This paper proposes a novel electromagnetic band gap (EBG) structure based on a dual-layer dual-patch unit (DLDP-EBG) cell to improve isolation and decrease envelope correlation between MIMO slot antenna array elements. A wideband MIMO slot antenna array operating in the frequency range of 4.2-6.5 GHz (43%) is deployed. The antenna array is based on slotted rectangular microstrip radiating elements printed on the top surface of two stacked FR4 substrates to widen the array impedance bandwidth. A 2 x 7 dual-layer DLDP-EBG unit cell is inserted between the array elements to reduce the mutual coupling and detect the individual beams of each antenna in opposite directions. An isolation improvement of up to 56 dB is maintained throughout the working bandwidth of the antenna, when the EBG is inserted. Also, the DLDP-EBG unit cells reduce the envelope correlation coefficient by 5-30 dB across the whole operating bandwidth by detecting the radiation beams of the individual antenna elements in opposite directions. The MIMO array gain and radiation eciency have been improved after using the EBG structure due to the reduction in mutual coupling and surface wave mitigation between the array elements. The proposed low-prole MIMO slot antenna array is the first in literature to exhibit such wideband isolation improvement, gain enhancement, and correlation reduction behavior simultaneously.

Tunable negative electromagnetic properties: permittivity, permeability, and refractive index, in mimic Chlorophyll metamaterial structures in the X- and Ku-band regimes are theoretically and numerically demonstrated. A very broad negative permeability covering the majority of the X- and Ku bands, from 8 GHz to 16 GHz, is observed, while five negative permittivity bands are found within the same range. The two aforementioned properties result in a broad, greater than 25% bandwidth, low-loss negative-refractive index transmission band. These negative electromagnetic properties can be effectively tailored within the low-loss multi-transmission and the high-loss multi-absorption bands in the operating frequency range by modifying the structure's tiller part or the artificial hydrophobic or Phytol tail. By focusing either on the transmission or the absorption bands, these passive always-on bio-inspired metamaterials could be utilized in microelectronic, communication and photonic, and optic devices.

In this article, the diffraction of plane electromagnetic waves by double half-planes with fractional boundary conditions is considered. As particular cases, the diffractions by wedges and corners are considered for different values of fractional orders. The results are compared to the analytical ones. The interesting properties of wedge diffraction are outlined for intermediate fractional orders.

To predict the residual electric field inside an electromagnetic (EM) shield under illumination of different HEMP waveforms, a method based on NARX neural network is proposed in this paper. The model can be established from input-output data of EM shield without knowing enclosure and internal structural details. To evaluate the precision of the prediction method, two error criteria based on energy and field amplitude are provided in this paper. As a numerical example, the double exponential pulse with 10% to 90% rise time of 2.5 ns, the pulse width at half maximum of 23 ns, and the corresponding residual electric field are taken as the training data. The EM simulation is used to establish the model of residual electric field inside the shield. The NARX neural network is then built and trained. Other double exponential pulses, with different rise times and pulse widths, and their residual field are taken as the checking data. The results show that the error of the prediction method is sufficiently small for actual use.

In this article, the authors present a hepta band metamaterial inspired hybrid fractal octagonal shape antenna for wireless applications. Multiband characteristics in the proposed design are achieved by hybrid fractal form of Moore curve and Koch curve with metamaterial loading. A well matched impedance bandwidth (S₁₁ ≤ -10 dB) is accomplished at seven microwave frequency bands Upper L band (1.93~2.08 GHz), S band WiMAX (3.3~3.7 GHz), C band WLAN (5.4~5.9 GHz), C band IEEE INSAT application (6.5~7.2 GHz), X band terrestrial broadband, space communication and Radio Navigation (RN) application (8.51~11.05 GHz), Lower Ku band direct broadcast satellite service (12.2~12.7 GHz), and Middle Ku band satellite communication operating band (14.73~15.84 GHz) covering various wireless applications. The antenna achieves hexa/penta band characteristics during switching ON/OFF state of PIN diode placed between the Moore curve structure (attached with centered SRR cell) and feedline. Radiation patterns are found in stable forms at all the resonant frequencies. Measured results of the proposed design are compared with simulated ones indicating good agreement between them.

Results of the study of magnetic properties of nanocomposite samples (CoFeZr)_x(CaF₂)_{(100 - x)} (31 at.% ≤ x ≤ 47 at.%) produced in argon (Ar) and argon with oxygen (Ar with O₂) sputtering atmosphere are presented in this paper. The magnetic resonance spectroscopy at room temperature using continuous wave X-band electron spin resonance (ESR) was used for analysis of samples magnetic properties. After analysis it is established that in the case of samples produced in argon sputtering atmosphere the value of g increases with the rise of metal content and for samples produced in argon with oxygen atmosphere the value g decrease with the rise of x. Such a behavior of g(x) is explained by the presence of core-shell structure of NPs represented by ferromagnetic core and antiferromagnetic core that results in quenching of orbital motion of electrons.

A gradient index metamaterial (GIM) based conformal cloak is utilized to reduce the overall scattering of a dipole antenna and its blockage effect when being placed in close proximity of a horn antenna. The reduction in scattering is attributed to wave conversion properties of GIM cover, by virtue of which the propagating waves get converted to surface waves and vice versa, thus reducing the scattering signature of the dipole. The GIM cover also has the advantage of larger bandwidth than single metasurface based cloaks (mantle cloak). The proposed GIM based cloak proves to be effective in reducing the mutual interference between dipole and horn antenna without disrupting the performance of individual antennas in their respective frequency band of interest. The Ansys HFSS simulation results are presented to demonstrate the effectiveness of GIM based cover to reduce mutual blockage effect between a low band dipole and an S-band horn antenna.

In this paper, a dual-band 4-, 6- and 8-element multiple-input multiple-output (MIMO) antenna arrays operating at the sub-6-GHz (LTE 42/43 and 46) bands for the fifth-generation (5G) smartphones are proposed. To realize these three MIMO applications in two LTE bands, miniaturized spiral and meander line-shaped strips coupled-fed patch antenna elements are printed on the front side of an FR4 system circuit board and are able to excite two resonance modes. Polarization and spatial diversity techniques are applied to these elements so that the enhanced isolation and reduced coupling effects can be attained. The proposed single antenna element besides 8-element antenna array has been fabricated and experimentally measured. Desirable simulated and measured S-parameters (reflection and transmission coefficients) are obtained for the antenna arrays over the working dual frequency bands. The diversity performance, such as the envelope correlation coefficient (ECC) and diversity gain (DG), has also been simulated and analyzed. Moreover, the performance results, antenna gain and efficiency over the bands, and radiation patterns at the specified resonant frequencies are also presented.

Invariance in duality transformation, the self-dual property, has important applications in electromagnetic engineering. In the present paper, the problem of most general linear and local boundary conditions with self-dual property is studied. Expressing the boundary conditions in terms of a generalized impedance dyadic, the self-dual boundaries fall in two sets depending on symmetry or antisymmetry of the impedance dyadic. Previously known cases are found to appear as special cases of the general theory. Plane-wave reflection from boundaries defined by each of the two cases of self-dual conditions are analyzed and waves matched to the corresponding boundaries are determined. As a numerical example, reflection from a special case, the self-dual EH boundary, is computed for two planes of incidence.

A tri-band Cylindrical Dielectric Resonator Antenna (CDRA) array is proposed for WiFi, wireless LAN, and satellite applications in this paper. CDRA is massively demanded by various smart wireless devices. The claimed antenna array structure is developed and fabricated using an FR4 substrate having relative permittivity (ε_r) of 4.4. Microstrip power divider line is utilised for array excitation. The variation in return loss due to effect of varying micro strip line length, dielectric resonator height and ground plane height has been carefully recorded and presented using parametric study. The array structure is engineered for triple band operations working at 2.4 GHz, 4.1 GHz, and 5.4 GHz frequencies. To achieve adequate bandwidth accompanied by acceptable gain is a very inspiring task. The proposed structure shows a promising maximum impedance bandwidth of 1.14 GHz (40%) and a maximum gain of 9 dBi. The return loss and radiation pattern computed through CST software are verified by practical measurements using VNA device and anechoic chamber atmosphere.

This paper presents a miniaturized frequency selective rasorber (FSR) with both wide absorption and transmission bands. The proposed FSR consists of a resistive sheet and a band-pass frequency-selective surface (FSS) with non-resonant constituting elements. The unit cell structure of the resistive sheet is a meander line loaded with four lumped resistors, which generate a wide absorption band from 2.4 to 6.2 GHz, while the layer of FSS is coupled resonator spatial filter (CRSF) which generates a wide transmission band from 7.5 to 10.2 GHz. Furthermore, there is a 10.5 mm air spacer between the resistive and FSS layers. The period of the FSR structure, which maintains its passband and absorption band performance, is only 10 mm (0.08λL). Simulated and measured results are compared and found to show good agreement.

This letter presents novel composite dual-transmission lines. The proposed line consists of one direct series line and two identical transmission lines connected by a series lumped capacitor. The line is analyzed with an even-odd mode analysis method to have simple closed-form design equations. From the design equations, it is also observed that one can maintain a more realizable value of the impedance of the lines and achieve a good amount of miniaturization by adjusting only the lumped capacitor. To verify this technique, a 74.6% miniaturized Gysel power divider (GPD) is designed at 0.95 GHz compared to reference GPD. The physical size of the proposed GPD is 60 mm × 32 mm (equivalently 0.25λ_g × 0.13λ_g, λ_g is guided wavelength line). Moreover, two transmission zeros (TZs) are obtained near passband which improved the out-of-band performance.

In this paper we investigate a new design of high sensitivity photonic crystal temperature sensor (PCTS). A square lattice of silicon (Si) rods immersed in air matrix is used as a basic structure. The designed sensor consists of two inline quasi-waveguides which are coupled to a resonant cavity (RC). The sensing principle is based on Si refractive index change caused by the variation of the temperatures over a range from 0 to 80˚C. This variation leads to an important shift in the resonance wavelength. The performance of the suggested temperature sensor has been analyzed and studied using finite-difference time domain (FDTD) method. The results show that our designed structure offers a high sensibility of 93, 61 pm/˚C and quality factor of 2506.5. Its structure is very compact with total size 115.422 µm², which is suitable for nanotechnology based sensing applications.

This paper proposes a four-port rectangular monopole antenna for ultra-wideband multiple-input multiple-output (UWB-MIMO) applications. The proposed antenna was designed by using step etching on the ground plane and arrow-shaped slot etching on a radiating patch to enhance bandwidth and improve performances. The homogeneous elements and angular variation techniques were applied to reduce mutual coupling between multiple antenna elements. The structural simulation technique used Computer Simulation Technology (CST) program to analyze the antenna characteristics such as reflection coefficient, group delay, mutual coupling, envelope correlation coefficient, and radiation patterns. The measured results were found to cover a frequency range of 3.1-10.6 GHz for UWB communications. The envelope correlation coefficient for the MIMO system was obtained under 0.001 which is less than the specific parameters of UWB-MIMO antennas. The radiation pattern was bi-directional. Also, the efficiency of the four-port antenna was more than 85.70%.

This article presents a compact size and high isolation 2×2, Multi-Input Multi-Output (MIMO) antenna for Industrial Scientific and Medical (ISM) band and 5G lower frequency band of 5G applications. Mutual coupling has been a great challenge in these applications. To improve isolation between elements of 1×2 MIMO antennas, a mushroom-shaped electromagnetic bandgap (EBG) and a fractal shaped EBG have been investigated. The overall size of the proposed antenna is 38.2×95.94×1.6 mm³ with inter-element spacing (edge to edge) of 0.140λ. The proposed antenna has been designed, simulated, fabricated, and tested. The resulting outcome shows that the antenna operates in the band of 2.43-2.50 GHz and radiates in TM₁₀ mode. By using fractal shaped EBG, isolation of -24.67 dB is achieved. Apart from isolation, other performance parameters of the MIMO antenna are verified. The proposed antenna is suitable for weather radar, surface ship radar, satellite communication, and wireless local area network (WLAN) applications.

We propose and demonstrate the use of radiation pattern measurement method for on-wafer antennas for the first time that is capable of in-depth antenna characterization with limited equipment. This one-antenna method extracts gain without the need for a second antenna in the on-wafer probe station environment. A combination of reference reflector translation and rotation allows radiation pattern sampling at multiple angles enabling characterization over the relevant solid angle. Several microstrip patch antennas with varying beam directions (0˚, 20˚, and 30˚) were measured with the proposed method over 120˚ in the H-plane with good agreement between simulation and experiment. The method offers a cost-effective and time-efficient solution for probe-fed, on-wafer antenna radiation performance characterization.

Electromagnetic Band Gap (EBG) structures can be employed near the feed line of a UWB monopole antenna, to reject the already existing narrowband radio signals operating within the spectrum of an Ultra Wide Band (UWB) antenna. Multiple EBG structures are required to reject multiple interfering bands. However, since the ground plane of a monopole antenna is limited, there is a need for compact EBG structures. This paper presents the application of a Two Via Slot (TVS) EBG to reject the interfering upper Wireless Local Area (WLAN) band (5.725 GHz-5.825 GHz) from the spectrum of a fork-shaped UWB monopole antenna. The simulated results demonstrate that the TVS EBG gives better performance in terms of higher and sharper Voltage Standing Wave Ratio (VSWR) value at the rejection band while occupying least ground plane area than Conventional Mushroom Type (CMT) EBG, Edge Located Via (ELV) EBG, slotted-patch ELV EBG, and semi-circular EBG. The proposed design is fabricated and measured. The measurement results prove that the antenna successfully achieves wide impedance bandwidth from 3 GHz to 12 GHz while rejecting the frequencies from 5.4 GHz to 5.9 GHz.

This paper presents the design of an 8-element linear array for Adaptive Antenna applications using the Least Mean Square (LMS) algorithm towards improving the directive gain, beam steering capabilities, half-power beamwidth, sidelobe level, and bandwidth of array. A conventional patch antenna is optimized to operate at 3.6 GHz (5G applications) with two symmetrical slots and Quarter Wave Transformer for feeding, and this design is extended up to 8 elements using CST Microwave Studio parameterization. The Return Loss (S₁₁), Directivity, HPBW and VSWR of the antenna array are observed for the 2, 4, and 8 element adaptive array. The inter-element spacing for resulting eight-element antenna array geometry is optimized to obtain maximum directive gain. This geometry appears promising in improving the directive gain from 7.6 dBi to 15.1 dBi for a single element to eight elements respectively. Further, the LMS algorithm is used to compute the optimal complex weights, considering different angles for the desired User (+45˚ and -45˚) and Interferer (+20˚ and -20˚) during MATLAB simulation, and then these optimal weights are fed to antenna elements using CST for beam steering in a different direction. Maximas in the direction of user and nulls in the direction of interferer are obtained using CST software and found closely matching with MATLAB results.

Ultra-reliable and low-power wireless communications are desirable for wireless networking in extreme environments such as underground tunnels, underwater, and soil. Existing wireless technologies using electromagnetic (EM) waves suffer from unpredictable multipath fading and blockage. The recent development of magnetic induction (MI) communication provides a low-power and reliable solution, which demonstrates negligible multipath fading, high penetration efficiency, and low attenuation loss in lossy media. However, existing works neglect the fact that MI communication only demonstrates such advantages in the near-field, beyond which the MI communication converges to electromagnetic wave-based communication and all the aforementioned advantages disappear. This letter develops a magnetic field propagation model to show MI communication's different performances in the near-field and the far-field. We develop rigorous models to capture the multipath fading, the penetration efficiency through inhomogeneous media, and the attenuation loss in lossy media. The results show that although MI communication can provide reasonable signals in the far-field, it only demonstrates negligible multipath fading, high penetration efficiency, and low attenuation loss in the near-field.

A stub-loaded stepped-impedance resonator (SLSIR) is proposed. Its input impedance is derived, and its resonant conditions are found. First order and second order triband bandstop filters (BSFs) are designed using this resonator. Simulations on both filters show that they generate three attenuation poles at 0.5, 1.2, and 2.1 GHz. The second order filter is also fabricated and characterized using a microwave vector network analyzer. Simulation and measurement results on the second order filter show good correlation.