The progress of technology in consumer electronics demand an antenna having a compact size, high gain and bandwidth, and multiple antennas at transmitter and receiver to enhance the channel capacity. Over the last decade, numerous techniques are proposed to improve the performance of the antenna. One such technique is the use of metamaterials (MTMs) in antenna design. MTMs are artificial structures to provide unique electromagnetic properties that are not available in natural materials. The unique properties of these materials allow the design of high-performance antennas, filters, and microwave devices which cannot be obtained using traditional antennas. Loading antenna with the one, two, and three-dimensional MTM structures comprised of a periodic subwavelength unit cell exhibits RLC resonant structures and allows to manipulate electromagnetic waves in the antenna system. These structures offer low resonant frequency compared to the antenna resonant frequency resulting in antenna miniaturization and manipulation of electromagnetic waves helps in enhancing the gain and bandwidth, and achieving circular polarization (CP) of an antenna system. Also, metamaterial loading enhances isolation between the antenna elements in the multiple-input-multiple output (MIMO) system by suppressing the surface waves. In this paper, the electromagnetics of MTM with analytical expressions and its application in antenna design are discussed in detail. The MTM-based antennas are classified into MTM loading, MTM inspired antenna, metasurface loading, and composite right/left hand (CRLH) based antennas. The recent development in MTM inspired antenna and its application in antenna miniaturization, enhancing gain and bandwidth, achieving CP and mutual coupling suppression in MIMO antenna systems are discussed to make it useful for further research.

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Electromagnetic Metamaterials: A New Paradigm of Antenna Design

This paper presents a design method of wideband Fabry–Perot resonator antennas (FPRAs) with two layers of electrically thin dielectric superstrates. The bandwidth enhancement mainly benefits from the superstrate structure with reflection phase increasing with frequency, which is used as a partially reflective surface. The proposed method is validated by a design example in ${X}$ -band. Experimental results of the FPRA prototype demonstrate that the 3-dB gain bandwidth ranges from 8.5 to 11.2 GHz (relatively 28%) with a peak gain of 14 dBi and coincides with the impedance band for ${S} _{11}\leqslant -10$ dB. Compared with the existing methods of gain bandwidth enhancement, the one presented in this paper does not need dielectric substrates with a large or fixed electrical thickness, improving cost performance and design flexibility.

Wideband Fabry-Perot Resonator Antenna With Electrically Thin Dielectric Superstrates

Directive pencil beams scannable in both elevation and azimuth are obtained through a planar phased array placed inside a Fabry–Perot cavity. The key element of the proposed approach is the exploitation of a conical element pattern (EP) with high directivity in elevation, obtained through the excitation of a dominant, weakly attenuated cylindrical TM leaky wave of azimuthal order $n = 0$ by means of a simple coaxial probe. Then, a highly reduced number $N$ of such sources are arranged to form a phased array radiating directive pencil beams. Beam-angle reconfigurability with continuous scanning both in azimuth and elevation inside a wide solid angular range is achieved by varying the array phasing and the operating frequency. An investigation on the features of truncated cylindrical leaky waves is first developed to properly characterize the EP. Then, conventional array theory is exploited to calculate the pattern of the entire array. The radiation efficiency is also evaluated accounting for the spurious surface wave related to the undesired excitation of the quasi-TEM mode. The proposed array design provides a simple and inexpensive innovative solution for obtaining a high-gain pencil beam continuously scanning in the 3-D space without suffering gain losses. In the presented implementation, the elevation angular scan, which is generally constrained by the wideband capability of the feeding system, by the requirements on the sidelobe level, and by the cutoff of the relevant leaky mode, ranges from about 21° to about 68°. Possible applications are envisaged for the next generation of wireless power transfer devices, for advanced radar and surveillance systems, earth observation, as well as for ceiling-mounted indoor localization and tracking.

2-D Beam Scanning With Cylindrical-Leaky-Wave-Enhanced Phased Arrays

Graphene oxide is an emerging nanomaterial with diverse applications for energy storage, conversation (electrodes) and industrial wastewater treatment (adsorbent and photocatalysts) because of their outstanding electrical, thermal and chemical properties. In view of this background, this review paper examines the properties, preparation methods and characterization techniques for graphene oxide (GO) nanostructured materials. A brief strategy for improving GO efficiency such as doping/co-doping GO with selected heterogeneous semiconductor metal oxides was provided. The immobilisation of GO with a high bandgap material resulting to the shifting of absorption threshold to the visible region and enhancement of photoactivity performance were also discussed. The application of GO based nanomaterial in Fenton like reaction, ozonation , photocatalysis , photo-Fenton, photoelectrocatalysis and combination of photocatalysis and photon-Fenton for water treatment applications were provided. The presence of graphene oxide nanostructured materials in composite material enhanced the overall performance in their respective applications. Finally, the review provides insight into future perspectives and improvements especially the scaling up of graphene oxide based nanocomposites based technology for industrial wastewater treatment. 

A critical review on graphene oxide nanostructured material: Properties, Synthesis, characterization and application in water and wastewater treatment

Over the past few years, there has been a huge demand to design a simple printed antenna for high-speed multimedia communication with low cost, compact size, wide band, and low copolarization (CP) to cross-polarization (XP) isolation levels. In this letter, a simple and completely planar air-gap-loaded rectangular microstrip antenna integrated with single shorting post and defected ground structures has been thoroughly investigated to obtain wide bandwidth of 58.72% (8.3–15.2 GHz) at X - and Ku -band. Besides exhibiting good broadside patterns and desirable gain (>5 dBi), good CP-to-XP isolation levels (16 dB) are also achieved. Furthermore, the proposed antenna has a low profile of 0.083 λ0.

DGS-Integrated Air-Loaded Wideband Microstrip Antenna for X - and Ku -Band

A new wideband and enhanced gain Fabry–Perot cavity antenna is presented in this letter. The Fabry–Perot cavity is established between a single-layer metamaterial-based partially reflective surface (PRS) and a simple feeding slot antenna. The unit cell of the PRS consists of printed and etched square rings on both sides of the superstrate. A 6 × 6 array of the unit cells is optimized to produce a positive reflection phase gradient required for the gain enhancement. Simulated results of the designed Ku-band antenna demonstrate an impedance bandwidth of 13.1–15.3 GHz (15.5%) with a gain enhancement up to 8.2 dB (i.e., 150% gain increase above the feeding antenna) and a 3 dB radiation bandwidth of 18.7%. Experimentally observed reflection and radiation responses of the fabricated prototype validate the simulated results.

Directive Wideband Cavity Antenna With Single-Layer Meta-Superstrate

Incorporating phased array technique to scan the main beam of a Fabry-Perot cavity (FPC) antenna produces sidelobes proportional to the scan angle. An alternative dielectric-ferrite superstrate-based scan mechanism with controlled sidelobe level is presented in this letter. A beam scan of 24 °
 is demonstrated by axially magnetizing the ferrite part of the superstrate with ΔH = 0.25 T. Stepped dielectric part of the superstrate is optimized to reduce the sidelobe level of the FPC antenna by 4.49 dB. The fabricated antenna is tested to verify the simulated radiation patterns and reflection responses. The requirement of magnetic biasing can be considerably reduced using LTCC technology, where biasing coils are embedded within the ferrite superstrate.

Superstrate-Based Beam Scanning of a Fabry–Perot Cavity Antenna

Microwave radiations effect on electrical and mechanical properties of poly (vinyl alcohol) and PVA/graphene nanocomposites

Axially magnetized ferrite loaded microstrip patch antenna (MPA) with tunable beam scanning properties is presented. Ferrite cylinders are optimally positioned within the near field region of the patch to introduce phase tapers needed for beam scanning. The interaction between the radiated EM wave and the gyrotropic properties of ferrites is controlled by varying the magnetizing fields. A beam scan of ° is achieved for a DC biasing range of 0–0.19 T. Simulated antenna properties are verified using experimental results. Recent LTCC technology allows the biasing coils to be embedded within the ferrite material to considerably reduce the required external magnetizing field.

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Beam Scanning Properties of a Ferrite Loaded Microstrip Patch Antenna

The ferrite-loaded, Fabry-Perot Cavity antenna uses a novel superstrate based beam scanning/shaping mechanism by optimally placing three magnetized ferrite cylinders within the cavity. Beam scan in a certain direction required oppositely located ferrite cylinder to be axially biased using externally controlled DC magnetizing field. The FPC utilizes a composite dielectric superstrate to inversely relate the mainlobe-to-sidelobe ratio with scan-angle, which demonstrates larger reduction in side lobe level with increases angle of beam scan. The designed 10 GHz ferrite-loaded FPC antenna has dimensions of 6.4 cm×2 cm×1.6 cm. It achieves a −10 dB impedance bandwidth of 525 MHz, directivity of 11.04 dB and a broadside beam steering range of ±12° for 200 kA/m (0.25 T) changes in the externally applied axial magnetizing field.

Sheikh Sharif Iqbal Mitu

Papers

Directive Wideband Cavity Antenna With Single-Layer Meta-Superstrate

Superstrate-Based Beam Scanning of a Fabry–Perot Cavity Antenna

Microwave radiations effect on electrical and mechanical properties of poly (vinyl alcohol) and PVA/graphene nanocomposites

Beam Scanning Properties of a Ferrite Loaded Microstrip Patch Antenna

Ferrite-loaded, Fabry-Perot cavity antenna