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Different methods to increase the bandwidth of a microstrip antenna, such as use of an air‐gap in‐between stacked resonators and the ground plane and planar multiresonators, are combined to achieve broad bandwidth with increased gain. A configuration with two gap‐coupled circular microstrip antennas on the top dielectric layer stacked with one coaxial‐fed circular patch on the bottom layer and an air‐gap in‐between two layers and the ground plane yield a bandwidth of 1093 MHz (47%) with a gain of 9.54 dB at the S‐band frequency of 2.325 GHz. Also, dual‐band response with broadside radiation and improved gain at both frequencies is achieved by suitably changing parameters of this configuration. Parametric studies of this configuration on dielectric substrate for both broadband and dual‐band operation are presented in this paper. The experiments are performed on broadband and dual‐band configurations, which are in agreement with the theoretical results. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 489–494, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21208

This paper reports a novel graphene metasurface exhibiting near-unity absorption over a wide bandwidth of 9.74 THz ranging from 2.06 to 11.80 THz with a fractional bandwidth of 140.86% with respect to the center frequency of 6.93 THz within the terahertz gap of the electromagnetic spectrum. The proposed structure consists of two layers of graphene separated by silicon dioxide (SiO 2). On the top of SiO 2 , a modified fractal-shaped 1 nm thick graphene pattern is deposited while a square-shaped graphene pattern of identical thickness completely covers the backside of the SiO 2 substrate. The absorber was found to be polarization independent under the normal incidence of the approaching electromagnetic wave (EM) toward the top layer of the structure due to its 4-fold structural symmetry. The designed structure offers stable absorption up to 60 incident angle under TE polarization and 40 incident angle under TM polarization. The structure is~λ/55.9 thin and maintains periodicity of~λ/21.7; thereby validating the effective homogeneity condition in the sub-wavelength domain. This graphene-based absorber can find several applications including, sensors, detectors, spatial light modulators, and in spectroscopic detectors, and so forth, in the "Terahertz Gap" for next-generation 5G communication system and beyond.

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