Whale Optimization Algorithm (WOA) is an optimization algorithm developed by Mirjalili and Lewis in 2016. An overview of WOA is described in this paper, rooted from the bubble-net hunting strategy, besides an overview of WOA applications that are used to solve optimization problems in various categories. The best solution has been determined to make something as functional and effective as possible through the optimization process by minimizing or maximizing the parameters involved in the problems. Research and engineering attention have been paid to Meta-heuristics for purposes of decision-making given the growing complexity of models and the needs for quick decision making in the engineering. An updated review of research of WOA is provided in this paper for hybridization, improved, and variants. The categories included in the reviews are Engineering, Clustering, Classification, Robot Path, Image Processing, Networks, Task Scheduling, and other engineering applications. According to the reviewed literature, WOA is mostly used in the engineering area to solve optimization problems. Providing an overview and summarizing the review of WOA applications are the aims of this paper.

A comprehensive survey: Whale Optimization Algorithm and its applications

Modern Antenna Design

Metamaterials, artificial structures with unexpected properties, only function over a limited spectral window. Scientists have recently determined that the technique of combining a metallic metamaterial with a dielectric interlayer creates a device that modulates light over a wide range of frequencies.

https://absimage.aps.org/image/MAR15/MWS_MAR15-2014-001183.pdf

Controlling the Polarization State of Light with a Dispersion-Free Metastructure

A wideband reflective polarization converter based on metasurface is proposed in this letter. This converter can transform a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in a lower band, and a circularly polarized (CP) reflection wave in a higher band. The unit cell of this converter is comprised of two meander lines and one cut wire printed on a dielectric substrate, backed with metallic ground sheet. The simulation results show that the y / x -polarized incident EM wave can be converted to the x/y -polarized reflected wave over a fractional bandwidth of 59.6% from 6.53 to 12.07 GHz with a polarization conversion ratio over 0.88. Besides, the y / x -polarized incident EM wave is converted to a CP reflected wave from 13.70 to 15.60 GHz (a fractional bandwidth of 13.0%). To verify the polarization conversion performance, a sample consisting of 30 × 30 unit cells is fabricated and measured. The experimental and simulation results obtained are in a reasonable agreement, which verifies the properties of the design.

Wideband Metasurface-Based Reflective Polarization Converter for Linear-to-Linear and Linear-to-Circular Polarization Conversion

This paper presents a metasurface-based single-layer low-profile circularly polarized (CP) antenna with the wideband operation and its multiple-input multiple-output (MIMO) configuration for fifth-generation (5G) communication systems. The antenna consists of a truncated corner patch and a metasurface (MS) of a 2 × 2 periodic square metallic plates. The distinguishing feature of this design is that all the radiating elements (radiator and MS) are printed on the single-layer of the dielectric substrate, which ensures the low-profile and low-cost features of the antenna while maintaining high gain and wideband characteristics. The wideband CP radiations are realized by exploiting surface-waves along the MS and its radiation mechanism is explained in detail. The single-layer antenna geometry has an overall compact size of 1.0λ
 0
 × 1.0λ
 0
 × 0.04λ
 0
. Simulated and measured results show that the single-layer metasurface antenna has a wide 10 dB impedance bandwidth of 23.4 % (24.5 - 31 GHz) (23.4 %) and overlapping 3-dB axial ratio bandwidth of 16.8 % (25 - 29.6 GHz). The antenna also offers stable radiation patterns with a high radiation efficiency (>95%) and a flat gain of 11 dBic. Moreover, a 4-port (2 × 2) MIMO antenna is designed using the proposed design by placing each element perpendicular to each other. Without a dedicated decoupling structure, the MIMO antenna shows an excellent diversity performance in terms of isolation between antenna elements, envelope correlation coefficient, and channel capacity loss. Most importantly, the operational bandwidth of the antenna covers the millimeter-wave (mm-wave) band (25 - 29.5 GHz) assigned for 5G communication. These features of the proposed antenna system make it a suitable candidate for 5G smart devices and sensors.

/pdf/metasurface-based-single-layer-wideband-circularly-polarized-36hrkzr7us.pdf

Metasurface-Based Single-Layer Wideband Circularly Polarized MIMO Antenna for 5G Millimeter-Wave Systems

A novel polarization-insensitive metasurface with angular stability for ultra-broadband (from 7 to 12 GHz) backscatter radar cross section (RCS) reduction is investigated. The proposed metasurface is composed of carefully arranged unit cells with spatially varied dimension, which can diffuse reflection uniformly and avoid the reflection in the specular direction. A proposed metasurface sample is fabricated and tested to validate RCS reduction behavior predicted by full-wave simulation software ANSYS HFSS. A more than 10 dB RCS reduction within the entire X-band is observed, indicating our metasurface may be potentially applied to future stealth technology.

Ultra-Broadband Backscatter Radar Cross Section Reduction Based on Polarization-Insensitive Metasurface

A planar antenna array based on checkerboard polarization conversion electromagnetic band-gap (CPC EBG) structures with wideband circular polarization and low radar cross section (RCS) is presented. The array is formed by $2\times 2$ circularly polarized (CP) element antennas fed with a sequential feeding network. On the one hand, CP radiation is obtained due to the polarization conversion characteristic of the metamaterials. A sequentially rotated feeding network is employed for wide operating bandwidth, polarization purity, and radiation pattern symmetry. The measured results show that the array has a wide usable bandwidth of 18.4%, the common part of an impedance bandwidth of 37.3% (4.80–7.00 GHz), a 3 dB axial ratio (AR) bandwidth of 22.5% (5.00–6.27 GHz), and a 3 dB gain bandwidth of 18.4% (4.94–5.94 GHz). On the other hand, the checkerboard arrangement of the EBG structure generates both an in-band and a partial out-band RCS reduction under normal incidence for both $x$ - and $y$ -polarizations. Besides, the proposed array achieves a significant gain enhancement compared to the traditional slot array. The experimental and simulated results are in good agreement.

/pdf/low-profile-circularly-polarized-array-with-gain-enhancement-58j522ae9l.pdf

Low-Profile Circularly Polarized Array With Gain Enhancement and RCS Reduction Using Polarization Conversion EBG Structures

A novel metasurface (MS)-based method for broadband radar cross section (RCS) reduction of circularly polarized (CP) patch antennas is proposed. The RCS reduction is achieved in a much broader band than the operational band of the antenna. The simple technique is based on MS units on a grounded substrate in a checkerboard-like configuration. The broadband RCS reduction is achieved by combining two different destructive interference principles. In the high-frequency region, for a normal incident wave, the RCS is reduced by the phase cancellation generated by the MSs and the grounded substrate. In the low-frequency region, the RCS is reduced by the polarization conversion property of the MS. In this case, the fields reflected by two MS sections are in counter phase for a normal incident wave. The MS is combined with a CP patch antenna. It concerns a traditional corner-truncated square patch and four sequentially rotated surrounding MS cells. This dedicated MS allows two things: an additional resonant mode is excited resulting in a 3 dB AR bandwidth extension from 4.2% to 15.9% and a broadband RCS reduction of over 6 dB from 4.95 to 15.73 GHz (104.25% bandwidth) for both $x$ - and $y$ -polarized incident waves.

A Broadband Low-RCS Metasurface for CP Patch Antennas

In this study, a dual-broadband reflective polarisation converter with high efficiency for both linear-to-linear and linear-to-circular polarisations based on a metasurface is proposed. Owing to the characteristics of strong anisotropy and multi-order plasmon resonances, the proposed polarisation converter can rotate an y 
/
 x polarised electromagnetic wave to its cross-polarised (
 x 
/
 y 
) direction in the lower frequency band of 7.74–14.44 GHz (a fractional bandwidth of 60.4%) with over 0.9 polarisation conversion ratio. Besides, the proposed structure can also convert a linearly polarised incident wave to a circularly polarised one after reflection in the higher frequency band of 14.95–17.35 GHz (a fractional bandwidth of 14.9%). The performance in the two bands can be controlled separately by altering the proper parameters of the structure. Numerical analysis is used to predict the polarisation states of the proposed polarisation converter. Moreover, the physical mechanism of multiple resonances is discussed based on surface current distributions. A prototype of the polarisation converter is fabricated and measured. A reasonable agreement between the experiments and simulations is obtained. The design has a simple and scalable geometry, and is a good candidate for polarisation control devices in microwave, terahertz and optical frequency regions.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-map.2019.0984

Chenjiang Guo

Papers

Wideband Metasurface-Based Reflective Polarization Converter for Linear-to-Linear and Linear-to-Circular Polarization Conversion

Ultra-Broadband Backscatter Radar Cross Section Reduction Based on Polarization-Insensitive Metasurface

Low-Profile Circularly Polarized Array With Gain Enhancement and RCS Reduction Using Polarization Conversion EBG Structures

A Broadband Low-RCS Metasurface for CP Patch Antennas

Dual-broadband highly efficient reflective multi-polarisation converter based on multi-order plasmon resonant metasurface