the wave along the coupling system is considered; this coupling region is broken down into cascaded symmetrical sections where the phase constant is assumed to be the same in both waveguides. Analytical expressions are derived for the crosstalk attenuation between the channels, the insertion loss of the main channel and the directivity. Experimental data and values calculated using the derived formulas are compared. Both couplers can be disassembled and the partioning plate with the coupling holes and the walls are nickel plated. The agreement between experimental and calculated data is good with the formulas being applicable to programmable calculators.