Ultrathin 3-D Frequency Selective Rasorber With Wide Absorption Bands

A novel ultrathin 3-D frequency-selective rasorber (FSR) with wide lower and upper absorption bands is presented. The wide absorption band is achieved by using a commercial ferrite absorber and the ultrathin profile is realized using a slow wave structure. The ferrite absorber is very thin and operates over a wide frequency band due to its strong magnetic loss. The attractive low insertion loss feature is obtained through bypassing the ferrite absorber with a series L-C circuit at the passband frequency. An equivalent circuit model is proposed to analyze the physical mechanism of the proposed 3-D FSR and to formulate the design equations. A prototype of the proposed 3-D FSR is fabricated and measured. Tested results show a bandwidth (BW) of 26.6% for the transmission band with insertion loss less than 3 dB and a fractional bandwidth of 163.6% for reflection coefficient less than -10 dB can be obtained. A key feature of the proposed FSR is that its thickness is only 0.086λ
_c
, where λ
_c
is the free-space wavelength at the center frequency of the passband. Moreover, simulated results show that the proposed structure exhibits stable frequency responses under oblique incidence up to 45°.