Absorptive Frequency-Selective Transmission Structures Based on Hybrid FSS and Absorber

The replacement of lumped resistors with absorbing materials for absorptive frequency-selective transmission (AFST) structures enables a wider range of applications in low radar cross section (RCS) radomes. However, the transmission band within the absorption band for most absorbers is naturally nonexistent. It is shown that such a limitation can be overcome with the engineered frequency-selective surfaces (FSSs) and microwave absorbers to obtain a frequency response of absorption-transmission-absorption. In particular, a transmission window of low insertion loss within the absorption band is introduced by the integration of bandpass FSS and wideband absorber, while a bandstop FSS in the front minimizes the insertion loss in the passband. This design methodology is successfully demonstrated by two examples of AFST structures with single and dual polarizations.