Liquid Based Wideband and Switchable 3-D Frequency-Selective Rasorber

A switchable 3-D frequency selective rasorber (FSR) with wide absorption bands and without lumped components or commercial magnetic absorbers is presented. The absorption path is constructed by embedding a hybrid liquid microwave absorber inside a parallel plate waveguide to create an extra-wide absorption band. A reflection layer based on water is placed behind the FSR to realize the reconstruction from FSR to a band-notched absorber (BNA) by controlling the presence or absence of water. The liquid-based absorber is analyzed by a multimode dielectric resonant circuit, and the fundamental operating principle of the FSR is demonstrated with the help of an equivalent circuit model. A prototype is designed, fabricated, and measured and exhibits a passband at 5.10 GHz with a transmission bandwidth of 18.5% for less than 3 dB insertion loss and a fractional bandwidth of 146.8% with reflectivity less than -10 dB in the FSR mode. In the BNA mode, it has a minimum return loss of 0.72 dB and a good absorption band from 2.5 to 4.6 GHz and from 5.7 to 16.5 GHz. This switchable FSR may be used in an antenna system to decrease out-of-band reduce radar cross section while also functionally enabling switching between the radome and the antenna reflector.