Triple band single layer microwave absorber based on closed loop resonator structures with high stability under oblique incidence

Abstract

A novel triple-band microwave absorber design which is independent of polarization with extremely high stability under oblique incidence is described in this paper. The proposed absorber structure's unit cell architecture contains three closed loop microstrip resonator components with rotational symmetry. The suggested design engenders three reflection nulls at 2.4 GHz (WiMAX), 5.5 GHz (WLAN) and 7.51 GHz (downlink satellite communication frequencies in the X-band). These gives rise to triple absorption peaks with near-unity (almost 100 %) absorptivity at the mentioned frequencies. The absorber design is fully immune to polarization for both TE and TM modes of propagation. Furthermore, the structure offers very high stability under oblique incidence for both TE and TM modes where beyond 90 % absorptivity is obtained up to 520 incident angles and beyond 80 % absorptivity is achieved up to 750 incident angles. The unit cell size is 0.12λ0 × 0.12λ0, where λ0 is the wavelength corresponding to the lowest absorption frequency. The advantage of the proposed structure over other reported absorbers is assessed by its superiority in terms of multiband functionality, full polarization insensitivity, stability under oblique incidence and compactness. A prototype of the proposed absorber was fabricated and the measured results agree closely with the simulation results.