The purpose of this paper is to provide simple analytical homogenization methods for composite materials containing a metallic wire grid. Estimating their effective electrical properties facilitates the numerical simulation of composite structures for shielding applications in the automotive industry. The presented methods are based on surface impedance approaches and effective media theory. The obtained results show that the shielding properties of the described wire grid composites can be accurately estimated and bounded, using the proposed theories in the low frequency range. The frequency limits vary according to the studied sample. For the presented materials, the validity of the results is shown to be up to a few megahertz. The experimental validation is done by measuring the shielding effectiveness of composite samples using a near-field test bench.

We hereby present a new equivalent circuit model including both lumped and distributed elements for GCPW-MS transitions (GCPW for Grounded Coplanar Waveguide and MS for Microstrip). In order validating the modelling results, such transitions have been fabricated on a 20 µm-thick BCB (Benzocyclobutene resin) substrate using grounding pads including via-holes of different diameters. The study focuses on the impact of the via-hole design on the performance of the transition and more specifically on its bandwidth. The transitions were made using a simple technological process based on photosensitive polymer. ADS simulation data of the new equivalent circuit model were in very good agreement with measured S-parameters. Both theoretical and experimental results show that the bandwidth of such a transition can reach up to 100 GHz bandwidth using via-holes of 900 µm diameter.

The quaternion multiple signal classification (Q-MUSIC) algorithm reduces the dimension of covariance matrix, which would result in performance degrading of DOA estimation. An augmented quaternion MUSIC algorithm (AQ-MUSIC) based on concentered orthogonal loop and dipole (COLD) array is presented in this paper. The proposed algorithm uses an augmented quaternion formalism to model the completely polarized signals, which allows a concise and novel way to an augmented covariance matrix. The fact reveals that more accurate DOA parameters could be extracted from an augmented covariance matrix. Even compared with the long vector MUSIC (LV-MUSIC) algorithm whose dimension of covariance matrix is the same as AQ-MUSIC, the accuracy of DOA parameter estimation is also improved. Simulation results verify the performance promotion of the proposed approach.

A wideband coplanar waveguide (CPW) fed monopole antenna designed for Wi-Fi5 and Wi-Fi6 applications is proposed. The proposed antenna (main radiator) has a designed footprint of only 20 × 8.7 × 0.4 mm³, which is composed of an oval-shaped ring radiator with three concentric rings and a double-T structure loaded with a J-shaped slot. The main novelty of this work is that the measured wideband operation of 34.5% (5.15-7.29 GHz) is contributed by only a single resonance at 6.2 GHz, conforming to the bandwidth requirement of Wi-Fi5 (5.15-5.85 GHz) and Wi-Fi6 (5.925-7.125 GHz). Furthermore, the proposed antenna also exhibits good radiation characteristics, including a gain around 2.25 dBi, a radiation efficiency above 80%, a total efficiency above 70%, and omnidirectional radiation patterns with a low magnitude of cross polarization throughout the bands of interest.

Different global and national electromagnetic regulatory standards have been developed based upon significantly diversified premises, developmental backgrounds and objectives to safeguard life. Some standards aim at minimizing short duration thermal effects, some try to mitigate non-thermal effects over prolonged duration and rest have adopted precautionary limits. As a consequence, these global and national electromagnetic standards substantially differ from each other. Moreover, in spite of lossy dielectric nature of plant tissues, electromagnetic energy absorption rate level estimations for a complete plant model have neither been reported in literature nor been considered while preparing safety standards. To this end, Specific Absorption Rate levels have been estimated for a typical Catharanthus roseus plant model --- typical geometric shape of the plant prototype has been modelled considering the most practical scenario. Detailed analyses on variation of Specific Absorption Rate levels due to wide discrepancy among the existing electromagnetic regulatory standards have been reported in a quantitative manner. This particular work encompasses dielectric properties measurement of different Catharanthus roseus plant samples, modelling a typical Catharanthus roseus plant containing leaves, flower and twig with appropriate dielectric properties defined, and finally the simulation-based investigations to estimate the variation in Specific Absorption Rate levels based on the contrasting electromagnetic exposure standards. Specific Absorption Rate levels have been reported at five different telecommunication bands as per two occupational and four public exposure scenarios. Variations among the estimated Specific Absorption Rate levels have been noted to be significant and presented in detail in this article. A total of thirty rigorous simulations have been carried out along with one hundred and twenty Specific Absorption Rate data evaluations to ensure accurate comparison among different electromagnetic standards. Noted vast variations among estimated Specific Absorption Rate levels based on contrasting electromagnetic standards over the frequencies indicate the necessity of re-evaluating all existing guidelines and also call for the need of maintaining a global uniformity among the existing electromagnetic standards worldwide.

The propagated fields within and radiated fields outside a rectangular dielectric cylinder are represented as guided and radiation modes respectively. These fields of the cylinder are related with incident, backward scattered fields at x=0 and transmitted fields at x=a by Mode Matching technique. The expressions for guided and radiation mode amplitudes are derived by applying the orthogonal property of the modes. The unknown functions (mode amplitudes) in each of these equations that are defining discrete functions of the guided modes field and angular spectrum for the radiation field are determined numerically. The powers due to discrete guided modes (even and odd) are calculated. The integrals related with the backward and forward scattered fields and the powers associated with them are approximately evaluated by the method of steepest descents.

A method of loaded patch antennas with shorting pins and erected walls in between patch antenna arrays is introduced to reduce surface wave and free space wave coupling in both E and H-plane. This simple technique works equally well in both orientations by reducing coupling up to -19 dB and -15 dB (measured value) in E-plane and H-plane, respectively, as compared to a conventional patch antenna array. The scattering parameters are studied, and conclusions are made on amounts of mutually coupled power and the bandwidth of the rejection band (S₁₂). A parametric study of the variation in the level of mutual coupling with respect to height of the wall has been carried out in both E and H-planes. The simulation results are well verified through measurements.

This work presents a noninvasive measurement technique to detect the blood glucose level for diabetic individuals using a fractal microwave resonator printed on an FR-4 substrate. The proposed fractal is based on the 1st order of Minkowski open loops (MOL) coupled with an open-stub transmission line (OSTL) to increase the resonator selectivity at 2.45 GHz. Moreover, an air gap in the middle path of the OSTL is filed with multi wall carbon nanotubes patch (CNT) to increase the field fringing at a specific region. The proposed resonator is designed numerically with CST Microwave Studio. The size limitations for biomedical devices are considered to account for wearable applications. Later, an analytical study is presented on the proposed resonator sensitivity. The detection technique is based on the resonant frequency tuning, bandwidth variation, impedance matching change, and phase displacement for the S-parameters in the S₁₁ and S₁₂ spectra. The sample under test is mounted on an CNT patch of the OSTL which employs the characterization of the specimen. The proposed design idea could be generalized for a wide variety of biomedical detection liquids.

An accurate rigorous modal theory has been applied to investigate the propagation characteristics in a rectangular waveguide filled with multilayer left-handed and right-handed metamaterials. It is shown that such a waveguide supports different passbands below the waveguide's cutoff frequency, and the number of passbands is related to the corresponding layers of different left-handed metamaterials (LHMs) filled in the waveguide. The rigorous modal analysis of this structure reveals in detail how the waveguide geometry and left-handed metamaterial parameters may be selected to design rectangular waveguides supporting double or triple below-cutoff passbands. The efficient power transmissions in these below-cutoff passbands are validated by using the full-wave simulation software HFSS. These structures supporting multiple below-cutoff passbands could find applications in waveguide components requiring miniaturization and multiband properties, such as miniaturized multifunctional antennas and filters.

Wireless communication plays a vital role in transmitting information from one point to another. Wireless devices have to be smart, intelligent, compact in size and cost effective to meet the demand of wireless communication. A multi-layered, Split Ring Resonator (SRR), negative permeability material inspired antenna has been designed, analyzed, fabricated, and measured. The developed antenna resonates at 1.13 GHz, 2.47 GHz, and 2.74 GHz frequencies with gain of 3.73 dBi, 6.18 dBi, 1.35 dBi, and bandwidth of 2.10%, 2.81%, and 2.09%, respectively. The structure utilizes FR4 material as a substrate. The engineered model has applications in navigation, WiFi, and satellite communication applications.

This paper presents a fifth-generation (5G) wireless smart antenna for performing both power substation communication (in space domain beam-steering) and electrostatic discharge (in time domain Ultra-high Frequency ``UHF'' impulse) detection. The same smart antenna used to communicate with other wireless antennas in the switchyard, as well as with the control room is utilized to cyclically gather data from power apparatus, busbars and switches where electrostatic discharge (ESD) may occur. The ESD poses a major threat to electrical safety and lifetime of the apparatus as well as the stability of the power system. The same smart antenna on which beam rotation in space-domain is designed by implementing an artificial neural network (ANN) is also trained in time-domain to identify any of the received signals matching the ultra-high frequency band electrostatic discharge pulses that may be superimposed on the power frequency electric current. The proposed system of electrostatic discharge detection is tested for electrostatic pulses empirically simulated and represented in a trigonometric form for the training of the Perceptron Neural model. The working of the system is demonstrated for electrostatic discharge pulses with rising times of the order of one nanosecond. The artificial intelligence system driving the 5G smart antenna performs the dual role of beam steering for 5G wireless communication (operating in the space domain) and for picking up any ESD generated UHF pulses from any one of the apparatus or nearby lightning leaders (operating in the time domain).

In wide-angle synthetic aperture radar (SAR), the scattering behavior of many illuminated objects might vary with the observation angle, which results in the degradation of the resolution and interpretability of the reconstructed imagery. To solve this problem, a sparse-based methodology is proposed in this paper to implement the separation of the anisotropic scattering target data and imaging processing simultaneously. The distinct reflection characteristics of the illuminated targets are employed to formulate a composite projection operator. Then, the sparse constraint is utilized to suppress cross-projection energy. Finally, the imagery of the anisotropic scattering targets could be derived with improved focal quality and interpretability. Numerical simulations could verify the validity of the proposed methodology.

In this paper, a substrate integrated waveguide (SIW) quasi-uniform leaky-wave antenna (LWA) is proposed for a dynamically steerable beam design at a single frequency through the use of a thin layer of nematic liquid crystal (LC) underneath the substrate. The orientation of the LC molecules, and therefore the effective dielectric properties of the LC cell, is controlled via an externally low-frequency, low-strength bias voltage. The radiation occurs through a series of closely placed transverse slots etched on the top plane of the SIW. This antenna was designed to operate based on the fundamental space harmonic (n=0) in the frequency range between 24.25 GHz and 29 GHz, which covers one of the future 5G frequency bands to be deployed in some parts of the world. This novel antenna design concept was verified numerically using a commercial software based on the Finite Element Method (FEM), and the results are presented and discussed herein.

For the first time, a real sized complex target that is coated with an absorber material is discriminated from the uncoated one using an aspect independent discrimination method based on natural resonances. This resonance based technique provides a real-time, accurate and aspect independent solution for stealth target discrimination. First, the discrimination is studied for a complex shaped aircraft of electrical size 1.5λ. The Perfectly Electrically Conducting (PEC) target is coated uniformly with sintered nickel-zinc-ferrite, a magnetic Radar Absorbing Material (RAM) with complex dielectric and magnetic properties. The resonant range Radar Cross Section (RCS) of the aircraft for different coating thicknesses is computed using the Method of Moments (MoM). The resonances contained in the RCS are extracted using the vector fitting method, and the dominant resonances representing the target are determined by applying the power criteria. The variation in the pole placements with the increasing coating thickness is also studied. A one number quantifier of discrimination --- ``Risk'' in dB is defined to express the amount of mismatch between the compared targets. Further, the discrimination technique is also studied for an aircraft of electrical length, 7λ. A Risk value of 2 dB and more is obtained in this study at all aspects. This demonstrates the capability of the algorithm to discriminate between targets of identical structure but with different material compositions.

Designs of a polygon shape microstrip antenna for increasing number of side lengths are studied. A detailed analysis is presented for the variations observed in the first and second order mode resonance frequencies in a polygon shape patch, from triangle to square to pentagon, ending up in a circle. Among all the polygon shapes, close spacing between the first two frequencies is obtained in the pentagon shape patch. A design of a pentagon shape microstrip antenna with a pair of slots is proposed. It gives impedance bandwidth of more than 700 MHz (>55%), which is maximum amongst all the polygon shapes employing a pair of rectangular slots. The proposed design offers peak broadside gain of 9 dBi over the bandwidth. A resonant length formulation and subsequent design methodology for the pentagon shape patch and its slot loaded variation are presented. This helps in the redesigning of a similar configuration in a given frequency range, using proximity and coaxial feeds.

A compact wearable antenna operating at 2.45 GHz with a novel Electromagnetic Band Gap (EBG) structure as a reflector is proposed. The broadband monopole is used as the main radiator of the antenna, and the gradient feeder structure and etched slot on the ground are used to adjust the matching effect of the antenna port. The current path is extended, and the structure is made more compact by slotting the surface of the EBG cell. Then, a 3 x 3 EBG reflector is constructed and loaded to the bottom of the antenna to improve the antenna gain performance and reduces the specific absorptivity (SAR). A three-layer human model (skin-fat-muscle) has been built in High Frequency Structure Simulator (HFSS) to analyse the influence of human tissue on the wearable antenna system. Combined with the practical application background, the radiation performance of the system under bending is also explored. The simulation results show that the application of EBG reflector can increase the antenna gain by about 4.77 dBi and the front-to-back ratio by 17dB, reduce SAR by more than 95%, and the overall size of the system is only 60.3 x 60.3 x 3.5 mm³ (0.49λ). The antenna system has the characteristics of simple structure, small size, high gain, and low SAR value, which is of certain reference value for the research on the wearable antenna.

In this article, a meander line dipole antenna for radio frequency identification (RFID) tag is presented. The loaded meander antenna has a simple meander line structure with a spiral inductor at the end for size miniaturization, a T-match structure and an inductively coupled parasitic element for impedance matching with the tag IC. The antenna is designed to operate in North American UHF RFID frequency band of 915 MHz. The size of the proposed tag antenna is 50 mm × 12 mm and has good impedance matching with Alien Higgs IC chip of 13.5-j111 Ω at the desired frequency band. The proposed tag antenna provides omnidirectional radiation pattern with a maximum read range of 3.5 m at an effective isotropic radiated power of 4 W. Simulation results are in good agreement with measurement results.

A novel computational technique is proposed for heat conduction analysis. The heat transfer equation is expanded in the complex frequency domain and solved using the finitedifference method (FDM). The results in the complex frequency domain are transformed into the time domain via fast inverse Laplace transform. In the proposed approach, the instantaneous temperature at a specific time can be easily obtained. Moreover, the computational time for the conventional explicit FDM is reduced by employing the time-division parallel computing method.

We recently proposed a two-dimensional synthetic space including one spatial axis and one synthetic frequency dimension in a one-dimensional ring resonator array [Opt. Lett. 41, 741 (2016)]. Nevertheless, the group velocity dispersion (GVD) of the waveguides that compose rings was ignored for simplicity. In this paper, we extend the previous work and study the topological one-way edge states in such a synthetic space involving GVD. We show that the GVD brings a natural vague boundary in the frequency dimension, so the topological edge state still propagates at several frequency modes unidirectionally along the spatial axis. Positions of such vague boundary can be controlled by changing the magnitude of the GVD. In particular, a relatively strong GVD can degrade this two-dimensional synthetic space to one-dimensional spatial lattice, but yet the one-way state is still preserved in simulations. Our work therefore exhibits the impact of the GVD on topological photonics in the synthetic space, which will be important for future practical experimental implementations.

A compact U-shaped ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna with novel complementary modified Minkowski fractal (CMMF) for isolation enhancement is proposed. This antenna consists of two identical U-shaped monopole elements, a novel CMMF and a slot in the bottom of the ground plane for the isolation enhancement. The novel CMMF is designed by a technique iterated function system (IFS). The overall dimension of this compact antenna is 22 x 28 mm². The impedance bandwidth of this antenna is 10.35 GHz, ranging from 3.06 GHz to 13.41 GHz. The minimum isolation is 17.07 dB for the operating frequency range and 18.4 dB for the UWB frequency range 3.1 to 10.6 GHz. The diversity parameters are also determined for the proposed MIMO antenna, and all are found satisfactory. The proposed MIMO antenna is fabricated, and its prototype measured results are found in good agreement with the simulated ones.