Design of the National Bureau of Standards Isotropic Magnetic Field Meter (MFM-10) 300 kHz to 100 MHz

摘要

A broadband magnetic field meter has been developed at the National Bureau of Standards (NBS) for the frequency range of 300 kHz to 100 MHz. The isotropic antenna unit consists of three mutually orthogonal loops, each 10 cm in diameter. The magnetic field probe described in the paper has a measurement range of 0.1 to 30 A/m. The readout of the meter is in terms of the Hermitian or 'total' magnitude of the magnetic field strength which is equal to the root-sum-square value of the three orthogonal magnetic field components at the measurement point. This magnetic field meter is nearly isotropic over its dynamic range. The electronic circuitry of the meter obtains the total magnitude of all field polarizations for all cw signals in the entire frequency band. The sensor is isotropic and is well suited for measuring the near field of an emitter, including regions of multiple reflections and standing waves. The meter can be used to monitor either the plane wave fields in the far zone of a transmitter, or the complicated fields very close to an rf leakage source. The report describes the design, performance and operating instructions for the MFM-10.