Metamaterial absorbers have attracted much attention due to their unique ability to achieve nearly perfect absorption in compact structures. Most of the reported metamaterial absorbers exhibit only one absorption band in a specific frequency range, but absorbers with two or more absorption bands in the visible and near-infrared regions are desired in many applications. Here, we propose and demonstrate a dual-band metamaterial absorber comprising an aluminum film, a silica spacer, and a periodic array of aluminum nanodiscs. The two absorption bands in the visible and near-infrared range are, respectively, attributed to the excitation of a propagating surface plasmon polariton and a localized magnetic polariton in the proposed nanostructure. Large area and high coverage samples of the designed structure were fabricated using a simple and cost-effective colloidal lithography nanofabrication method. We show that the positions of the absorption bands can be separately adjusted by changing the diameter or the lattice constant of the aluminum nanodiscs on the top of the metamaterial absorbers. Our design of compact and efficient absorbers would find great utility in a variety of applications including filters, sensors, solar cells, thermal emitters, and imaging devices.
Abstract-A novel feed network based on the microstrip/slotline transition is proposed in this paper. This feed network not only has ultra-wide impedance bandwidth but also can improve space utilization and make the design of antenna array easier. Then an ultra-wideband (UWB) antenna array with four elements fed by the network is designed. The antenna array is simulated, manufactured and measured. The results show that the impedance bandwidth with return loss under −10 dB is 88.76%, from 2.35 GHz to 6.1 GHz. Within the impedance bandwidth, the radiation performance is satisfactory, and the gain of the array is 2.1-7.1 dB, higher than that of the element. The cross-polarization level of the array is lower than −20 dB, just as the element. A reasonable agreement of results is achieved between simulation and measurement.
A miniaturized triple-band branch-line coupler based on the simplified dual-composite right/left-handed transmission line (S-D-CRLH-TL) is proposed in this paper. The electromagnetic characteristics of S-D-CRLH-TL are analyzed by the simulator and equivalent circuit model, and the results prove that there are three frequency points with phase of −90-degree in the passbands; this characteristic can be used to design triple-band quadrature microwave components. The proposed branch-line coupler is fabricated and measured, the measured and simulated results are in good agreement with each other, showing that the triple-band operating at 3.06 GHz, 4.00 GHz and 5.54 GHz, the useful bandwidths are 2.97 GHz-3.16 GHz, 3.82 GHz-4.12 GHz and 5.48 GHz-5.67 GHz. In addition, compared with the conventional branch-line coupler, the whole size of the proposed one is 17 mm×14.4 mm (0.173λ×0.147λ) (λ is the wavelength in low frequency), it realizes a 73% size reduction. Moreover, compared with the triple-band branch-line coupler based on the double-Lorentz transmission line metamaterial, the proposed branch-line coupler is more effective in the situation, which is sensitive to phase-changing, as the sign of phase difference in the two outputs at the three frequency points keeps the same.
A novel compact electromagnetic bandgap (EBG) structure consisting of two turns complementary spiral resonator (CSR) and conventional mushroom EBG (CM-EBG) structure is introduced to suppress the mutual coupling in antenna arrays for multiple-input and multiple-output (MIMO) applications. Eigenmode calculation is used to investigate the proposed CSR-loaded mushroomtype EBG (MT-EBG), which proved to exhibit bandgap property and a miniaturization of 48.9% is realized compared with the CM-EBG. By inserting the proposed EBG structure between two E-plane coupled microstrip antennas, a mutual coupling reduction of 8.13 dB has been achieved numerically and experimentally. Moreover, the EBG-loaded antenna has better far-field radiation patterns compared with the reference antenna. Thus, this novel EBG structure with advantages of compactness and high decoupling efficiency opens an avenue to new types of antennas with super performances.
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