Wideband 3-D Microwave Absorber With 75 $^{\circ}$ Angular Stability Using Hybrid Synthesizable Element Arrangement

In this article, a wideband 3-D microwave absorber with 75
$^{\circ}$
angular stability is proposed using a hybrid synthesizable element arrangement. First, the operating principle of the synthesizable absorber element is investigated, where the filtering energy conversion function is synthesized and designed based on the established universal equivalent transmission line (TL) model. After applying different synthesized angles (SAs), the key finding is that absorption ratios (ARs) under large and small SAs can be compensated by each other, which is able to realize the stable and efficient absorption in a larger angular range. Combining two 45
$^{\circ}$
SAs (for small incident angles) and one 60
$^{\circ}$
SA (for large incident angles) in one absorber element, the angular stability is significantly improved to 75
$^{\circ}$
by adopting the hybrid element (HE) arrangement. Moreover, a profile-reduced absorber design is further accomplished by employing the folded structure. Finally, a prototype is structurally designed and practically implemented. Measurements agree well with synthesized and simulated results, which successfully proves our presented design concept in this article. Under specific incident angles of 0
$^{\circ}$
, 45
$^{\circ}$
, 60
$^{\circ}$
, and 75
$^{\circ}$
, the measured average ARs in the desired 122% bandwidth (from 3.9 to 16.1 GHz) are 77.3%, 91.4%, 90.2%, and 82.4%, respectively. Furthermore, the proposed absorber possesses a manufacture-friendly structure with only one piece of resistive layer. Therefore, such analysis method and structural design of microwave absorbers are promisingly believed as potential candidates for wideband and wide-angle absorption coverage.