Magnetic Field Generation and B-Dot Sensor Characterization in the High Frequency Band

Abstract

Designing a high frequency (HF) magnetic field direction finding (DF) array for use onboard a military aircraft is the challenge that drives the effort of the research presented. The frequency range of interest, 2-32 MHz, has a maximum wavelength (150 meters) that exceeds the maximum length of any platform in the USAF inventory. The large wavelengths in the HF range make it difficult to accurately estimate from which direction a magnetic field is emitting. Accurate DF estimates are necessary for search and rescue operations and geolocating RF emitters of interest. The primary goal of this research is to characterize the performance of the MGL-S8A (Multi-Gap loop) B-Dot sensor. Although the sensors are designed to operate at frequencies above 5 GHz, their small size and potential to accurately detect magnetic fields in the 2-32 MHz range make them likely to be one type of an ensemble of sensors in the design of a HF DF array. The sensors are characterized in the azimuthal angles of 0, 45, -45, 90, and -90 degrees. Each sensor is characterized using two different types of magnetic field generators: a transverse electromagnetic (TEM) cell and a Helmholtz coil. The TEM cell generates a consistent magnetic field that acts as the input to the B-Dot sensor. The second type of magnetic field generator used, which is the secondary objective of this research, is a Helmholtz coil. An ideally designed Helmholtz coil is intended to be an inexpensive alternative to help in the characterization of B-Dot sensors in the HF range. The sensors can accurately measure electromagnetic (EM) fields in the HF range. Although the detection capability of the sensors is good, small differences between the 0 and 45 degree measurements may make it difficult for the sensors to be used in a DF array.