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.

This paper proposes and demonstrates a compact integrated filtering antenna built on a square ring resonator coupled with a capacitors loaded microstrip line filter. A microstrip filter module is connected to feeding line of the conventional patch without adding extra space. Thus, the combined configuration possesses radiating and filtering functions simultaneously. The proposed filtenna has a fractional bandwidth (FBW) of 3% at center frequency 2.4 GHz with 2.5 dB of maximum gain. The obtained result shows that the proposed design shows good stopband gain rejection, good selectivity at band edges, and smooth passband gain. Furthermore, the introduced filtenna has advantages of a small size and a simple structure, which makes it ideal for interconnection with different wearable devices operating within 2.4 GHz wireless system range.

A wide locking range injection locked frequency divider (ILFD) with a low power consumption for 60GHz applications is presented. The locking range of the ILFD is enhanced by reducing the parasitic capacitances of the transistors. The cross-coupled transistor and injected transistors are integrated to become a compact structure, which exhibits simple routing and induces less parasitic capacitances. To verify the proposed structure, the ILFD was fabricated using 65 nm CMOS technology. It has a measured locking range of 55.3 GHz to 67 GHz (19%) with 0 dBm input power. The circuit dissipates 1.98 mW at 0.5 V supply voltage without the output buffers.

We report the second-harmonic generation (SHG) from single GaN nanowire. The diameter of the GaN nanowire varies from 150 to 400 nm. We present a model for the SHG process in the GaN nanowire; the analysis shows quantitatively that the SHG is dominated by its surface area. The effective second order nonlinear optical susceptibility (χ⁽²⁾_eff) increases as the diameter of the GaN nanowire decreases. For 150-nm diameter GaN nanowire, χ⁽²⁾_eff reaches 136 pm/V.

In this paper, a wideband metasurface reflector that converts polarization of plane wave to the cross polarization with a double-square-shaped unit cell is presented, and the principle of polarization conversion based on polarization synthesis is also presented. The proposed structure has a unit cell with the longest dimension of 0.37 wavelength, a width of 0.23 wavelength, and a thickness of about 0.09 wavelength. 95% or more of the incident wave power is converted to cross-polarization covering a fractional bandwidth of 32.4% at 8.5 GHz.

A double-layer frequency selective surface (FSS) with dual rings is used as a reflector in the design of an Archimedean spiral antenna (ASA) with low radar cross section (RCS) and uni-directional characteristics. The proposed FSS presents a stopband in the range of 2 GHz to 4.7 GHz, which is applied to ASA to form a unidirectional radiation pattern with front to back ratio (FBR) values larger than 10 dB in the stopband, and the maximum FBR value is up to 25.26 dB. Compared with the reference antenna with the same-size metallic ground, the proposed FSS reduces the RCS about 2.5-38 dB in the frequency ranges of 4.8-30 GHz. And the FSS antenna also exhibits better axial ratio characteristics in the frequency range of 2.8-8.1 GHz. The composite structure is compact, with a total height of 0.18 wavelength at the lowest analysis frequency of 2 GHz. Measured results indicate that the proposed antenna reproduces the inherent wideband of the original ASA from 1.6 GHz to 8.1 GHz. Meanwhile, the gain of the ASA is increased by 3 dBi. Full-wave simulations and measurements prove that the novel FSS reflector can be employed to replace a metallic ground which realises a uni-directional ASA with broadband low RCS, high gain and good circular polarization (CP) performance.

A new miniaturized and ultra-thin non-resonant element-class of convoluted frequency selective surface (FSS) structure with reduced overall thickness is presented and empirically verified. The proposed FSS structure, which could be capable of providing a first order narrow band pass response for X band applications, is made up of three metallic layers separated from one another by two dielectric substrates. The outer layers are made up of convoluted inductive grids， and the inner layer is a non-resonant structure composed of convoluted square slot array. A first-order band pass response FSS with a centre frequency of 10.5 GHz and fast roll-off characteristics is presented. The overall element thickness of the proposed FSS is λ/56, which is smaller than previously proposed miniaturized structures. The comparison between all patch layers with the proposed structure which is not an all patch layers is explicated in detail with its convoluting effects. The validity of this design procedure is verified with an equivalent circuit model, and a sample is fabricated and measurement done using a WR 90 waveguide setting for experimental verification.

In this paper, a new super-resolution and highly stable DOA estimation technique of coherent sources is introduced. Furthermore, the proposed technique is applied to the data collected from the AWR1243 mm-wave 76-81 GHz frequency modulated continuous wave (FMCW) radar to estimate the DOAs of real targets. A virtual antenna array is proposed to increase the array aperture size and the dimension of the data covariance matrix which effectively helps in de-correlating the received signals and in increasing the number of detectable sources and hence improving the detection resolution. Moreover, a significant improvement in the DOA estimation capability is achieved by handling the frequency domain of the received signals instead of their time-domain representations. That is because the signal to noise ratio (SNR) is increased by a multiplication factor when it is transformed using FFT which acts as a filter for the noise. The simulation results proved the superiority of the proposed technique compared to the state of the arts in this field, especially at low SNR that approaches -35 dB.