A wide-angle reconfigurable reflectarray antenna (RRA) utilizing a miniaturized ring patch that can be efficiently controllable with a single bit is designed and experimentally verified. Based on the adoption of miniaturized radiating element and the elaborate study to optimize quantization efficiency considering reference phase and asymmetric phase difference, highly directive beam scanning is achieved in a wide ±60° range in both the $H$ - and $E$ - planes. Furthermore, the feeding structure to minimize focal diameter ratio (F/D) and maximize feeding efficiency such as illumination and spillover Efficiencies is studied, resulting in a low profile configuration with F/D=0.36. The fabricated RRA prototype was measured at 9.85 GHz (X-band) with the highest aperture efficiency of 28% and a 1 dB gain bandwidth of 530 MHz, respectively.

In this study, a broadband metasurface absorber composed of an optimal combination of copper tiles connected with four chip resistors is designed and experimentally verified. After fixing the locations of the chip resistors and setting their resistances to 100 $\mathsf{\Omega }$, the genetic algorithm (GA) is utilized to design the optimal copper tile pattern for broadband absorption. The optimal combination of the copper tiles is identified by determining the states of the square tile pairs between copper or air, depending on the one or zero states of the bit sequence created by GA, respectively. The full-wave simulation results of the optimized metasurface absorber confirmed a $-10$ dB reflectance bandwidth within the frequency range of 6.57 to 12.73 GHz for the normal incidence condition, with the fractional bandwidth being $63.83\%$. The accuracy of the metasurface absorber was verified through an experimental result that matched well with the full-wave simulated one.

An ultrawideband electromagnetic metamaterial absorber is proposed that consists of double-layer metapatterns optimally designed by the genetic algorithm and printed using carbon paste. By setting the sheet resistance of the intermediate carbon metapattern to a half of that of the top one, it is possible to find an optimal intermediate metapattern that reflects and absorbs the EM wave simultaneously. By adding an absorption resonance via a constructive interference at the top metapattern induced by the reflection from the intermediate one, an ultrawideband absorption can be achieved without increasing the number of layers. Moreover, it is found that the metapatterns support the surface plasmon polaritons which can supply an additional absorption resonance as well as boost the absorption in a broad bandwidth. Based on the simulation, the $$90\%$$90% absorption bandwidth is confirmed from 6.3 to 30.1 GHz of which the fractional bandwidth is 130.77 $$\%$$% for the normal incidence. The accuracy is verified via measurements well matched with the simulations. The proposed metamaterial absorber could not only break though the conventional concept that the number of layers should be increased to extend the bandwidth but also provide a powerful solution to realize a low-profile, lightweight, and low cost electromagnetic absorber.

A hybrid reflectarray antenna (RA) composed of passive and active unit cells that can steer a beam into two selected directions with high aperture efficiencies is designed and experimentally verified. The hybrid RA is implemented by a combination of one-bit active and passive unit cells, which enables the quantization of phase profiles of the reflection coefficients on the antenna surface to 120°. This combination can improve the quantization efficiency of the conventional one-bit reconfigurable RA quantized with 180°. A combination of the passive unit cells of which the phases of reflection coefficients are 180° is determined to be included simultaneously in two quantized phase profiles for two-direction beam steering. As a proof of concept, the hybrid RA is designed to steer the beam to the vertical angles θ of -18° and 18° on the E-plane. By comparing them with those of the one-bit RA, we confirmed that the aperture efficiencies are improved by 41.85% and 69.41% in simulations and by 37.19% and 60.19% in measurements for the vertical angles θ of -18° and 18°, respectively.

A design method for a broadband and wide-angle metamaterial absorber is proposed based on optimal tiling of rhombus carbon pixels on and implantation of metal cylinders inside an acrylic substrate for which the backside is blocked by the perfect conductor. First, an intermediate carbon metapattern is achieved via optimal tiling of rhombus carbon pixels based on the genetic algorithm (GA), which can minimize the reflectances of both of the transverse electric (TE) and transverse magnetic (TM) polarized electromagnetic (EM) waves for the incident angles $0^{\circ }$ and ${60}^{\circ }$ simultaneously. Then, copper cylinders are implanted inside the substrate to boost the absorptions of both of the TE and TM polarizations for the ${60}^{\circ }$ oblique incidences. To extend the absorption bandwidth, the design is finalized by evolving the intermediate metapattern using the GA. Based on the finalized carbon metapattern, the $90\%$ absorption bandwidth is confirmed in the frequency range 8.8 to 11.6 GHz, for which the fractional bandwidth is $27.5\%$ for both of the two polarizations with the incident angles from $0^{\circ }$ to ${60}^{\circ }$. The proposed method could open a way to design a broadband and wide-angle EM metamaterial absorber that can be applied to the edges of three-dimensional structures such as a regular tetrahedron or square pyramid that have interior angles of ${60}^{\circ }$ that cannot be covered by conventional square or rectangular metamaterial absorbers.

In this paper, a design strategy for a wide-angle metasurface absorber is proposed that evolves a configuration for broadband absorption that consists of four 100 Ω chip resistors and a combination of square copper tiles. To satisfy -10 dB reflectance at all incident angles up to 60° for both transverse electric (TE) and transverse magnetic (TM) polarizations, the copper tiles were recombined. To this end, a transformative genetic algorithm was applied, of which the figure of merit was converted from the original one by multiplying a scaling factor with the worst reflectance in the target band. The simulation results confirmed a -10 dB reflectance ranging from 10.8 to 11.21 GHz, with the fractional bandwidth being 3.73% for both TE and TM polarizations at incident angles ranging from 0° to 60°. The accuracy of the proposed design was verified by conducting measurements, which matched well with the simulated results.