apertures 27 the amount of power 37 exiting a third port 39 and power 41 exiting an opposite fourth port 43 of the second waveguide section 17 may be controlled as is well known in the waveguide art with proper termination of the third port 39 power 19 entering the first port 21 can be made to couple to the second waveguide section 17 and exit from the fourth port 43 at a maximum level set by the size of the apertures 27 by properly applying bias potential to selected diodes mounted on the reflective absorptive material the coupler 11 output power 41 can be switched at high speeds from zero to any desired power level up to the maximum level or varied more slowly in any desired range from zero to the aforementioned maximum level the application of bias potential to selected diodes represented in fig2 by wires 33 may be implemented by a non unique bias power controlling circuit 51 shown in fig3 for example here a conventional bias potential supply 53 is coupled to a conventional controller circuit 55 through a cable 57 which is in turn coupled by a cable 59 to a bias header 61 fig2 of the power control coupling member 29 in operation the bias supply 53 provides a potential sufficient to either place diodes 33 in a conductive or non conductive state in a conductive state each pin diode would act as a vertical wire extending across the aperture 27 in this case the aperture is a 0 300 inch square configuration it should.