This International. Standard is applicable to the sweep frequency method used for the measurement of return loss on waveguide and waveguide assemblies. Return loss is defined as ar = 20 log (ui/ur) dB where u. is the magnitude of the incident wave; 1 ur is the magnitude of the reflected wave. Return loss is related to the reflection coefficient, r, by: r = (ur/ui) r = 10-(ar/20) Fundamentally the method involves measuring the amplitude of the reflected waveguide under test (WUT) input by means of a reflectometer device. The reflected wave can be compared with the total reflected wave under conditions, attenuated by a calibrated attenuator, or it can be compared with wave by means of reflectometer.