The present work reports a simple, inexpensive method for synthesis of calcium hydroxide [Ca(OH) 2 ] nanoparticles (CHNPs). The method involves chemical precipitation (CP) in aqueous medium at room temperature. Calcium nitrate dihydrate [Ca (NO 3 ) 2 .2H 2 O] and sodium hydroxide were used as precursors. The CHNPs were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Rietveld analysis, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), BET surface area evaluation as well as particle size distribution analysis techniques. The results confirmed the synthesis of CHNPs as the major phase. The CHNPs exhibited an average size of about 350 nm. In addition, some calcite phase formed due to the inevitable carbonation process. A very minor amount of aragonite phase was also present. A schematically developed new qualitative model is proposed to explain the genesis and subsequent evolution of the various phases at the nanoscale. The model helps to identify the rate-controlling step. It also highlights the implication of reaction kinetics control in synthesis of predesigned nanophase assembly.

Here, an ultra‐wide stop‐band single‐layer frequency‐selective surface (FSS) with high‐incidence angle independence has been proposed to enhance the gain of an ultra‐wideband (UWB) monopole antenna. The unit cell (0.2λ × 0.2λ) of the proposed FSS consists of four asymmetric rectangular patches with circular slots embedded in it. This concept of four slotted patches is conceived to achieve ultra‐wide stop‐band characteristic over 4.7–14.9 GHz. An equivalent lumped circuit model for the FSS is proposed to provide insight into the working nature of the FSS. A UWB monopole antenna is also designed and integrated with the proposed FSS. Ultra‐wide stop‐band single‐layer FSS converts the omnidirectional pattern of the monopole antenna into a unidirectional one and thereby registers a significant increase in its gain by 4.5 dBi. The design concept has been discussed and experimentally verified using simulated and measured results.

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