Design of wide bandwidth pyramidal microwave absorbers using ferrite composites with broad magnetic loss spectra

Abstract

Wide bandwidth microwave absorbers with a pyramidal shape and a significantly reduced thickness can be designed using high lossy ferrite materials with broad magnetic loss spectra. The microwave absorbing properties of pyramidal cone absorbers are analyzed using the transmission line approximation, which provides the reflection loss as a function of the material parameters and absorber geometry. Three types of ferrite materials (NiZn spinel ferrite, Co₂Z hexaferrite, and RuCoM hexaferrite) are used as the absorbent fillers in a rubber matrix. Among these, Co₂Z ferrite is the most suitable material for wide bandwidth pyramidal absorbers, due to its broad magnetic loss spectrum in the GHz frequency range. The optimal geometry of the pyramidal absorber is also determined using the transmission line theory. With the reduced total height of the pyramidal absorber (approximately 60 mm), a wide bandwidth (1.5-18 GHz with respect to the −20 dB reflection loss) can be realized. The proposed absorbers have a thickness advantage over the classical pyramidal ohmic absorbers; thus, they are suitable for small and semi-anechoic chambers.