A compact planar quad-element ultrawideband (UWB) antenna with a band-notch and low coupling for multiple-input multiple-output (MIMO) system is proposed in this paper. The antenna consists of four circular monopoles with modified defected ground plane and a periodic electromagnetic band gap (EBG) structures. The proposed EBG structures are modified from the traditional mushroom-like ones, comprised of patterns of grids on the top patch, the metallic ground plane, and several vias that connect the top and bottom plane. It is printed at the center of the dielectric substrate to lower electromagnetic coupling between the parallel elements. Besides, by etching four crescent ring-shaped resonant slots on the radiators, a sharp band-notched characteristic is achieved. From the experimental results, the −10 dB bandwidth of the antenna is extended covers from 3.0 to 16.2 GHz, with a sharp notched band at 4.6 GHz. And the isolation is greater than 17.5 dB between its elements, with a peak gain of 8.4 dB and a peak efficiency of 91.2%. Moreover, it has a compact size of 0.6λ×0.6λ×0.016λ at 3 GHz and could be a good candidate for portable devices.

Recently, by introducing locally resonant scatterers with spherical shape proposed in phononic crystals into design of underwater sound absorption materials, the low-frequency underwater sound absorption phenomenon induced by the localized resonances is observed. To reveal this absorption mechanism, the effect of the locally resonant mode on underwater sound absorption should be studied. In this paper, the finite element method, which is testified efficiently by comparing the calculation results with those of the layer multiple scattering method, is introduced to investigate the dynamic modes and the corresponding sound absorption of localized resonance. The relationship between the resonance modes described with the displacement contours of one unit cell and the corresponding absorption spectra is discussed in detail, which shows that the localized resonance leads to the absorption peak, and the mode conversion from longitudinal to transverse waves at the second absorption peak is more efficient than that at the first one. Finally, to show the modeling capability of FEM and investigate shape effects of locally resonant scatterers on underwater sound absorption, the absorption properties of viscoelastic materials containing locally resonant scatterers with ellipsoidal shape are discussed.

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A novel ultra‐wideband (UWB) antenna with chessboard‐shaped patch is successfully designed by employing planar patterned metamaterial in this paper. The metamaterial antenna has two layers, a novel chessboard‐shaped patch on the top layer and a planar metallic ground carved grid patterned gaps on the bottom layer. This novel antenna has a fractional impedance bandwidth of 71%, which is far more than that of a corresponding conventional patch antenna. Its radiation efficiency is higher than 88% within its operating frequency range 3.5∼7.9GHz and a maximum radiation efficiency of 96% has been achieved. Its gain is varied from 2.7 to 6.9dBi within its operating bandwidth. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:3008–3012, 2016

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that of the nonself-aligned RTD. The calculated f C of the self-aligned RTD is increased by about 13.6% compared with that of the nonself-aligned RTD. The results show that the fabricated self-aligned RTD with the SiN X sidewall process improves the RF performance by reducing the spacing (d) resulting in lower R S due to reduced R SEMI . By using a scaled-down device technology with an electron beam lithography, the high-speed characteristics of the self-aligned RTDs will be improved. | C ONCL US I ONA self-aligned RTD using a SiN x sidewall process has been fabricated and characterized. The dry etching process has been developed for the self-aligned RTD with 5 lm 2 emitter size to obtain the highly anisotropic mesa profile. The fabricated RTD showed the PVCR of 13.1 with a peak voltage (V P ) of 0.348 V. The measured peak currents and peak voltages were almost constant in the temperature range between 25 and 1258C. The self-aligned RTD showed the R S reduction of 27% compared with the nonself-aligned RTD by reducing the spacing between emitter mesa and collector metal. The results achieved in this work indicate that the self-aligned RTD with the SiN X sidewall will offer a viable option for the future high-speed microwave applications. ORCIDKiwon Lee http://orcid.org/ AbstractIn this work, a novel very wideband 4-element monopole based multiple-input multiple-output (MIMO) antenna system with single connected antenna array (CAA) is presented. The CAA is based on a single slot which is etched on the ground plane. A 2 3 1 power divider/ combiner is used to excite the slot to act as a CAA. The