Microwave electrostatic wattmeter

The paper describes a new instrument which operates as the microwave equivalent of the well known low-frequency electrostatic wattmeter. The torque on the moving vane depends on the forces arising simultaneously from both the electric and magnetic components of the field carrying the power, with the consequence that accurate measurements can be made for any standing-wave ration up to about 6 : 1. A theoretical analysis of the operation of the instrument, supported by experimental information derived from a model, shows the practicability of the design, particularly as a reference standard. Using a photovoltaic cell for recording small deflections, the wattmeter operating at Xband is capable of an accuracy of ±2% when measuring powers of about 100mW, and it may be calibrated on an absolute basis.