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

The wide bandwidth pyramidal microwave absorbing materials are required for use in antenna and electromagnetic compatibility (EMC) anechoic chambers. The main design criteria are to maximize the frequency range that can be utilized in the test volume available. Ferrite tile absorbers have good absorbing performance below 1 GHz with a few millimeters in thickness. For the attainment of microwave attenuation above 1 GHz, pyramidal ohmic absorbers (which are in the form of carbon-embedded urethane foam) are conventionally used. For this pyramidal absorber, however, the overall thickness is too big (in general, above 30 cm) restricts its use in small or semi-anechoic chambers.The purpose of this study is to design the pyramidal absorbers with wide bandwidth and reduced thickness by using lossy ferrite materials . Three types of ferrite materials (NiZn spinel ferrite, Co₂Z hexaferrite, and RuCoM hexaferrite) with different frequency dispersion of magnetic loss were used as the absorbent fillers in polymer matrix .