This research work introduces a compact dual composite right/left handed (D-CRLH) unit cell structure for filtering power divider (FPD) application. The D-CRLH unit-cell consists of an interdigital capacitor with two shorted fingers in series. It contains a meander line, a rectangular stub, and a via in shunt, both series and shunt elements provide filtering response as a bandpass filter. This design has been developed on dielectric material of thickness 1.6 mm, usually called as Epoxy glass substrate (FR-4). The transmission line of length λ_g/4 of a Wilkinson power divider has been replaced with a D-CRLH unit cell to reduce the size of proposed structure more than 60%. Another advantage of using a D-CRLH structure is the position of resonance frequency independently controlled by series parameter only because of shorted structure. The series chip resistor has been utilized to improve the isolation at resonance in between output ports. It offers miniaturization with electrical footprint area of 0.15λ_g x 0.27λ_g (11.4 mm x 20.4 mm), here λ_g represents the guided wavelength at resonance frequency of 2.5 GHz.

The multilevel fast physical optics (MLFPO) is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers. This method is based on the quadratic patch subdivision and the multilevel technology. First, the quadratic patches are employed rather than the planar patches to discretize the considered scatterer. Hence, the number of the contributing patches is cut dramatically, thus making the workload of the MLFPO method much lower than that of the traditional Gordon's method. Next, the multilevel technology is introduced in this work to avoid calculating the physical optics scattered fields from the considered scatterer directly, so that the proposed algorithm can significantly reduce the computational complexity. Finally, numerical results have demonstrated the accuracy and efficiency of the MLFPO method based on the quadratic patches.

It becomes more and more challenging to satisfy the long-term demand of transmission capacity in wireless networks if we limit our research within the frame of traditional electromagnetic wave characteristics (e.g., frequency, amplitude, phase and polarization). The potential of orbital angular momentum (OAM) for unleashing new capacity in the severely congested spectrum of commercial communication systems is generating great interest in wireless communication field. The OAM vortex wave/beam has different topological charges, which are orthogonal to each other. It provides a new way for multiplexing in wireless communications. Electromagnetic wave or synthetic beam carrying OAM has a spiral wavefront phase structure, which may provide a new degree of freedom or better orthogonality in spatial domain. In this paper, we introduce the fundamental theory of OAM. Then, OAM generation and reception methods are equally demonstrated. Furthermore, we present the latest development of OAM in wireless communication. We further discuss the controversial topic ``whether OAM provides a new degree of freedom'' and illustrate our views on the relationship between OAM and MIMO. Finally, we suggest some open research directions of OAM.

A new metasurface (MS) structure for wideband low radar cross section (RCS) and its performance as an antenna has been analyzed and proposed in this paper. The MS has been designed with two different AMC unit cells, and the novel AMCs scatter the incident waves diffusively. The parameters and dimensions of the AMCs are optimized to get the best performance of the antenna. Furthermore, the unit cell structure of metasurface is designed and positioned to improve the directivity of the antenna. The reflected electromagnetic waves scatter in a manner of 180⁰ out of phase with the incident waves, and the antenna's scattering and radiation performance has also been examined. Full-wave simulations and measurements confirm that the proposed antenna achieves 10 dB RCS reduction over a wide bandwidth of 3-12 GHz (61.2%). A monostatic peak RCS reduction of 45 dB is accomplished at 5 GHz, 7 GHz, and 11.5 GHz. Besides, the radiation characteristics of the antenna are appropriate in the boresight direction, and the antenna exhibits good performance in $E$-, $H$-planes and ensures adequate directivity.

In the iterative solution of the matrix equation arising from the multilevel fast multipole algorithm (MLFMA), sparse approximate inverse (SAI) preconditioner is widely employed to improve convergence property. In this paper, based on the geometric information of nearby basis functions pairs and finer octree grouping scheme, a new sparse pattern selecting strategy for SAI is proposed to enhance robustness and efficiency. Compared to the conventional selecting strategies, the proposed strategy has only one variable parameter instructing the constructing time and memory usage, which is more user friendly. Numerical results show that the proposed strategy can make use of the non-zero entries of near-field matrix in MLFMA more effectively and elaborately without compromising the numerical accuracy and the natural parallelization of SAI.

This paper presents a novel compact printed antenna exploitable for Dedicated Short-Range Communication at 5.8 GHz. The design of the proposed device is based on the concentric arrangement of two contemporary fed patches operating with different modes. The resulting antenna exhibits a fan-beam pattern, with a wide lobe in one plane and narrow lobe in the plane perpendicular to the former, while retaining exceptionally small dimensions. The actual width of the beam makes the antenna suitable to cover a single road lane, as prescribed by the Intelligent Transportation System framework requirements. Furthermore, it natively operates in Circular Polarization, as prescribed by the ETSI EN 302 663 normative. Experimental validations demonstrate that the proposed antenna presents a Left-Hand gain of 4.1 dB at center frequency, with HPBW_x and HPBW_y equal to 160˚ and 45˚, respectively, showing good agreement with the simulations. This measured performance confirms that the device is adequate to cover a single road-lane, according to the European framework for Dedicated Short-Range Communication for traffic monitoring.

Magnetic materials are found naturally in certain terrestrial and extra-terrestrial geological settings and can influence subsurface mapping and fluid transport and content estimations. With the advent of magnetic nanoparticle research there is also the possibility that these will be inputted in the environment on purpose, as research and industrial applications, or inadvertently as contaminants. The presence of magnetic materials is usually not considered in electromagnetic response modeling of saturated or partially saturated porous materials. This is because relative magnetic permeability of most natural materials is close to one, and thus should not affect propagation velocity calculations. The objective of this study was to investigate the effect of magnetic mineral inclusions on the velocity of propagation of an electromagnetic signal on porous materials saturated with water and its influence on volumetric water content estimation. The effective relative dielectric permittivity and magnetic permeability terms were modeled using Maxwell-Garnett, Polder-van Santen, Lichtenecker and Looyenga effective medium approximation equations. Data from three nonmagnetic soils saturated with water to varying degrees was used for preliminary model evaluations. The effect of magnetic minerals was tested by mixing magnetic sand with quartz sand at different proportions and measuring propagation velocity under fully water saturated conditions using Time Domain Reflectometry (TDR). Propagation velocity decreased with increasing magnetic volume fraction, while the effect of increasing magnetic fraction on attenuation factor was not markedly distinct. Water content estimations using models not accounting for magnetic inclusion substantially overestimated volumetric water content in saturated porous media.

Scattering of homogeneous plane waves by a Perfect Electric Conductor half-plane in uniform rectilinear motion in a simple lossless medium is investigated using Wiener-Hopf Technique in the context of Hertzian Electrodynamics. The cases of motion being parallel and perpendicular to the plane are tackled separately. Restrictions on incidence angle vs. speed for the realization of scattering phenomena are investigated in each case. Parallel motion mode reveals the possibility of excitation of surface waves upon reflection, which also contribute to edge diffraction mechanism. Numerical results are illustrated and discussed for scattered fields. Comparative theoretical results for the solution of the same problem using Special Relativity Theory are provided and discussed.

A traditional magnetic resonant coupling wireless power transfer (MRC-WPT) system is highly sensitive to the distance between transmitting and receiving coils. The transfer performance deteriorates at short distance due to magnetic over-coupling and magnetic weak-coupling at long distance which also results in the decrease of power. In order to improve the power transfer ability, this paper presents an MRC-WPT system with a novel design of resonant loops. Unlike the conventional system in which the receiving coil is identical with the transmitting coil, the receiving coil in the proposed system is different from the transmitting coil in terms of distance between turns. Theoretical equivalent models are presented to investigate the impact of the mutual inductance on the transfer efficiency. Based on numerical simulation, it is found that relatively more uniform mutual inductance can be obtained with the proposed resonant loops. With the proposed MRC-WPT system, the results show that the power transfer ability at short and long distances is improved. The average transfer efficiency is enhanced about 10% compared with the conventional system. Furthermore, the sensitivity of the proposed MRC-WPT system to lateral and angular misalignments is studied and compared with the conventional system. An experimental prototype of the proposed MRC-WPT system is designed for validation. The results show that the performance of the proposed MRC-WPT system outperforms the conventional system without adding any complicated control circuits.

The loss of magnetic bearing in the process of operation will lead to the temperature rise of the bearing and affect its performance. A permanent magnet is used to provide bias magnetic flux for hybrid magnetic bearing, which can reduce the loss and temperature rise of the magnetic bearing. In this paper, the loss of radial 2-DOF hybrid magnetic bearing (HMB) is analyzed. On this basis, the 3D thermal analysis model of HMB is constructed by using ANSYS Workbench finite element software. The loss is introduced into the temperature field as a heat source, and the temperature distribution of magnetic bearing is calculated. Combined with the results of loss and temperature analysis, the structural parameters were optimized by using genetic particle swarm optimization algorithm (GAPSO). The results show that the loss and temperature rise of the optimized magnetic bearing are significantly reduced.

Synthetic aperture interferometric radiometer (SAIR) is a high-resolution passive imager by sparsely arranging a number of small aperture antennas to synthesize a large aperture. However, the SAIR requires as many receivers as antennas needed, which results in high system complexity and hardware cost and limits the application of the SAIR. Aiming to reduce the system complexity of SAIR, a new passive coding imaging method is proposed in this paper. By using a new aperture coded measurement approach, the proposed method can significantly reduce the number of RF chains while keeping the image fidelity. The effectiveness of the proposed imaging method has been varified by simulations. The results reveal that the proposed method can be an efficient alternative for simplifying the architectures of SAIR.

The aim of this paper was to propose and design a photonic crystal drop filter based on ring resonators and study its properties numerically. This structure is constituted in a two-dimensional square lattice. The resonant wavelengths of the PCRR proposed are λ = 1.553 μm, and the extraction efficiency exceeds 99% with a quality factor of 5177. To study the all-optical OR and XOR logic gate function, we calculated the electric field distribution of the 2D photonic crystal for the 1.553 μm signal light. In order to have a large selectivity of filtering and also of having a fast switching in the field of nonlinearity, we increase the number of ring resonators, and the latter are used for designing all optical logic gates which work using the Kerr effect equal to 10^-6 m²/w.

The paper aims at studying the shielding effectiveness of a closed cylindrical surface simulated by N dielectric coated conducting strips. The far fields of an electric line source in the presence of the simulated surface and in the absence of the surface were calculated, and the ratio between them represents the shielding effectiveness produced around the surface. The solution of the problem was developed based on full wave analysis. In which all fields are represented in terms of infinite series of Mathieu functions. The addition theorem of Mathieu function was employed to facilitate the application of boundary condition. Computer program was developed based on the resulting formulations to produce numerical values. Numerical results are presented for circular and square cross-sectional cylindrical surfaces. Comparison with the published data for the radiation from slotted circular cylinder showed excellent agreement. Other useful results for shielding effectiveness are furnished.

Design of a harmonically tuned RF Power Amplifier (PA) with enhanced efficiency and gain is presented in this letter. It makes use of a tri-band impedance transformer as a two-port output network for facilitating concurrent optimum fundamental and harmonic impedances at the drain terminal. The design is augmented by analytical formulations and analysis to identify the optimal impedance matching scenario at the fundamental, second harmonic, and third harmonic. A thorough analysis reveals that the proposed PA design scheme is very simple while maintaining the performance obtained from the load-pull. A prototype operating at a frequency of 3.5 GHz is developed on RO5880 using 10W GaN HEMT. An excellent agreement between the measured and the EM simulated results validates the proposed design technique.

An antenna array formed by four PIFA elements located very close to each other, with low inter-element matching for MIMO applications is proposed. The antenna array consists of four F-inverted wideband radiators, with a fractional bandwidth around 56%, spaced one to each other by a very short distance (< 0.065 λ0) at a centre frequency of 2.55 GHz. The operational bandwidth goes from 1.88 to 3.15 GHz considering the Sii < -10 dB at each port. Moreover, the coupling among ports reaches values below Sij < -10 dB and getting values less than -30 dB at 1.8 GHz, just by employing an uncomplicated technique implemented by a neutralization line between elements. The antenna array gain goes from 2 dB to 6 dB over the operating bandwidth. Concerning MIMO figures of merit, the radiation pattern of each element is orthogonal to each other. The Envelope Correlation Coefficient is below 0.04 at the designed frequency, reaching a peak around 0.082 at 1.8 GHz, but still achieving the requirement for MIMO operation (less than 0.5). The Total Active Reflection Coefficient (TARC) is almost convergent at the design frequency, showing low dependence on random signals at different elements, and finally, the diversity gain reaches values close to 20 dB, making the array suitable for MIMO access point applications.

High Impedance Textured Substrate is presented for suppression of Surface Waves in Microstrip Antennas. Surface wave propagation limits the radiation efficiency, bandwidth, gain, alters the main beam radiation pattern and increases side lobe levels as well as the back lobes. A novel technique to suppress the surface waves with periodic arrangement of metallic cylindrical pins embedded in the substrate except the area underneath the radiating microstrip patch is presented here. Two structures with solid as well as hollow cylindrical pins are analysed with Spectral Domain Analysis. The textured pin bed structure creates negative permittivity and high capacitive impedance and thus suppresses the propagation of TM-surface waves. The gain of 11.83 dB with an enhancement of 6dB over normal microstrip patch antenna is achieved. Further an increase of 1.61 dB gain with 12.27% improvement in radiation bandwidth is observed in the antenna structure with hollow cylindrical pins as compared to that of solid cylindrical pins. A uniform gain of more than 11 dB is achieved with a percentage bandwidth of 17.43%.

In this paper, a dual-band Multiple Input Multiple Output (MIMO) antenna for fifth-generation (5G) band (3.3-3.6 GHz and 4.8-5.0 GHz) is presented. The proposed MIMO antenna fed by coplanar waveguide (CPW) contains two symmetric antenna elements with two inverted L-shaped stubs. High isolation is successfully acquired by adopting a double-Y-shaped stub and partial ground plane. To obtain compactness, the antenna printed on an FR4 substrate has two triangle corners cut off. To study the performance, the antenna is simulated by Ansoft HFSS 13.0, and then fabricated and tested. The measurement results demonstrate that the antenna has achieved impedance bandwidths (S₁₁ < -10 dB) of 790 MHz (3.08-3.87 GHz) and 880 MHz (4.7-5.58 GHz) with fractional bandwidths of 22.7% and 15.8% respectively, which covers 3.45/4.9 GHz 5G bands. Meanwhile, the measurement results exhibit an enhanced isolation more than 20 dB, a low envelope correlation coefficient (ECC) below 0.001, an average gain better than 2 dB and a stable radiation pattern within operation bands. In addition, the parameters including efficiency, DG, CCL, MEG and TARC are also analysed. The simulated and measured results indicate that the proposed MIMO antenna can be applied to 5G communication system.

A dual-band antenna operating in dual bands is presented. The antenna is composed of two substrate layers covered with three printed patch layers. The top layer is an electrically small ring; the middle consists of four spiral resonators (SRs); and the bottom is a split-ring resonator (SRR). Inductive couplings between layers change the radiation Q factor of the original ring antenna and promote resonating modes in UHF and S bands. Besides, the input matching property is also improved. The measured return loss agrees well with the calculated results, and the radiation patterns are also presented. From experiments it is found that the proposed antenna is electrically small at operation dual-bands.

For a radiating structure such as dipole/patch array mounted on an aerospace platform, the radiation mode radar cross section (RCS) plays a significant role compared to the structural mode RCS. Thus the estimation and control of array RCS without degrading its radiating characteristics poses a challenge for an antenna engineer. In this paper, a novel design of a low profile 4-element patch array with hybrid HIS-based ground plane is presented to demonstrate both in-band and out-of-band structural RCS reductions. A significant broadband reduction in structural RCS has been achieved from 1 GHz to 80 GHz. The radiation mode RCS of the patch array is computed and controlled through optimized design parameters without degrading the radiation characteristics. The computed array RCS shows that even radiation mode RCS can be reduced except in operating frequency range.

A triple-section arm structure is proposed for designing a planar spiral antenna. All three sections are designed by combining logarithmic, rooted, and sine equations. The slowly outstretched and contractive structure is innovatively realized. According to the radiation characteristics of the spiral antenna, each section corresponds to different in-band enhancement effects. Numerical simulation in the frequency domain and experiments using two different baluns are carried out. The results show that the novel spiral topology could simultaneously achieve improved axial ratio, low cross-polarized gain, and excellent impedance matching throughout the whole band. The axial ratio is reduced by 1.5 dB at mid frequencies and more at low frequencies, comparing the proposed arm with a sinusoid-added equiangular spiral arm. Without applying the resistive loading method, a lower cut-off frequency of 750 MHz is still realized both in impedance bandwidth and axial ratio bandwidth. The low cut-off frequency of the proposed arm is 30.2% lower than the conventional Equiangular spiral arm. Besides, the polarization isolation is significantly improved, especially at low frequencies. Therefore, the proposed miniaturized spiral arm structure could be a competitive form for designing spiral antennas.