Heteroatom doping engineering is desirable in tuning crystal structures and electrical properties, which is considered an opportunity to further develop microwave absorption materials. However, the competition mechanism and priority among doped atoms have not been revealed, which are insufficient to guide the most reasonable dielectric coupling model and design highperformance absorbers. In this work, based on in situ N and O, ex situ S is introduced through external thermal driving, leading to fierce competition among anions. Specifically, S atoms replace pyrrole N, drive out lattice O, and create O vacancies, bringing more extensive local charge redistribution and stronger electron interaction, thus activating the defect-induced polarization (3-6 times higher than conduction loss) in the middle/high-frequency region. Therefore, the effective absorption bandwidth (EAB) of 9.03 GHz and the minimum reflection loss (RL min ) of −64.05 dB at a filling rate of 10 wt.% are obtained, which improves the record of carbon absorbers as reported. Through macro-designs, i.e., multi-layer gradient metamaterial, or utilizing other advantages, e.g., cost-effective, stable chemical properties and wideangle absorption, porous carbon may possess a great application prospect in the naval field.

This article presented a broadband low-profile monopole antenna that was equipped with coplanar waveguide (CPW), substrate integrated waveguide (SIW), and slots based on characteristic mode theory (CMT). Compared with the traditional antenna design method, the antenna design method based on CMT can design the antenna more effectively. A prototype of the proposed antenna with an overall size of 0.98 λ 0 Â 0.98 λ 0 Â 0.027 λ 0 (λ 0 is the free-space wavelength at the X-band of 8.2 GHz center frequency) was fabricated and measured. The measurement results showed that the prototype had a impedance bandwidth of 3.2 GHz (6.8-10 GHz), a relative bandwidth of 38.1%, the maximum gain of 4.1 dBi at 9.5 GHz, and the maximum radiation efficiency of 92%. Besides, it was found that the prototype almost achieved symmetrical radiation in E-plane and omnidirectional radiation in H-plane. Its operating frequency band covered that of broadcast band (7.1-7.3 GHz), the water mobile band (8.1-8.815 GHz), and the aviation mobile band (8.815 -9.04 GHz).

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