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.

Terahertz era is becoming a more prominent and expanding platform for a variety of applications. In this paper, we propose a triband absorber with a hexagon-shaped radiating patch for THz applications. The proposed structure has three layers: a hexagonal patch made of graphene as a radiating patch, a silicon layer as a dielectric substrate, and a bottom conductive layer made of gold to prevent EM wave transmission. The proposed structure operates at three resonant frequencies 0.38 THz, 1.23 THz, and 1.77 THz respectively. We may accomplish maximum absorption level (above 90%) and maximum absorption bandwidth by setting relevant chemical potential and relaxation times to 0.2 ev and 0.2 ps respectively. The proposed structure contains a lossy silicon substrate, which has a dielectric constant of 11.9 and a loss tangent of 2.5e-004. The proposed structure reveals a larger absorption [above 90%] for the operating frequencies, and the effect on absorbance for different modes is illustrated.

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.

This letter addresses a new approach to improve the gain and isolation of a multiple input multiple output (MIMO) antenna. A C-shaped printed antenna with both ends terminated by a small rectangular section is designed as the basic antenna element for a 2 element MIMO antenna of size 0.8λ×0.67λ×0.04λ (λ, corresponding to lowest operating frequency) which operates over the X band with peak gain of 3 dBi. By introducing a double layered frequency selective surface (FSS) of unit cell dimension 0.2λ×0.2λ×0.0375λ between the two antenna elements as an isolation wall and additionally by placing a 5×3 array of FSS geometry as a reflector below the antenna, the isolation and gain of the two element MIMO antenna are improved by 37 dB and 3 dBi, respectively. The proposed FSS loaded MIMO antenna provides very high isolation about -51 dB (measured) and a very low envelope correlation coefficient (ECC) of 0.000177282 (simulated) using far field approach and 0.000000033414 (calculated measured) using scattering (S) parameter approach. Further MIMO parameters like diversity gain (DG), total active reflection coefficient (TARC), mean effective gain (MEG) and channel capacity loss (CCL) have been evaluated. The radiation pattern is unidirectional in nature with a peak gain about 6 dBi. The letter also presents detailed design guidelines for the proposed FSS loaded MIMO antenna along with their verifications for Ku and K bands. The proposed structure can also be scaled up to a 4 element MIMO antenna.

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.

Solid State Transformers (SSTs) are emerging as the major component of smart grid system. High Frequency Transformer (HFT) is the key element of SST. The optimum design of SST is a critical task due to the complex design of magnetic, electric and dielectric circuits of high frequency transformer and due to the design of power electronic circuits used at either sides of HFT. The most significant among above is the design of magnetic circuit and the possibility of using different magnetic materials for high frequency application. This paper discusses the performance analysis of HFT for different magnetic materials used for core construction. The magnetic materials considered in this analysis are amorphous, nanocrystalline and si-steel. Optimum HFT design is selected from a set of designs using an iterative algorithm, considering each core material separately. Validation of the design is done in Finite Element Method (FEM) analysis software. The design of a high frequency transformer, which is integrated in 1000 kVA 11 kV/415 V SST, is investigated both analytically and numerically, with optimum designs developed using three core materials.

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.

In this work we show a novel method based on a local two-port interferometer to distinguish the topological charge of radio-vortices at 30 GHz by using a small portion of the entire wavefront only. The experimental investigation of the amplitude and phase properties of the interference pattern with a pure Gaussian beam (l = 0) and a l = 1 radio vortex is carried out, and results are compared with the theory based on Laguerre-Gauss modes. Experiments were performed both with the interferometer and with single antenna to highlight the effective benefits of the interferometric approach, sensitive to the azimuthal phase of the vortex field. Method is also extendable at higher topological charges for applications to high-density millimetric communications.

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 3D printing and printed circuit board (PCB) hybrid fabricated modularized dual-stopband artificial magnetic conductor (AMC)-loaded filtering antenna is proposed for an X-band high-power radar system.By loading low-cost microstrip AMCs of different frequency responses into a waveguide slot array, we achieve a modularized filtering antenna whose frequency response can be simply controlled by replacing different AMCs. The waveguide slot array only works as a fixture to host different AMCs to achieve various filtering antenna frequency responses. The interchangeable modularized design helps to reduce the difficulty and cost of component fabrication by eliminating the need for complex resonant cavities inside the waveguide filtering antenna, which is time-efficient at the stage of product prototyping when numerous iterations are needed on a trial-and-error base. A dual-stopband filtering antenna is designed and fabricated in the X-band to verify the design concept. The passband covers 9.25-10.6 GHz with the passband gain greater than 10 dBi. The antenna radiates frequency-dependent scanning beams in the passband. The stopbands are 8.1-9 GHz and 10.75-11.5 GHz, and the out-of-band rejection is larger than 35 dB. The proposed design concept provides a different thought to achieve a low-cost filtering antenna by using interchangeable modularized components. The fabricated antenna prototype is a capable candidate for high-power airborne radar applications.

A dual frequency dual circularly polarized cross-slot waveguide array working at 4.9 GHz and 5.8 GHz is proposed for wireless communication/airborne weather radar applications. Different from the traditional cross-slotted waveguide antenna, to improve space utilization, two sets of cross-slots are slit on both sides of the longitudinal axis of the waveguide's E-plane to realize dual-frequency operation. When the antenna operates in the TE₁₀ mode, the cross-slots on each side radiate left-handed and right-handed circularly polarized electromagnetic waves at two different frequencies, respectively. To suppress grating lobes, phase perturbation structures are periodically loaded in the waveguide to tune the propagation phase constant, thereby changing the effective electric spacing between radiating elements while keeping the antenna a compact physical aperture. The proposed grating lobe suppression method avoids the dielectric loss caused by dielectric loading, eliminates the need for complex array arrangement, and achieves the grating lobe suppression at dual frequencies simultaneously. The metallic 3D printing technology, selective laser melting (SLM), is used to fabricate the antenna in one piece in one run using aluminum alloy. The proposed antenna has gains of 10 dBic and 14.5 dBic with 47% and 69% aperture efficiencies at 4.9 GHz and 5.8 GHz, respectively. It is a capable candidate for air-to-ground (ATG) communication applications.

This paper presents a new scheme to implement the iterative physical optics (IPO) approximation with edge diffraction for the scattering from large perfectly-conducting objects, for which, multiple reflections occur. The use of the electric field integral equation (EFIE) discretized by the Galerkin method of moments (MoM) with Rao-Wilton-Glisson basis functions leads to solving a linear system. The characteristic basis function method (CBFM) needs to invert the self-impedance sub-matrices to calculate the primary basis functions (PBFs). To accelerate this stage, these sub-linear systems are directly solved from the physical optics (PO) approximation. In addition, to improve the precision of PO, the EFIE-PO self-impedance matrix is derived analytically. This avoids to apply the magnetic field integral equation (MFIE), for which its principal value is related to PO. Numerical results showed that the resulting algorithm, CBFM-PO, predicts inherently the edge diffraction. A domain decomposition method is able to split up the geometry into blocks, for which either the PO or a LU decomposition is applied according to the sub-geometry. To accelerate the coupling steps, the adaptive cross approximation (ACA) is also implemented, and the resulting method is tested on different targets having a curvature and producing multiple reflections. The numerical results show that EFIE-CBFM-PO is more accurate than the conventional EFIE-CBFM-POJ (based on Jakobus et al. work), specially for objects with curvature.

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 quasi-equal inductor filter and its corresponding multilayer realization are proposed in this paper. The circuit transformation is performed using the Norton transformation. In the proposed filter, ratio between the largest and smallest component values is reduced, which makes the design of components much easier. Meanwhile, by carefully selecting the transformation ratio, all grounding inductors are equal in value. As a result, the multilayer filter design is simplified because only one instance of grounding inductors needs to be designed instead of three. An experimental prototype is fabricated and measured. The measurement result agrees well with the desired one, which shows the effectiveness of proposed filter.

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.