A technique of interdigital shifted opposite layers (SOLs) to design the miniaturized ultra-thin metamaterial absorber (MA) is proposed in this article. To meet the demanding requirements of small dimensions at low frequency, SOLs are first employed in MAs to achieve superior miniaturization. They consist of two identical layers printed on both sides of a thin substrate with relative lateral displacement. Compared with previously published MAs, the displacement substantially increases the equivalent capacitance of the unit cell, thus leading to a lower resonant frequency. To further miniaturize the unit cell, an ultra-thin MA using interdigital SOLs is optimized with a small cell size of 0.036 λ0 × 0.036 λ0 and a low profile of 0.0053 λ0 (where λ0 corresponds to the free-space wavelength at a resonant frequency), exhibiting perfect absorption at 0.868 GHz. The equivalent circuit model shows that the dramatically increased equivalent capacitance and inductance down-shift the resonant frequency. Meanwhile, the current flow and field distribution are investigated to explain the absorption mechanism. Finally, to validate the design concept, the fabricated prototype of the proposed MA has been measured and compared with the simulation result. The measured and simulated results show good agreement.

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A novel mapping approach is proposed to relax the manufacturing tolerances of FSS‐based microwave absorbers (MAs). A general reverse formulation for multilayered FSS‐based MAs is first deduced, and then the design objective of reflection coefficient |Γ| is mapped to a solution region of FSS's surface impedance Zs. Together with HFSS, the base FSS configuration with maximum acceptable tolerance can be identified through optimization, where target parameters have the widest variations with Zs located in the solution regions. Compared with the conventional overdesign‐before‐verification strategy for tolerances, the proposed approach explicitly visualizes the design solutions and achieves the maximum acceptable tolerances without an empirical trial‐and‐error process. Finally, aiming at the standard manufacturing tolerance of sheet resistance R□, the proposed approach is experimentally verified by a wideband absorber designed with a maximum R□ tolerance of ±21.4%. The measured result shows that the structure can easily fulfill the objective under the standard ±20% R□ tolerance.

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This article presents a novel low‐profile planar microstrip transmitarray antenna with high efficiency. First, a double‐layer planar microstrip transmitarray element is designed. The element consists of only one single substrate layer and two metallic layers, and two same modified Jerusalem cross‐shaped patches are etched on two sides of the substrate. These two patch layers are also connected by four specially designed metallic vias. The transmitarray element achieves more than 360° transmission phases with more than −3‐dB transmission amplitudes. Then, a low‐profile X‐band 145‐element circular‐aperture microstrip transmitarray antenna with the standard pyramidal horn feed is designed, fabricated and measured. The thickness of the microstrip transmitarray is 0.14λ0, where λ0 is the wavelength corresponding to the center frequency 10.6 GHz. Measured results indicate that gain of the transmitarray antenna at the center frequency 10.6 GHz is 25.4 dBi, its radiation efficiency is 53.8%, and its 1‐dB gain bandwidth is 7.8%.