To alleviate the contradiction between bandwidth extension and manufacturability of dual-band FSS, the bandwidth extension technology based on stub loading is studied.

First, the main factors causing the above contradiction by conventional bandwidth extension methods are analyzed. Second, the influence of stub loading on the electromagnetic characteristics of FSS is studied, such as the reactance characteristics, shape, and quantity of stubs. Finally, the first/second transmission passbands of FSS are extended by stub loading on the grid/slots, respectively, and the mitigation effect of stub loading technology on the above contradiction is analyzed in detail.

Simulation results show that compared with the traditional bandwidth extension method, the stub loading technology can improve the dual-band bandwidth by 48.8% and 23.2% respectively under the same metal line width (0.1 mm), and the test results are in good agreement with the simulation results.

Stub loading can effectively alleviate the contradiction between multi-band bandwidth extension and manufacturability, providing theoretical guidance for engineering practice.

To overcome the limitations of conventional wave-absorbing structures, a novel broadband, low-profile multilayer composite absorber was designed.

The proposed design integrates square loop resistive film units to significantly broaden the operational bandwidth and incorporates miniaturized conductor units based on lumped inductance loading. Structural parameters were further optimized to achieve broadband, low-profile wave-absorption, effectively lowering the minimum operational frequency.

Simulation results show that the developed composite absorber achieves over 90% electromagnetic wave absorption across the frequency range of 3.22 to 14.63 GHz, with a relative bandwidth of 127.8% and a low profile height of just 0.068λ_L.

The operational mechanism of the absorber is analyzed using an equivalent circuit model, and potential improvements are discussed. This design offers valuable insights and a solid reference for the development of broadband, low-profile absorbers. Future work will focus on replacing lumped inductors with metal meander-line structures to reduce processing complexity and costs.