Vol. 90

A wireless charging system for electric vehicles has two parts which are located inside and outside the vehicle respectively, and energy is transmitted from the outside part to inside part through a loosely coupled transformer. The energy transmission efficiency is directly related to the power conversion efficiency of the entire wireless charging system. This paper aims to improve the transmission efficiency of the DC transformer of the wireless charging system through studying compensation design method of DC transformer. A dual-tap rectifier is applied at the secondary side of the transformer, and a capacitor is connected in series on the primary side. Two capacitors are connected in series on the secondary side. By quantitative analysis on DC transformer efficiency, the relationship among efficiency, switching frequency and compensation parameter is obtained. The compensated DC transformer realizes soft switch and further improves transformer efficiency. Finally, simulation and experiment on the wireless charging system with magnetic induction are conducted to verify the improved transformer design. The simulated and experimental results show that the average compensated DC transformer efficiency has been improved by 1.248%. Thus the designed DC transformer can effectively improve the energy transmission efficiency, and reduce voltage stress of the power device.

Defected ground structures (DGSs) are often utilized in planar filters and antennas for compactness and spurious frequency suppressions by creating defects or slots on the ground planes. One disadvantage of conventional DGS filters is that the overall dimension increases as the order of the filter increases. In this research, we proposed an asymmetric finger-shape DGS which created multiple equivalent LC resonators when combining with a capacitive microstrip gap on the top. In contrast to the conventional high-order DGS filter by generating many DGSs on the ground plane, the finger-shape DGS provided a high-order bandpass response with one single DGS due to the capacitances between the top metallic strip and the ground plane. Therefore, we developed a wide-band, high-order, and spurious frequency suppressed microstrip bandpass filter with a compact size. To achieve these features, different filter design techniques were exploited including stepped impedance resonator (SIR), series-coupled resonator, and nger-shape DGSs. The main advantage of our DGS filter was that it had a higher-order and wider bandpass responses than other harmonic-suppressed work. A prototype was designed, fabricated, and measured with a calibrated vector network analyzer (VNA) where the simulations matched with the measurements. The finger-shape DGS filter demonstrated a passband centered at 2.35 GHz with a fractional bandwidth of 72.3%, the spurious frequency suppression up to 8.5f₀ where f₀ was the center frequency of the passband, and a compact size of 0.034λ₀² where λ₀ was the wavelength corresponding to f₀.

This work describes the path loss of radio propagation for wireless sensor network in the outdoor fruit orchard which is one of the common agriculture environments. The measurement was conducted in the jackfruit orchard in the 2.45 GHz band. Unlike other studies conducted in the fruit orchard environments, the variation of path loss over the relative angles between the plant rows and the line-of-sight direction from the transmitter to the receiver is identified. The equivalent vegetation obstruction model is proposed as the function of the equivalent number of trees along the line-of-sight to better represent the angular path loss variation. This leads to the proposal of the path loss prediction approach at any point in the fruit orchard by using a few measurement efforts. This work also introduces the Monte Carlo simulation using the numerical electromagnetic scattering computation called hybrid T-matrix method to evaluate the relative angular vegetation loss of a single tree that is used as the input to determine the equivalent number of trees. The evaluation results suggest that it can further reduce the measurement workload required for the proposed path loss prediction approach.

In this paper, a circularly polarized slot-patch antenna for nanosatellite is presented. The novel design of the circularly polarized wave conducted by two asymmetrical rectangular-truncation techniques implemented on a circularly-slotted-patch on the front side and a deformed-shifted-feedline on the back side of the substrate. The antenna is printed on substrates with the dielectric constant of 2.17 and thickness of 1.6 mm. The resonant frequency of the proposed antenna is set at 2.2 GHz with the minimum requirement of the axial ratio bandwidth (ARBW) of 300 MHz. The proposed antenna produces under -10 dB impedance bandwidth (IBW) 1.2765 GHz or equal to 58% (1.7235-3 GHz) with Left-Handed Circular Polarization (LHCP). The average antenna gain reaches 4.5 dBic at 2.2 GHz and the ARBW 327.5 MHz or about 14.88% (2.0275-2.355 GHz). This paper includes the description and presentation of the completed discussion.

Due to the existence of power coupling the virtual synchronous motor (VSG) will lead to overshoot fluctuations in the power adjustment process, thus affecting the control performance. Compared to the traditional direct current control inverter based on coordinate transformation, VSG model is more complex and difficult to achieve decoupling. This paper presents a dynamic power decoupling method by studying the coupling relationship between active power and reactive power of VSG. Firstly, the inverter grid-connected model is established, and the power expression is analyzed when the inverter output impedance is negligible. Then the virtual active power and reactive power expressions are obtained through coordinate transformation. Several key state equations and virtual states of the VSG are obtained. The power expression performs small signal perturbation to obtain the dynamic model of the VSG. From this, the dynamic model of the VSG can be analyzed to obtain the coupling relationship between the dynamic powers, and the series power compensation is used to decouple the dynamic power coupling. Finally, the correctness of the theoretical analysis and the effectiveness of the decoupling method are verified by simulation and experiments.

This work proposes an approach to retrieve the ferrite's electromagnetic properties in a single compact configuration, simpler than the traditional measurement systems. The ferrite under test is fully inserted into a rectangular waveguide with a magnetic bias. The complex scattering parameters are theoretically analyzed under the consideration of modal effect at isotropy-anisotropy interfaces. Extraordinarily sharp Fano resonances are observed in the scattering spectra, originating from the multimode interference inside the magnetized ferrite. There is good agreement among theoretical, experimental, and full-wave simulation results. This model can be further utilized to simultaneously retrieve all ferrite properties, including permittivity (ε), saturation magnetization (4πM_s), and magnetic linewidth (ΔH) from the measured scattering parameters, facilitating the designs and applications of ferrite devices.

A Direction Finding (DF) algorithm for small aperture DF systems is proposed. Traditionally, small aperture DF systems lack of beamforming capabilities and therefore require manual rotation, which may affect the Angle of Arrival (AOA) estimation accuracy. Based on Characteristic Mode (CM) Analysis, a Multi-Feed Structural Antenna (MFSA) is developed that utilizes an electrically small platform as a radiator. This paper chooses a Small Unmanned Aerial Vehicle (SUAV) as a design platform. The overlap of all Individual Element Radiation Patterns (IERPs) of the proposed MFSA covers the entire azimuth plane. In this way, beamforming and null steering of the MFSA on the azimuth plane can be achievedby linearly combining all weighted IERPs. A new method based on Vector Singular Value Decomposition (SVD) is proposed to determine the weight vector of beamforming (``Sum'' pattern) and null steering (``Difference'' pattern) in a specific direction. Based on the ``Sum-Difference'' delta method, the AOA of the Radio Frequency (RF) signal source can be estimated. A small aperture VHF DF system with a multi-channel digital-IF receiver is developed to experimentally verify the proposed concept. The evaluation results show that the AOA estimation RMS error is 1.55°, and the false detection rate is significantly improved.

In this work, we propose a balun embedded driver stage to enhance the bandwidth and minimize the chip size of a differential CMOS power amplifier. By removing the passive input transformer, the bandwidth and chip size are improved. The proposed driver stage acts as an input balun as well as the driver stage for the power stage. The proposed driver is composed of a cascade connected PMOS, an inductor, and NMOS to generate the differential output signal. For the function of the input balun, the gate of the PMOS is connected to the drain of the NMOS. To verify the feasibility of the proposed balun embedded driver stage, we design a differential CMOS power amplifier for 5-GHz IEEE 802.11n WLAN applications. The designed power amplifier is fabricated using the 180-nm SOI RF CMOS process. The measured 3-dB bandwidth is approximately 2.5 GHz. The chip size of the fully integrated power amplifier, including input and output matching networks and test pads, is 0.885 mm². The measured maximum output power is 20.18 dBm with a PAE of 10.16%.

This work presents a novel structure of semi-circular floral shape slotted antenna for an ultra-wideband (UWB) including WCDMA, Bluetooth and Wi-Max applications. Initially, a semi-circular floral shape radiator is designed by inserting an elliptical slot in patch with partial rectangular ground plane. Further, three rectangle symmetrical stepped slots are inserted in ground below 50 ohm micro-strip (MS) feed line which is integrated with stepped quarter wave transformer to achieve an ultra-wide impedance bandwidth. The proposed antenna structure achieves UWB of 4-18 GHz which cover 127% (S₁₁<-10 dB) fractional bandwidth (FBW). Furthermore, ground plane is modified by loading three asymmetrical capacitive folded strip resonators (CFSR), which provide an additional lower frequency communication bands 2100 MHz (2-2.2 GHz), 2400 MHz (2.34-2.47 GHz), and 2700 MHz (2.69-2.75 GHz) for applications of WCDMA, Bluetooth, and Wi-Max, respectively. An optimized dimension of the proposed antenna is 30×30 mm² (1.1λ₀ ×1.1λ₀), which is designed and fabricated on an FR-4 substrate having thickness 1.6 mm and dielectric constant 4.3. The proposed design is computed by Electromagnetic (EM), ADS simulator, and simulation results are validated with measured results.

The Cramer-Rao lower bound (CRLB) for calculating errors and accuracy of direction-of-arrival (DOA) estimation is discussed for a number of planar waves arriving on an antenna array. It is well known that the geometry of antenna arrays imposes restrictions on the performances of the direction-of-arrival estimation. In particular, the influence of the directivity factor of the individual antenna elements on the accuracy of the DOA estimation of the radio emission sources for circular (cylindrical), cubic and spherical antenna arrays consisting of the directional antenna elements is investigated. The directivity factor of antenna elements is changed within wide limits in order to determine the values at which the high accuracy of the direction-finding can be achieved. It is shown that further increasing the directivity factor of each antenna element makes the mean square error in the determination of the coordinates of the signals increase as well. The exact expression for the Cramer-Rao lower bound for the DOA-estimation variance calculation depending on the antenna directivity and the geometry is presented. The obtained exact equation shows the most important factors that the direction-of-arrival estimation accuracy is dependent on. A technique of obtaining antenna arrays with optimal directional elements locations is proposed. Those arrays allow increasing DOA estimation accuracy by several times.

This paper presents a reconfigurable, wide-beam antenna with a modular main radiator for base station applications. The addition of new spectrum and the path to 5G create unique antenna requirements in terms of patterns and impedance matching capabilities. The antenna in this paper exhibits a wide azimuth beamwidth up to approximately 180^o, and implements a modular approach where the antenna can be recongured for impedance matching requirements. Two congurations of the wide-beam antenna are presented; the rst conguration covers the 1.7-2.7 GHz band for 3G/4G/LTE applications where multiple wireless carriers would use the same antenna as a neutral site. This antenna provides wide-beam operation and a 10-dB return loss from approximately 1.64-2.76 GHz. The measured return loss over the 1.7-2.7 GHz band is better than 13 dB. A second conguration of the antenna is tuned for performance from 1.9-2.4 GHz where measured return loss better than 19 dB is achieved in this band. Simulated and measured return losses and patterns are presented that show very good agreement between simulation and measurement, and thorough parametric pattern analysis is presented for the baseline antenna configuration.

A general synthesis approach is proposed for reflectarrays using second order Phoenix cells. It relies on an original spherical representation that transforms the optimization domain in a continuous and unbounded space with reduced dimension. This makes the synthesis problem simpler and automatically guarantees smooth variations in the optimized layout. The proposed mapping is combined with an Artificial Neural Network (ANN) based behavioral model of the cell and integrated in a min/max optimization process. Bi-cubic spline expansions are used to decrease the number of variables. As an application, a contoured beam for space communication in the [3.6-4.2] GHz band is considered. The gain improvement compared to an initial Phase Only synthesis (POS) is up to 1.62 dB at the upper frequency. Full wave simulation of the final array is provided as a validation.

In this communication, a novel design of a hybrid open slot antenna is investigated and experimentally verified. The proposed structure comprises a slotted tuning stub, a proximity fed parasitic element, and slotted ground plane. Tuning and overlapping of best matching frequencies f_r1, f_r2, f_r3, f_r4, f_r5, f_r6, and f_r7 are accomplished by varying the dimension of the parasitic element and elliptical slot which is the part of the elliptical slot. The experimental results reveal that this antenna covers the fractional bandwidth (BW(%) = 200 * (f_h - f_l)/(f_h + f_l)) of 139.5% from 0.98 GHz to 5.5 GHz for |S₁₁|<-10 dB which is suitable for GSM 1800, WiMAX, PCS, and ITM-2000. After the analysis of current distribution, mathematical equations are developed for frequencies 1.04, 1.52, 3.06, 3.67, and 4.58 GHz. The structural analysis is also carried out for optimization and to know the electromagnetic behaviour of the antenna. Asymmetric radiation patterns are found at resonating frequencies due to open slot geometry.

The generalized function approach for modeling radio wave scattering has been used to develop expressions for the scatter from rough surfaces and for horizontally-stratified media. The scattered field from rough surfaces can be found in closed form if plane wave incidence is assumed, but the method is valid for any realizable source without resorting to using Hertz vectors. This approach was originally developed to model high frequency surface wave radar scattering from the ocean or across layers of ice covering the ocean using vertical polarization. This paper presents three extensions to the existing theory: the x component of the scattered field for rough surface scattering is developed, the assumption of a good conducting surface assumption is removed for a rough surface and the scatter from stratified media is simplified in terms of a scattering coefficient. The shape of the scattered field is not affected by the relative permittivity, but the intensity of the scattered field is weaker due to an increased transmission of energy through the surface. The goal for this research is to better understand how signatures from ice-penetrating radar can be used to distinguish hazardous ice ridges from other ice features. Here, ice ridges are modeled as layered media with a rough surface.

A wideband high gain circularly polarized layered cylindrical dielectric resonator antenna (DRA) that operates in a higher order mode is proposed in the X-band frequency range. The antenna consists of two dielectric layers having different dielectric constants and radii. The results demonstrate a considerably improved performance as a result of adding the outer dielectric layer, where wider impedance and axial ratio bandwidths have been attained in conjunction with a higher broadside gain of ~14 dBic. A prototype has been built and measured with close agreement between experimental and simulated results.

In this paper, the main problem to be solved is how to achieve magnetic resonance imaging (MRI) accurately and quickly. Previous work has shown that compressive sensing (CS) technology can reconstruct a magnetic resonance (MR) image from only a small number of samples, which significantly reduces MR scanning time. Based on this, an algorithm to improve the accuracy of MRI, called regularized weighting Composite Gaussian smoothed l₀-norm minimization (RWCGSL0), is proposed in this paper. Different from previous methods, our algorithm has three influential contributions: (1) a new smoothed Composite Gaussian function (CGF) is proposed to be closer to the l₀-norm; (2) a new weighting function is proposed; (3) a new l₀ regularized objective function framework is constructed. Furthermore, the optimal solution of this objective function is obtained by penalty decomposition (PD)method. It is experimentally shown that the proposed algorithm outperforms other state-of-the-art CS algorithms in the reconstruction of MR images.

In this paper, awideband dual-polarized multi-dipole antennawith a compact radiator size is developedfor 2G/3G/LTE base station applications. The original antenna is composed of a pair of crossed square loop dipoles (SLDs) and two big Y-shaped feeding lines. Thanks to the adopted capacitive coupling, a wide impedance bandwidth is obtained with dual resonant modesin the low and middle frequency bands. Owing to the circular chamfersin thecrossed SLDs, the dual resonant modes are away from each other. Thus, a compact radiator size is implemented, and it is about 0.382λ₀×0.382λ₀ (λ₀ is the wavelength at center frequency of operation). To further widen the operating bandwidth of the antenna, a pair of crossed rectangular loop dipoles (RLDs) and four small Y-shaped feeding lines are introduced to generate a new resonant mode at high frequency. As a result, the impedance bandwidth of the proposed antenna is enhanced.Based on the optimized dimensions of the simulated antenna model, a prototype is developed, fabricated and tested. Measured results show that the proposed antenna has a relative impedance bandwidth of 53.9% from 1.68 to 2.92 GHz at two ports for VSWR<1.5. Within the operating impedance bandwidth, the measured port-to-port isolation is better than 30 dB. In addition, a stable gain of 8.2±0.5 dBi and a stable radiation pattern with 66°±4° half-power beamwidth (HPBW) in the horizontal plane are achieved across the whole bandwidth of operationfor dual polarizations. Finally, the proposed antenna is suitable for base station applications.

A dual-passband frequency selective surface (FSS) is designed in this paper. Two passbands are 2-3.4 GHz and 5.5-6.8 GHz, respectively. It is used as a spatial filter to improve the radiation and scattering performance of an antenna. The structure is combined with two layers. One is metal, and the other is intermediate medium. The requirements of wide-band, polarization-independent, wide incidence angle and miniaturized FSS with a thickness of only 0.0085λ are achieved by parameter optimization. When the FSS is used to improve the proposed microstrip antenna, the relative bandwidth can be increased by 31.4% and 50%, and the peak gain is increased by 2.53 dB and 1.86 dB at 5.8 GHz and 6.4 GHz, respectively. Meanwhile, the maximum RCS reduction of the microstrip antenna is 16 dB. On the other hand, the FSS is able to be applied to a dipole antenna to improve the transmission coefficient and phase. Simulation and measurement results of the transmission coefficient and phase of the antenna are almost the same.

In this paper, a new compact microstrip low-pass filter (LPF) with ultra-wide stopband characteristics is presented. The combinations of DGS-DMS along with quasi octagonal resonators are employed in the design of the proposed filter to achieve compact size and ultra-wide stopband suppression level. The proposed filter has been designed, simulated, optimized and tested. The design procedure is validated using the commercial full-wave EM MoM simulator Microwave Office. Simulated as well as measured results of low-pass filter exhibit sharp roll-off (ξ) of 19 dB/GHz and creating transmission zero at around 7.8 GHz with attenuation level -54 dB. The measurement results show good agreement with the simulations. The cutoff frequency of the proposed low-pass filter is 2.4 GHz with the insertion loss less than 0.3 dB. The ultra wide stop band with over 20 dB attenuation extended from 3.42 GHz to 12 GHz. The spurious passband suppression up to six harmonics (5fc) is achieved for the proposed design. The addition of two parasitics DGS elements in the ground plane leads to suppression of the undesired harmonics and thus to improve the stopband. The size of the whole structure is less as (0.44λ_gx0.26λ_g) with λ_g = 68 mm. The proposed filter is useful for microwave L band, GPS system, and RADAR applications.

Proof-of-concept is presented of a novel slot antenna structure with two excitation ports. Although this antenna provides a wide impedance bandwidth, its peak gain and optimum radiation efficiency are observed at its mid-band operational frequency. The antenna structure is etched on the top side of a dielectric substrate with a ground plane. The antenna essentially consists of a rectangular patch with two dielectric slots in which multiple coupled patch arms embedded with H-shaped slits are loaded. The two dielectric slots are isolated from each other with a large H-shaped slit. The radiation characteristics of the proposed antenna in terms of impedance bandwidth, gain and efficiency can be significantly improved by simply increasing the number of radiation arms and modifying their dimensions. The antenna's performance was verified by building and testing three prototype antennas. The final optimized antenna exhibits a fractional bandwidth of 171% (0.5-6.4 GHz) with a peak gain and maximum radiation efficiency of 5.3 dBi and 75% at 4.4 GHz, respectively. The antenna has physical dimensions of 27×37×1.6 mm³ corresponding to electrical size of 0.0452λ₀×0.0627λ₀×0.0026λ₀, where λ₀ is free-space wavelength at 0.5 GHz. The antenna is compatible for integration in handsets and other broadband wireless systems that operate over L-, S-, and C-bands.