WATTMETER
PROBLEM TO BE SOLVED: To reduce the influence of a differential heating at a heat-measuring bridge by constituting a wattmeter of the heat-measuring bridge, a servo circuit, a compensation circuit, etc., and constituting the compensation circuit so as to hold a sum of a measurement power and a commo...
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Zusammenfassung: | PROBLEM TO BE SOLVED: To reduce the influence of a differential heating at a heat-measuring bridge by constituting a wattmeter of the heat-measuring bridge, a servo circuit, a compensation circuit, etc., and constituting the compensation circuit so as to hold a sum of a measurement power and a common mode power at a constant value. SOLUTION: A heat-measuring bridge 31 outputs difference signals 40, 41 which are obtained from a bias signal 47 and have an amplitude proportional to a power level difference of an RF signal and an equilibrium signal 57. Servo circuits 42-45, 52, 56 are coupled to the difference signals 40, 41 from the heat-measuring bridge 31, generate the equilibrium signal 57, adjusts a power level of the signal and minimizes an amplitude difference of the difference signals 40, 41. A compensation circuit 60 receiving the equilibrium signal 57 outputs a compensation output 74. Isolation circuits 58, 59 each have one end connected to the compensation output 74 and the other end connected to an input power port 32 and a comparison port 33. The compensation circuit 60 supplies an additional power of the same amount to the input power port 32 and comparison port 33, and adjusts the additional power so that a sum of the additional power a power of the RF signal and a power of the equilibrium signal 57 becomes constant. |
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