In this paper, a hybrid antenna array for 4G/5G smartphone applications is presented. The hybrid antenna system is composed of one array of two antenna elements for 4G application and another array of six antenna elements for 5G application. By loading PIN diodes and changing the on/off state of the PIN switch, then the resonance point will shift. The 2-antenna array broadens the bandwidth of 4G frequency band and is capable of covering GSM850/900/DCS1800/PCS1900/UMTS2100 and LTE2300/2500 operating bands. A U-shape monopole strip and an S-shape slot coupling technologies are also introduced, the 6-antenna array improves the impedance matching for the proposed 5G antenna array, and is capable of covering the 5G (3300 3600 MHz and 4800 5000 MHz), which can meet the demand of 5G application. Spatial and polarization diversity techniques are implemented on these antenna elements so that high isolation can be achieved. This hybrid antenna array is fabricated, and typically experimental results such as S11, isolation, radiation pattern, efficiency, and channel capacity are presented. The measured results are in good agreement with the simulated ones.

In this article, a modified circular shape printed dipole structure is studied to achieve wide bandwidth and dual-band circular polarization (CP) behavior along with dual polarizations. The idea behind this structure is that asymmetric geometry can give rise to circular polarization with an optimized position of coaxial probe feed. The circular patches on both sides of the substrate are altered with elliptical slots at an optimized location in association with opening slots. With these alterations the impedance bandwidth for S₁₁<-10 dB is ranging from 2.36-7.34 GHz (4.97 GHz) which is nearly 102.5% about mid-point frequency 4.85 GHz. The antenna resonates at a lower band (1.55 GHz) and shows linear polarization (LP) operation at that band whereas dual CP bands with dual senses are obtained at higher frequency ranges 4.00-4.60 GHz and 6.07-7.13 GHz respectively with 3-dB axial ratio bandwidth of 13.7% and 16.6%. The simulated and measured experimental results are in close agreement. This antenna is suitable to be used for navigation purposes, radar communication, and wireless communication (especially wireless avionics intra communications) in S and C bands, respectively.

First of all we inform the audiences that this article is a Review Paper (RP) for the PIERS17 Proceedings Paper (Zheng et al. [17]). The reason why we publish this RP is that: although the paper [17] reported important ideas and simulation facts, details of the contents were insufficient, and the audiences of the report were not satisfied. This was because the page number was limited, and we saved the number of pages. However, because the contents of~[17] are important, we decided to publish an RP, which would provide additional explanations or give considerations supporting main issues. Now, we start the abstract from Section~1. Here, we mention historical topics and RP-related things. In Section~2, we explain the problem of diffraction by a conically-mounted metal grating. To save the page number, we skip the method of solution. In Section~3, we explain our method in noise free case. We show the high precision of the quadratic (or parabola) approximation. We define the workspace (WS: relation between index range of a sample and a proper azimuth angle) and one-to-one correspondence between sample index and resonance angle. In Section~4, we try our method in a noisy environments. A curve-fitting procedure and three types of noise filters work to find satisfactory solutions. That is, in both 3. and 4., the resolution of the index is 7-digit usually, which is our target from the beginning. We think that the introduction of AI or statistical processing would increase the stability of the result. In Section~5, we mention some of future works. In APPENDIX A, we explain the method: How to find the azimuth angle, which we need in solving the diffraction problems by conically-mounted grating.

An eleven element log-periodic dipole-array (LPDA) antenna, occupying a surface area of only 90 x 52 mm², printed on an ultra-thin flexible Kapton substrate of thickness 0.035 mm , is proposed. The antenna operates with a stricter 10 dB reflection coefficient bound in the frequency bands 2.75-3.53 GHz and 4-6.2 GHz. For a less stringent bound of 6 dB (which is acceptable for wearable applications), it operates in the wider range of 2.7-6.8 GHz. The antenna has an end-fire radiation pattern with a maximum measured gain of 6 dBi. The flexibility of the antenna is illustrated by reflection and radiation pattern measurements for three different radii, i.e., 50, 30, and 10 mm in both the convex and concave configurations. It is experimentally demonstrated that LPDA exhibits stable input-impedance characteristics and consistent radiation properties over the whole operating band under all bending conditions. The low cost, light weight, and flexible design, as well as the broadband performance in both concave and convex bent configurations, prove the suitability of the antenna for the contemporary flexible electronic devices.

In this paper, a novel zeroth-order resonator (ZOR) antenna by exciting two asymmetric coplanar strips (ACS) is reported. In order to attain ZOR resonance, the antenna has resorted to two annular ring resonators (ARRs) which control antenna characteristics at 2.7 GHz. In this frequency, antenna treats such as a planar dipole antenna with omnidirectional patterns and linear polarization. The proposed antenna by utilizing two ports can change circular polarization diversity at the second band region. The proposed miniaturized antenna covering more than 80% bandwidth overall two bands and a more than -15 dB isolation between two input ports can be used in portable systems.

A novel, miniature multiple input multiple output (MIMO) ultra wide band (UWB) antenna with dual notched characteristics is proposed. The antenna incorporates a tapered microstrip feed line with two radiating patch structures procured by the incorporation of two ellipses with a circle and a reduced ground structure. The proposed antenna is printed on an FR-4 substrate having a concise size of 40 x 22 mm² to cover -10 dB bandwidth of 3.18-11.26 GHz with fractional bandwidth of 112%. The two notched bands 3.31-3.99 GHz for WiMAX and 4.97-5.93 GHz for WLAN accomplished by two T-shaped parasitic structures are etched above ground plane and inverted U- shaped slots etched on radiating patch, respectively. The isolation of < -15 dB is realized by inserting a T-shaped stub in between two patch elements. The measured MIMO diversity characteristics are the evidence of that the proposed antenna is appropriate for portable wireless applications.

In recent years, surface magnetic resonance tomography (MRT), which is applied to the direct determination of the presence of groundwater, has been developed from underground two-dimensional to three-dimensional (3D) imaging. However, because of the influence of subsurface electrical conductivity, the magnetic resonance sounding (MRS) signal has been proved to be a complex-valued form. Moreover, the real and imaginary parts of MRS signals show different sensitivities to aquifers of different depths. In this study, a complex model of 3D MRT with separated loops configuration is introduced to provide accurate water-bearing imaging. Through simulation experiments, we demonstrate that the separated loops configuration is conducive to obtaining the imaginary part signal of MRS. Compared with a conventional model, the complex model has better 3D imaging resolution and sensitivity, especially for the deep regions. Moreover, in the case of noise interference and the presence of a multi-aquifer, the imaging results of complex inversion are reliable. As a result, this study is significant to the further development of multi-channel MRS instruments and provides a feasible method for high-precision imaging.

The objective of this paper is to propose an inversion model of soil moisture using a neural network, and compare the performance of this method with two empirical models in soil moisture inversion. A wide dataset of backscattering coefficients extracted from Sentinel-1 images and in situ soil surface parameter measurements (moisture content and roughness) are used. Since the available backscattering models have limited performances of describing the nonlinear relationship between soil parameters and backscatter coefficient, the retrieval of soil parameters from radar backscattering coefficient remains challenging. The proposed inversion method of a neural network is used for establishing this relationship. At the same time, two empirical models are employed to estimate the soil moisture for comparison. The results show that for most of the six measuring stations the inverted soil moisture with the neural network model has higher correlation coefficient with the in-situ soil moisture than those by the empirical models. Moreover, the neural network model inversion results under multi-polarization input conditions are discussed in this paper. The results of stations 2, 4, and 5 show that R² of multi-polarization inputs are increased by 0.1928, 0.4821, and 0.2758 respectively, compared with those of single-polarization inputs.

Space-time adaptive antijamming problem has received significant attention recently for global navigation satellite system (GNSS). It can jointly utilize spatial filters and temporal filters to suppress interference signals. However, most of the works on space-time antijamming problem presented in the literature require a space-time two-dimension (2-D) array with multiple antennas and delay taps. In this paper, an effective adaptive antijamming method based on space-time a 2-D sparse array is proposed. The maximum array gain is utilized to construct a space-time 2-D sparse array. The space-time antijamming weight vector is given by minimizing the 2-D sparse array output power. Compared with the previous works, the presented method can have better antijamming performance than a space-time 2-D uniform array. Simulation results verify the effectiveness and feasibility of the proposed method.

This work presents a novel semi-analytical model for magnetic field calculation in a high-speed surface-mounted permanent-magnet machine with conducting and permeable retaining sleeve. The retaining sleeve with conducting material and non-homogeneous permeability affects the machine electromagnetic performance by altering main flux inductance and developed torque profile. This performance deviation can be attributed to eddy-current reaction field and saturation, the latter occurring due to pole-to-pole leakage flux. Saturation is modeled with a space-varying relative permeability, expressed as a Fourier series. Eddy currents are evaluated with an auxiliary winding, defined as a surface current density in the conducting region. The proposed method is based on well-established Maxwell-Fourier method. This permits other analysis, such as slotting effect through subdomain technique. The assumptions considered for the developed semi-analytical solution in two-dimensional problem are presented in depth and confronted with finite-element method results, confirming validity of proposed methodology.

In this paper, a reconfigurable patch antenna with Circular Polarization (CP) diversity with theoretical discussion and verification is proposed for the fifth generation (5G) of mobile communication systems. The proposed antenna contains two PIN diodes, which are correctly placed on the ground plane to attain polarization diversity. By switching between two ON/OFF modes in the PIN diodes, the proposed antenna can support the RHCP mode or the LHCP mode. An antenna with the well-matched impedance bandwidths (S₁₁ ≤ -10 dB) of 2.5 GHz (27~29.5 GHz) and 3 GHz (36~39 GHz) and the dual-band 3-dB axial ratios of 6% (27.3-29 GHz) and 8.4% (35-38.2 GHz) operates at both the RHCP and LHCP modes. The experimental result shows that the proposed antenna has a circular polarization bandwidth at the center frequencies of 28 and 38 GHz for both the RHCP and LHCP.

A compact wideband bandpass filter (BPF) with stopband suppression by utilizing transversal signal interaction concepts is proposed in this article. Two transmission paths from Port I to Port II are separately constructed by multi-mode step impedance resonator (SIR) and shorted coupled lines. The proposed configuration generates two controllable transmission poles, and wideband characteristic can be realized. Moreover, multiple transmission zeros are implemented by signals superposition of two transmission paths and stub loaded fans resulting in steepness sideband and broad upper stopband suppression up to 100 GHz. For clarification, the designed wideband centered at 4.5 GHz with fractional bandwidth of 14.2% is designed, assembled and measured. The circuit size of prototype BPF only occupies 0.94 cm², and the presented BPF is evaluated by test results and simulated predictions with good agreement.

In this paper, the application of gammadion chiral metamaterial for converting linearly polarized waves to circularly polarized waves is presented and using this a circular polarized antenna for wireless application is proposed. First of all, a traditional rectangular microstrip patch antenna has been designed at resonance frequency of 5.15 GHz, which gives linear polarization. The linearly polarized waves are allowed to feed gammadion chiral metamaterial, which is placed at a height of 33 mm above the reference antenna. The gammadion chiral metamaterial produces two special effects that are responsible for polarization rotation: circular dichroism and optical activity. As a result of these effects, the necessary conditions for circularly polarized radiation are fulfilled, and antenna is converted to the circularly polarized antenna. This method gets rid of designing of complicated feeding structure that is necessary for circular polarization. The role of gammadion chiral metamaterial to convert linear polarization to circular polarization has been described. The antenna is fabricated, and the measurement of return loss, axial ratio, etc. is also carried out. Simulation and measurement results agree with each other.

An auxiliary antenna array scheme for sidelobe interference cancellation of satellite communication system is proposed in this paper. Considering earth curvature, signal bandwidth and transmission loss, a precise model of satellite communication interference scenario is established. In order to improve anti-interference capability, the performance of the auxiliary antenna array is studied by the minimum mean square error (MMSE) criterion. Then, a 7-unit linear microstrip antenna array is manufactured as the auxiliary antenna array. The main contribution of this paper is the corresponding auxiliary antenna array analysis and design. Simulated and experimental results confirm that the proposed scheme can achieve a relatively high interference cancellation radio (ICR) of about 25 dB in a wide beam range.

An approach towards beamforming for a uniform linear array (ULA) based on a novel optimization algorithm, designated as Fibonacci branch search (FBS) is presented in this paper. The proposed FBS search strategy was inspired from Fibonacci sequence principle and uses a fundamental branch structure and interactive searching rules to obtain the global optimal solution in the search space. The structure of FBS is established by two types of multidimensional points on the basis of shortening fraction formed by the Fibonacci sequence, and in this mode, interactive global searching and local optimization rules are implemented alternately to reach global optima, avoiding stagnating in local optimum. At the same time, the rigorous mathematical proof for the accessibility and convergence of FBS towards the global optimum is presented to further verify the validity of our theory and support our claim.Taking advantage of the global search ability and high convergence rate of this technique, a robust adaptive beamformer technique is also constructed here by FBS as a real time implementation to improve the beamforming performance by preventing the loss of optimal trajectory. The performance of the FBS is compared with five typical heuristic optimization algorithms, and the reported simulation results demonstrate the superiority of the proposed FBS algorithm in locating the optimal solution with higher precision and reveal the further improvement in adaptive beamforming performance.

A dual-band microstrip rectenna for wireless local area network (WLAN) applications is presented. It consists of a dual-band dual-polarized receiving antenna and a dual-band high efficiency rectifier. The receiving antenna includes a circular loop, a coplanar waveguide (CPW), and a microstrip line. To minimize mutual interference and ensure high isolation of more than 20 dB between the dual-polarized ports, a CPW is used to produce vertical polarization modes and the horizontal polarization modes is fed by a microstrip line. The horizontal excitation port is used for information receiving, while the vertical feeding port transfers enough wireless energy for rectifying. A co-simulation of HFSS and ADS is used for analysing the performance of rectenna. Measured results show that it has the -10 dB reflection coefficient bandwidths of 510 MHz (2.39-3.09 GHz) and 920 MHz (5.16-6.08 GHz) for rectifying Port 1, where the isolation between the ports is higher than 25 dB, and the cross polarization is less than -15 dB in two bands. The maximum microwave-direct current (mw-dc) conversion efficiencies of 67.7% and 57.03% at 2.45 GHz and 5.8 GHz are achieved with a 300 Ω load and 16 dBm receiving power.

The paper is devoted to the investigation of radiation frequencies characteristics of a modified waveguide aperture by wire media (WM). Such construction allows radiating weak electromagnetic (EM) waves --- the frequencies of which are non-corresponding to the resonant ones of the modified radiator. It is possible due to the unusual properties of metamaterials, namely the negative value of permittivity of WM. The simulation studying shows that the changing of value of wires radius and at the same time the value of filling factor impacts on the radiation frequency. Therefore, the increase of filling factor leads to the increase of the resonance frequency. The radiation is narrowband with S₁₁-parameter less than -20 dB. The experimental investigation shows that the decrease of the value of lattice period allows increase of the width of radiation frequency range from 30-40 MHz up to approximately 80 MHz at the level of 0.3 (≈ -10 dB). At the same time, the increase of wires' radius values leads to the increase of the value of resonant frequency. Finally, the experimental study demonstrates that the value of overlap between waveguide port (source of EM waves) and wire media sample negligibly impacts on the resonance frequency values and operational range for D/L = 0...0.3.

In this paper, the thermal degradation of electro-conductive fabrics exposed to high current impulses is studied by using an equivalent resistive circuit and a technique commonly applied to the analysis of exploding wires. A method to estimate the threshold burst current of conductive fabrics is derived based on the so-called specific action, which is defined as the integral of the squared current density over the time applied at critical locations of the fabric such as the contact areas between yarns. The model has been experimentally validated on woven and non-woven fabrics using lightning impulse currents applied to the conductive fabrics coated with Cu-Ni alloy. A general rule for determining the dimensions of conductive fabrics as a function of the input-current specific-energy levels has also been derived.

This paper proposes a novel miniaturized UWB bandpass filter by cascading two miniaturized low-pass and high-pass modules. On account of the slow wave and stopband characteristic of defected microstrip structure (DMS), an E-shaped DMS with low-pass characteristic is presented, and an RLC equivalent circuit is utilized to analyze it. By three-dimensional electromagnetic modeling , the S parameters can be obtained to extract the initial parameter values of the RLC equivalent circuit and verify the validity of equivalent circuit in Advanced Design System. The high-pass module uses a lump element to reduce the circuit dimension. The high frequency selectivity can be achieved by loading L-shaped stubs, which produces one transmission zero at the upper band of passband and has a good rectangle coefficient of 1.2 (25 dB-bandwidth/3 dB-bandwidth). To verify the idea, a compact UWB bandpass filter is simulated and fabricated. The result shows that the passband range is 3.1-10.6 GHz with 1 dB loss, and the measurement has a good agreement with the simulation. Besides, a notched wave working in X wave band can also be generated. Compared with the previous works, this UWB bandpass filter has the advantages of miniature and high selectivity.

A new hybrid double stator bearingless switched reluctance motor (HDSBSRM) realizes the decoupling of torque and suspension force from the structure, and the permanent magnet added in the inner stator further reduces the suspension power loss. For HDSBSRM, loss is the main cause of temperature rise. In order to ensure the stable suspension and rotation of the motor, loss of the Magnetic Bearing (MB) and motor are calculated and analyzed by finite element method (FEM). Based on the loss result, the temperature field is analyzed. The analysis of loss and temperature field provides important theoretical basis for the design of motor cooling system.