Vol. 132

In this paper, the authors address the issue of the flux-modulated magnetic gear (FMMG), which offers many potential advantages over traditional mechanical gears for a wide range of applications. In the proposed FMMG model, two permanent magnet (PM) carriers are of different pole-pairs and rotate asynchronously, and their relative angular position with respect to the pole parts of the flux modulator is not as straightforward and simple as it may seem in conventional electrical machines. Therefore, this paper focuses on the details of the derivation of the FMMG load angle, which attempts to better express the angular relationship between the individual components of an FMMG. Finite element method (FEM) simulations and experiments are used to validate the load angle concept and corresponding results, and are complemented by experimental measurements. It is believed that the concept of loading angle can facilitate the design and simulation of FMMG and magnetically geared machines (MGM) based on the finite element method under different loading conditions.

To solve the problems of traditional reflective metasurfaces that cannot change the focal position and have simple functions, a polarization multiplexed 1-bit reconfigurable metasurface is proposed. It can realize the independent focusing characteristics of the x-direction polarization and y-direction polarization incident waves. The metasurface unit consists of a layer of dielectric substrate with a thickness of 0.055λ, a metal element embedded with a pair of PIN diodes, and ground. Two diagonal slits on the ground can not only be used as a reflection ground to keep high reflection, but also behave as a bias control line to control the voltage to change the state of the PIN diodes. Optimizing the structure parameters of the metasurface unit, the reflection phase can be manipulated binarily between 0 and 180°, corresponding to ON and OFF states, respectively. Based on the principle of quasi-optical path, a polarization multiplexed 1-bit reconfigurable metasurface with independent dynamic focusing characteristics at 11GHz is designed. On this basis, by changing the polarization direction of the incident wave, the dual-focus distribution with different power ratio can be obtained. The proposed 1-bit reconfigurable metasurface has no multilayer metal elements and complex feeding structures, and has the characteristics of a simple structure, low profile, and multifunction. At the same time, it enhances the utilization of metasurface array and provides a higher degree of freedom for wireless power transmission applications in future.

A conical horn antenna fed by a cavity-backed two-layered suspended microstrip antenna has been proposed. The overall compact antenna with a length of 2.3λ₀ yields a wide impedance bandwidth of 57% centred around 2.8 GHz with a very high gain of 19.9 dBi, an average gain of 17.5 dBi and a radiation efficiency of above 88%. In effect, the gain of the basic two-layered suspended microstrip antenna is enhanced by 8.4 dB when it is backed by the cavity and the conical horn. A good radiation characteristic is obtained throughout the impedance bandwidth with main beam stability, high isolation between two such antennas and low cross-polarization. Over the entire operating bandwidth cross-polarization lower than -30 dB with co-cross polarization isolation better than 50 dB is obtained in 45˚ plane. In comparison to conventional conical horn antennas yielding the same gain, the proposed antenna is more efficient with only 45% length. The prime contribution of the work is the concurrent yield of high 19.9 dBi gain, wide bandwidth, high efficiency and good radiation characteristics including unidirectional stable radiation patterns, low cross pol. and high isolation between antennas which has not been reported so far. The proposed antenna is designed for various S-band FMCW Radars.

This paper proposes a microstrip-fed simple square slot patch antenna, which produces a triple band and is circularly polarized. The designed antenna consists of an L-shaped patch radiator in which the lower part of L is modified to a circle instead of a rectangle, and two rectangular strips are inserted from the opposite corners of the ground plane. Two small rectangular slits have also been used in the design to generate the triple band and widen the bandwidth too. The antenna has been fabricated and measured and it shows a good agreement between them. The measured impedance bandwidths (IBWs) are 44.06% (2.3-3.6 GHz) and 73.68% (4.8-10.4 GHz), and the axial ratio bandwidths (ARBWs) are 37.29% (2.4-3.5 GHz), 13.6% (4.8-5.5 GHz), and 32.35% (5.7-7.9 GHz) in the lower, middle and upper band respectively.

A compact wideband miniaturized electromagnetic band gap (EBG) antenna has been proposed for communication systems with E-shaped defected ground structure (DGS). The proposed EBG antenna operates in the frequency range from 7.3 GHz to 9.4 GHz which includes the X band uplink frequency band (for sending modulated signals) from 7.9 to 8.4 GHz and the ITU-assigned downlink frequency band (for receiving signals) from 7.25 to 7.75 GHz. With EBG layer on the top layer, an E-shaped DGS structure has been introduced in the ground plane which results in the enhancement of measured impedance bandwidth from 300 MHz to 2100 MHz with good radiation characteristics.

In this study, a tri-band wearable antenna with a metal frame of 36×36×6.6 mm³ is designed, fabricated, and measured based on the characteristic mode theory. By analyzing the current and electric field distribution of the characteristic mode, the antenna is determined to be fed by a T-coupled structure. Moreover, a circular ring ground structure is added to the initial elliptical model structure to generate a new resonance in the n78 band. On the other hand, the current's path is changed by etching a rectangular slot, allowing the high-frequency resonance mode to be shifted to the right. Simulated and measured results show that the proposed antenna covers Bluetooth/Wi-Fi (2.4G, 5.8G) and N78 frequency bands, which can be respectively used for connecting a watch to a mobile phone, accessing the Internet and making phone calls. Furthermore, the antenna has a maximum peak gain of 4.11 dBi in free space and 6.9 dBi when being placed on the wrist, with a Specific Absorption Rate (SAR) lower than international standards, making it suitable for wearable devices.

Limiter is a protective structure that is considered a vital device in microwave systems, especially radars. A limiter operates as a receiver protection against large input power for receiver microwave circuit component protection and allows the receiver to function normally when these large signals are not present. In this paper, the investigation and implementation of a miniaturized microwave substrate integrated waveguide power limiter (SIWL), approximately 43×20.5×135 millimeters cubed, for low power receiver protection in military S-Band portable radar applications are compared with a rectangular waveguide limiter (RWGL), approximately 72.14×64.04×178.05 millimeters cubed, and analyzed using commercial software. The proposed limiter design configurations for receiver protection have been designed, analyzed, and compared with samples of the other literature techniques. The proposed designs have been fabricated, and the microwave characteristics have been illustrated. The measured results of the proposed limiters have been analyzed, and the agreement between the measured and simulated results shows that the proposed limiters provide excellent protection and meet the needs of low power receiver portable radar and communication applications with a design that reduces SIWL size.

In the present study, a broad negative refractive index (NRI) performance is achieved in the terahertz frequency range (0.6-0.9 THz) through the design of multi-layered fishnet metamaterial (FMM). Herein, the conventional fishnet structure is modified by smoothing the sharp corners to reduce the electric field concentration and improve NRI. At corner radius, r = 30 µm, an effective refractive index of -11.14 is achieved with lower electric field concentration at the corners. A multilayer structure of up to 40 layers is studied to achieve a broad NRI frequency response. The frequency band of NRI response is improved from 0.034 THz for a single layer structure to 0.178 THz for 28 layers structure, almost 6 times the original bandwidth. With the increase in the number of layers, improvement in NRI and Figure of Merit (FOM) is observed, and maximum NRI and FOM values of -87.5 and 12.67 are achieved at 28 layers. This multilayer broadband design can surpass tunable response of available electro-optic materials. With an optimal combination of NRI and FOM, the presented multilayer approach can achieve a low-loss, broadband performance.

In antenna design, the low side lobe level (SLL) of the antenna radiation pattern plays a crucial role in communication systems as it reduces signal interference along the entire side lobes of the radiation pattern. This paper presents an effective technique to minimize the SLL and thus improve the radiation pattern of the concentric circular antenna array (CCAA) using an advanced marine predator algorithm (AMPA). The AMPA is inspired by the predator-prey relationship in aquatic ecosystems, and it incorporates an improved adaptive velocity update strategy and a chaotic sequence parameter. In this work, the AMPA is applied to synthesize two examples of CCAA (4, 6, 8-CCAA elements and 8, 10, 12-CCAA elements) under two different instances (without and with a centre element). The simulation results achieved a significant improvement in SLL minimization as compared to the uniform array, the standard marine predator algorithm (MPA), and some other nature-inspired metaheuristic algorithms.

This article investigates a Turbinella-shaped super wideband monopole antenna designed to accommodate the attributes of the fifth-generation (5G) technology which is the enhanced Mobile Broadband (eMBB). The antenna is designed to work with the current millimetre wave bands, including n77, n78, and n258, and it provides the increased data rate needed for eMBB applications. The proposed antenna comprises a Turbinella-shaped patch, a 50 Ω tapered feed line, and a multi-slotted partial ground plane. The self-similarity and space-filling nature of circular geometrical fractal is employed in a novel way to acquire the antenna compactness and broadband performances. Further with the design of a tuning fork-shaped Defective Ground Structure (DGS), super wideband characteristics to incorporate 5G millimeter bands are obtained. The proposed antenna has a compact size of 0.25λ × 0.32λ along with a bandwidth of 173.33% along the frequency ranging from 3 to 41.97 GHz and has achieved a compactness of 81%. Moreover, the fundamental dimension limit theorem is used to demonstrate the antenna's compactness. Time domain analysis is also studied in this article.

In this paper, a new type of defected ground structure (DGS) antenna based on metamaterial is presented. The proposed antenna has the performance of global bandwidth and gain improvements. The miniaturization of the antenna can be achieved by loading metamaterials on the DGS antenna to reduce the resonance frequency of the antenna. Due to the coupling effect between the metamaterial and the DGS, multiple resonant points are generated, thus extending the impedance bandwidth of the antenna. The impedance bandwidth of the proposed antenna ranges from 3.5 GHz to 6.32 GHz (56.6%). The degree of miniaturization is 37.9%, and the measured peak gain is 4.5 dB. The size of the antenna is only 0.35λ₀ × 0.35λ₀ × 0.011λ₀, which has a highly stable antenna efficiency of greater than 90% over the entire operating bandwidth. The proposed antenna is suitable for WLAN and Bluetooth applications.

In this paper, a planar tag antenna for UHF band RFID composed of a spiral ending meandered line with meandered inductive loop is presented. The presented novel compact spiral ended meandered tag having double sided meandered inductive loop microstrip dipoles scales down the extent of tag antenna and provides an upgraded conjugate impedance matching between tag antenna and semiconductor ASIC. This tag antenna operates at 866 MHz. Here, a compact UHF tag having volume of 60 × 16 × 1.6 mm³ (0.173λ × 0.046λ × 0.0046λ) is testified. This antenna produces impressive reflection coefficient and is able to access detection territory of 12.6 m. The proposed RFID antenna layout is simulated in favor of reader having 4 W EIRP.

Globally, microwave frequencies are being extensively employed in numerous biomedical implementations due to its high resolution, reasonable penetration through the human tissue, and cost-effectiveness. However, the quantization of human osseous tissue through microwave sensing is still not proficient. Therefore, this article provides an insight on the prediction of onset and progression of osteoporosis developed through the use of a microwave setup for the contactless evaluation of osteoporosis. This microwave setup comprises a human wrist model as a device under test which is illuminated through a pair of planar stubbed monopole antennas to characterize the different degrees of osteoporosis through frequency domain simulation analysis. By diversifying the wrist dimensions, we are collecting the dataset of the transfer characteristics. Furthermore, different machine learning algorithms are employed on this dataset to train, classify and eventually evaluate the different degrees of osteoporosis. Finally, an optimum machine learning algorithm was obtained to work at an optimum bandwidth and optimum frequency.

The paper presents a new technique for designing a reconfigurable frequency selective surface (RFSS) by mechanical means. The combination of triangular loop element and three-legged element has been used to design the proposed single substrate two sided frequency selective surface (FSS) structure which offers variable transmission coefficient characteristics over the X-band frequencies under TE polarization for different angles of incidence. Thus, the band stop characteristics can be reconfigured by changing incident angle which describes the structure as `reconfigurable reflector'. The proposed FSS geometry is polarization insensitive under both TE and TM polarizations. The simulated results are further cross verified by conducting measurement of the fabricated structure. The equivalent circuit model (ECM) of the proposed FSS geometry has been provided, and the equivalent circuit parameters of the proposed FSS geometry have also been extracted using the curve fitting techniques. The proposed FSS structure can be used as a frequency reconfigurable reflector surface/reconfigurable intelligent surface (RIS) for advanced wireless communication.

A simple and flexible differential negative group delay (NGD) circuit topology based on defected ground structure (DGS) is proposed. The circuit consists of microstrip lines and reverse nested double U-shaped (RNDU) DGSs, in which differential transmission and common-mode suppression (CMS) are realized by microstrip lines, and the adjustment of NGD time and the center frequency is achieved by changing the RNDU DGSs. Besides, the bandwidth and NGD time can be increased by cascading double couples of RNDU DGSs. For demonstration, two circuit prototypes with single- and double-couple DGSs are fabricated and measured. The measured results show that the NGD time of the single-couple DGS circuit at the center frequency of 2.279 GHz is -0.57 ns; the insertion loss is 2.08 dB; and the NGD bandwidth is 28 MHz. The NGD time of the double-couple DGS circuit at 2.30 GHz is -2.13 ns; the NGD bandwidth is 41 MHz; and the insertion loss is 4.39 dB. The functions of increasing bandwidth and enhancing NGD are realized. The common-mode insertion loss can reach 43.2 dB, and excellent CMS characteristics are achieved.

A multi-resonating coplanar waveguide (CPW) fed flexible antenna using metamaterial unit cell is designed for various UWB wireless communication systems. The designed unit cell has the total dimension of 14.8 mm × 14.8 mm × 0.25 mm. The top layer of the cell has a circular ring slot combined with four modified T shaped radiators giving metamaterial characteristics. The unit cell uses perfect boundary conditions along with y axis wave propagation, and it gives wide NRI region covering 2 to 16 GHz of frequency range. The overall gain of proposed CPW fed antenna is increased by using a 3 ×3 metamaterial array as reflector at the back of antenna. The metamaterial antenna has 2 to 16 GHz of total bandwidth and peak gain of 13.1 dB. Further the measured outcomes are in accordance with the simulated ones.

A study is made of the guiding properties of a nerve fiber consisting of myelinated axons as applied to electromagnetic waves in the optical and infrared ranges. Based on rigorous expressions for the electromagnetic field in the presence of a nerve fiber, the dispersion properties and field structures of eigenmodes guided by the fiber are analyzed for different values of the dielectric permittivity of myelin. It is shown that such a complex waveguide of natural origin can support the propagation of weakly attenuated eigenmodes in the considered ranges. It is shown that the dispersion properties and field structures of the modes of the nerve fiber can differ significantly from those of a single axon.

This work describes the design and analysis of a four-element wideband circularly polarized (CP) Multiple-Input-Multiple-Output (MIMO) antenna for mid-band 5G utilizations. The proposed MIMO antenna miniaturization is obtained by the implementation of composite right/left-handed (CRLH) transmission line (TL) and loading of octagonal shaped slotted rings inside the antenna ground plane. Further, the circular polarization radiation is obtained due to the sequence arrangement of two CRLH-TL based unit cells of opposite branches, inside a conventional square patch. The intended MIMO antenna encompasses two layers, the layer-1 consists of a four-element CRLH-TL based circularly polarized MIMO antenna placed in side-by-side configuration. The layer-2 consists of 3×3 square-shaped metasurface on one side and an octagonal slotted ring on another side. The combination of two layer results in wider bandwidths of 68.84% (2.21-4.53) and 3 dB axial ratio (AR) bandwidth of 30.4% (3.1-4.21 GHz). Furthermore, the antenna has better than 10 dB isolation, a maximum gain of 7.2 dBi at 4.04 GHz, radiation efficiency of more than 65%, and lower envelope correlation coefficient (ECC) values across the whole operating band. Diversity Gain (DG) values are high and near to 10 dB. Total Active Reflection Coefficient (TARC) and Channel Capacity Loss (CCL) values are also very much acceptable. As a result, the suggested four-element MIMO antenna is appropriate for midband 5G utilizations.

This paper presents a new simplified procedure to design a fourth-order coupled resonator filter. This procedure does not require the calculation of complicated Eigenvalues to develop the required coupling matrix. It starts with studying the effects of different coupling mechanisms on the performance of the overall filter structure. Then, these coupling mechanisms are combined to obtain the design of the required filter. This procedure may be more suitable for machine learning procedure to design coupled-resonator filters. The proposed method is used to design a substrate integrated waveguide (SIW) bandpass filter for sub-six GHz 5G applications. The designed SIW bandpass filter operates in the frequency range from 3.7 GHz to 3.98 GHz which covers the New C-band 5G network with a fractional bandwidth (FBW) of 28% and is centered at 3.84 GHz. This filter is fabricated and measured for verification.

A multiband electromagnetic band gap (EBG) structure is designed and implemented with a multiband MIMO antenna for mutual coupling reduction. An area of 16 × 16 mm² on a low cost FR4 substrate is used for the proposed EBG design. The designed E-coupled slotted U-shape MIMO antenna resonates at 5.7 GHz, 7.5 GHz and 10 GHz frequencies. Edge to edge separation between the two antennas is kept as 6 mm. EBG structure is placed in the ground plane between two antennas that enable us to keep separation of antennas less than the size of the EBG. Mutual coupling gets reduced by 6.6 dB for 5.7 GHz, 4 dB for 7.5 GHz and 6.95 dB for 10 GHz. Simulated radiation properties of MIMO antenna are verified by measured results, and surface current distribution of MIMO antenna surface also verifies the mutual coupling reduction. Envelope correlation coefficient < 0.01 and channel capacity loss < 0.2 are achieved at resonating frequencies.