In this paper, the analysis of an UWB monopole antenna using the Theory of Characteristic Modes is presented. It starts from the modal study of an asymmetric dipole (structure 1), and then complements and compares it with a broadband monopole (structure 2), aiming to understand the operation principle of the proposed antenna. To achieve this, the electromagnetic properties of the structures are analyzed through the generation of its characteristic angles, modal radiation patterns, characteristic currents, and the power contribution percentage of each mode to the total radiated power, providing a vision on how the superposition of individual characteristic modes enables UWB operation. The prototype model is fabricated, and the measured results agree very well with the full-wave simulations results. The proposed prototype has a very low profile and operates in the frequency band from 2.8 GHz to exceed 10 GHz for a reflection coefficient S11 less than -10dB.

Building on our earlier work on graphene oxide (GO)-impregnated clinoptilolite for methylene blue (MB) removal, this study directly compares GO-modified zeolite (GOZ) with an ascorbic-acid-reduced analogue (rGOZ) prepared on the same clinoptilolite matrix by liquid-phase impregnation and evaluated under identical batch conditions. Spectroscopic/microscopic, elemental (CHNS) and textural analyses (UV–Vis, FT-IR, SEM/EDS, N ₂ sorptiometry and thermogravimetry) confirm successful attachment of the carbon phases (~ 9% graphene loading) and reveal distinct surface chemistries: GOZ retains abundant oxygenated groups, whereas rGOZ is more graphitic and both composites exhibit partial pore blocking. Relative to pristine clinoptilolite (q ~ 35 mg g ⁻¹ at 298 K), the maximum MB uptake (Langmuir) increases to ~ 157 mg g ⁻¹ for GOZ and ~ 123 mg g ⁻¹ for rGOZ, demonstrating a substantial enhancement upon carbon-phase incorporation. Adsorption is favored near neutral pH, follows pseudo-second-order kinetics for both composites, and shows endothermic, entropy-driven, spontaneous behavior over 298–333 K. Equilibrium data indicate more heterogeneous/pore-filling contributions for GOZ and a more monolayer-like, π–π-assisted uptake for rGOZ, consistent with their different functional-group densities. Regeneration by 0.1 N HCl washing over five cycles shows higher durability of GOZ, with MB removal decreasing from ~ 98% (cycle 1) to ~ 84% (cycle 5), compared with rGOZ decreasing from ~ 93 to ~ 71%. Overall, these results quantify how the oxidation state of the graphene phase governs MB uptake and reuse performance in clinoptilolite-based hybrid adsorbents. Graphical abstract

This paper presents a frequency reconfigurable antenna, based on four PIN diodes implemented on one of each corner of a rectangular patch antenna. A combination of three switching configurations of the PIN diodes provides a current path modification, and consequently a variation on the operating frequencies. Simulated results are presented based on two approaches, the ideal case using a metal portion and the schematic case employing the equivalent circuit of the PIN diode. The proposed antenna is suitable for 5 GHz U-NII band. Results are obtained by using CST-MW simulator.

This paper presents a low profile unidirectional UWB cavity backed antenna analyzed using The Theory of Characteristics Modes (TCM). The main goal of this work is to design a low profile UWB antenna with a very stable and unidirectional radiation pattern. The proposed design is based on exciting the fundamental mode of a cavity structure composed of a metallic ring, a circular waveguide and two circular feeds. The feeding structure used to excite this mode is symmetric and is implemented with a capacitively-coupled dual-feed circular aperture. In addition, an analysis of the operation of the structure is performed, according to the TCM. The -10 dB bandwidth obtained is 89.71% (3.48 GHz to 9.15 GHz), with unidirectional radiation patterns. An antenna with this bandwidth, as well as unidirectional and stable radiation pattern features can be used in many applications.