A simple waveguide directional coupler

This paper discusses an easily constructed waveguide-to-waveguide directional coupler. Constant coupling and directivity are obtained over a wide frequency band. The coupling factor and directivity are calculated for two typical cases for waveguide of external dimensions 3 in by 1¿ in. In addition an expression is derived for the frequency sensitivity of the device, showing that the rate of change of coupling with frequency is almost zero in the middle of the useful range of the waveguide for H10 transmission.