A modulated sub-carrier technique of measuring microwave attenuation

A method of measuring microwave attenuation is proposed which has the advantages of an i.f. substitution method with single-sideband operation. However, ordinary amplitude modulation is used, and neither the carrier nor one of the sidebands needs to be suppressed. Two versions of this method are described and some operational hints are given. One of these versions is capable of high accuracy with commercially available equipment. The proposed method was tested by measuring the relative attenuation of a microwave variable attenuator at 9.3897 Gc/s, attaining a precision of 0.0001 dB at 0.01 dB and 0.2 dB at 50dB. The measurements are compared with measurements performed by other methods. A special comparison with values obtained from d.c. substitution techniques was made in which environmental effects were largely eliminated. Factors affecting the accuracy of measurements made by this technique are discussed. Some of the precautions necessary to attain high accuracy are given.