A Novel Theory Expression for the Impedance of a Ferrite-Loaded CW Illuminator

The continuous wave (CW) illuminator, whose fundamentals are related to the theory of loop antennas loaded with ferrite materials, is an important facility for electromagnetic pulse (EMP) susceptibility assessment. However, existing theoretical formulas do not consider cases where ferrite materials are loaded into the loop antenna. This paper provides a new explicit theoretical formula of the impedance of a circular loop antenna loaded with ferrite materials for CW illuminator design and explores the variation regularity of its input impedance. Loading ferrite materials affects the internal impedance of the loop antenna and forces some modifications to the classical calculation procedure, resulting in an asymptotic numerical calculation method and a closed-form solution. The full-wave simulation results from CST Studio Suite show the maximum error is less than 0.99% compared to the classical theory. With ferrite material loaded, the input impedance of the loop antenna is significantly reduced and smoothed in a wide range (0< ??< 2.5). For a loop antenna with a fixed circumference, the input impedance indicates that the Q-factor decreases as the thickness of the ferrite material increases. Conversely, for a ferrite-loaded loop antenna with a constant material thickness, a larger loop circumference results in a higher Q-factor. In summary, this study provides a fast and accurate computational method for the input impedance design of CW illuminators, while also offers an effective tool for further research on the performance of ferrite-loaded loop antennas.