Miniaturization of frequency-selective rasorber based on 2.5-D knitted structure

Knitted structure based on through-silicon vias is utilized to realize the miniaturization of frequency-selective rasorber (FSR). According to equivalent circuit model analysis, additional inductance and capacitance introduced by an array of metal vias are considered, which is combined with lossy cross-frame and lossless double square-loop structure to realize the function of FSR. Through full wave simulation, the proposed 2.5-D FSR demonstrates one passband between two absorption bands. The simulated results indicate a significant size reduction with P = 0.15 lambda(L), where lambda(L) is the free-space wavelength at the lowest frequency of -10 dB reflection. Moreover, an insertion loss of 0.49 dB can be observed at 3.99 GHz, the fractional bandwidth for reflection coefficients less than -10 dB is 100%, and the thickness of the whole structure is 0.138 lambda(L), respectively. In addition, the frequency response of this miniaturized FSR is stable for incident angle up to 40 degrees and both linear polarizations. After then, the prototype of this 2.5-D FSR is fabricated and measured, which shows reasonable agreement with simulated results.