A microwave power meter based on a crystal diode

Abstract

Microwave and high-frequency power meters based on bolometer and thermistor bridges are widely used at the present time. In these instruments, the action on the thermal element of the high-frequency power arriving from outside is compensated by a change in the dc power dissipated in the thermal element [1, 2]. Microwave and high-frequency power meters based on crystal diodes, despite a number of advantages (their high sensitivity, low inertia, etc.), have not found wide application because of the considerable measurement error due to temperature and time instability of the parameters of the crystal diodes, and also due to the difficulties involved in constructing circuits based on diodes to compensate the high-frequency power being measured by a change in the dc power. In this connection, we consider below a circuit for a power meter based on a crystal diode, in which the microwave (or high-frequency) power acting on the crystal is replaced by the power from a special low-frequency generator built into the instrument, which can make measurements comparatively accurately [2]. The simplified circuit of the power meter is shown in the figure. The power meter operates as follows. When there is synchronous switching of HS and LS at a frequency of 10 Hz, a pulsed voltage is generated at terminal 1 of the switch, corresponding to the microwave power P h , while at terminal 2 LS generates a pulsed voltage corresponding to the substituting low-frequency power P s . The difference of these voltages is separated in the comparison circuit, from which, after amplification by the automatic power regulating system (SA), a signal e p is generated for controlling the substituting power of the generator RG: