A Generalized Synthesis Technique for High-Order Ultrawideband Microwave Absorbers

A generalized synthesis technique for a new class of high-order ultrawideband microwave absorbers is presented in this article. First, a generalized circuit model of high-order ultrawideband microwave absorber is proposed based on the principle of a multistage impedance matching network, whose frequency response can be synthesized with Chebyshev polynomials of the first class over a wide frequency range. Following the synthesis procedure, all circuit parameters for arbitrary fractional bandwidth and minimum return loss in the absorption band can be accurately calculated. Subsequently, physical structures are realized by means of stacked printed circuit board pieces etched with slotlines and embedded resistors. The physical parameters of the slotlines are extracted with high precision under periodic boundary conditions. The fourth- and fifth-order absorbers are then designed, fabricated, and measured with distinct design specifications. The measured results correspond well with the simulated ones. Additionally, both absorber designs demonstrate good angular stability even when exposed to the 50° oblique incidence. Therefore, the proposed generalized circuit model and synthesis method are evidently validated and can provide an efficient and accurate solution to design this kind of high-order ultrawideband microwave absorbers. Furthermore, it provides a broader absorption band while utilizing the minimal number of resistors, making it highly practical for a wide range of applications.