A microwave electrostatic wattmeter

The paper describes an instrument incorporating a metal vane suspended in a waveguide as a means of measuring the power transmitted. The arrangement is electrically equivalent to the electrostatic wattmeter, well known in low-frequency applications, and in principle it has the particular merit of being able to record true power consumed by a load over a wide range of standing-wave ratio. The vane experiences a resultant torque whose magnitude and direction are dependent on the net power flow. A series resistive element has to be introduced into the waveguide at the point where the suspended vane is located, and there is therefore an initial deflection corresponding approximately to half the power consumed by that resistance and representing about 5% of the load power.