Note on wave-guide attenuators

For an application in a 3-cm signal generator it was desirable to include in the wave-guide circuit both fixed and variable attenuators and it was essential that these attenuators should be in a form suitable for large-scale production. Fixed attenuators of values in the range 5 to 20 db were required and provided that the power absorption was limited to the order of 1 W a satisfactory solution was found. At dissipations greater than 1 W the attenuators were not reliable owing to thermal instability of the material employed. The same material was also used for variable attenuators covering the range 0¿20 db, but a better solution has eventually been found in which the power-handling capacity is limited only by the necessity of preventing physical damage, and a very much lower temperature-coefficient has been obtained. A variable attenuator for use at high powers has also been developed in which the power is absorbed in flowing water.