In this paper, a low-cost polycarbonate substrate is used for the design of antennas operating in the 28 GHz band. First, a corner bent inset fed patch antenna is proposed with a forward gain of 7 dBi and a front to back ratio of more than 18 dB indicating minimal radiation towards the user post-integration with a mobile terminal. In order to cater to the landscape mode, a corner bent tapered slot antenna is also proposed with a gain of 7 dBi. An overlapped architecture is investigated to demonstrate orthogonal pattern diversity with an effective radiating volume of 0.12λ₀³, a port to port distance of 0.13λ at 28 GHz, and mutual coupling of less than 27 dB without deterioration in the pattern integrity of the corresponding modes. Detailed simulated and measured results are presented with justification.

In high-speed strip-mode Synthetic Aperture Radar (SAR), the motion between the radar and moving targets during the pulse duration must be considered; however, the existing SAR raw data simulator is unable to handle the case of the moving targets for high-speed SAR exactly. As for the issue, an accurate Point Target Reference Spectrum (PTRS) of the moving targets for high-speed SAR is first derived in the paper, which considers the motion. Further, an accurate and efficient extended scene generator for high-speed SAR included static and moving targets is proposed according to the spectrum. Finally, point targets and extended scene are performed to validate the proposed approach, and its computational complexity is analyzed.

Cellular technology is moving towards its 5th generation (5G) that will employ millimeter wave (mmWave) frequencies in the attempt to offer more spectrum and multi-Gigabit-per-second (Gbps) data rates to mobile devices.Various unfavorable propagation phenomena affect mmWave communications, rain attenuation being the most severe one. Various rain attenuation prediction models can be taken into account in the design of terrestrial links based either on cumbersome statistical regression, when sufficient local experimental data are available, or on analytical models where only local rain rate measurements are provided. In this paper, a new prediction method for the rain attenuation is proposed based on a bivariate model for the numerical estimation of the effective path length of a millimeter wave terrestrial link and on Weibull distribution forthe representation of the point rainfall rate statistics. To validate the proposed prediction method, the actual data taken into account are extracted from experiments included in the databank of ITU-R SG3.The numerical results obtained show a significant improvement of the prediction accuracy compared to existing prediction models.

Field modulation magnetic gear is a transmission device with broad development prospects. It has the advantages of no friction, no pollution, low maintenance, and easy installation. Magnetic gear models with different gear ratios are established. The input and output torque waveforms of different models are compared. The influences of the number of pole pairs of the inner rotor (P₁) and the number of pole pairs of the outer rotor (P₂) on torque ripple are analyzed. According to the principle of magnetic field modulation, the torque ripple of magnetic gear is greatly affected by P₁ and P₂. Research results show that the torque ripple can be effectively reduced by selecting the magnetic gear with P₁ = 4, P₁/P₂ = 1/(n+0.25) or 1/(n+0.75) (n is a natural number).

The precise positioning of an autonomous robot in the wireless sensor network with a high refresh rate is important for well-ordered and efficient systems. An orthogonally transmitted simultaneous multi-beam system improves the geometric dilution of precision (GDOP) and expedites the refresh rate of the system. In this paper, the beam-pattern analysis of an electronically steerable multi-beam impulse radio ultra-wideband (IR-UWB) transmitter tag is presented and demonstrated. The multi-beam transmitter tag is optimized to improve the real-time positioning accuracy of an autonomous robot for an indoor positioning and tracking system. Two linear arrays of four elements with an inter-element spacing of 18 cm and 10.2 cm are proposed and optimized. The array with spacing 10.2 cm is intentionally configured to produce orthogonal beams, which eventually provides better geometric dilution of precision. The beam steering-angle analysis is performed to better utilize the steering delay range and scanning angle range. The radiation intensity in the direction of the transmitted beam is calculated. Consequently, an intensity table for the Gaussian-modulated multi-cycle IR-UWB beamforming array is proposed. The intensity table gives an easier way to calculate the peak intensity and the number of cycles of the radiated IR-UWB pulse in the transmitted beam direction. The proposed beamforming transmitter arrays are observed to achieve the scanning range from -60˚ (-90˚) to +60˚ (+90˚) with a scanning resolution of 5˚ and 8˚ in the measurements.

A compact ultra-wideband (UWB) antenna with tunable band notched characteristics is proposed. Varactor loaded, two via edge located (TVEL) and fractal electromagnetic band gap (EBG) structures are designed for tunable band-notched characteristics. The varactor diode near the TVEL EBG tunes the band notch frequency for WiMAX (2.8-4.0 GHz) band, while another varactor near fractal EBG structure tunes band-notch frequency for WLAN (4.7-6.2 GHz) band. The varactors are independently controlled to achieve WiMAX and WLAN notched band. Notch frequencies can be continuously tuned by varying the bias voltage across the varactors. The proposed antenna of 24×24 mm² dimensions is fabricated on an FR4 substrate. A good agreement between simulation and measurement results is obtained. A continuous band notch tuning from 2.8 to 4.0 GHz and 4.7 to 6.2 GHz is obtained using varactor diodes having capacitance in a range of 0.497-2.35 pF.

There are millions of people in the world exposed to weather-related land deformation hazards. These weather-related mass movement activities are most likely due to climate change, the decrease of permafrost area, the change in precipitation pattern, etc. Landslide is the most common land deformation incidents reported in Malaysia for the past few years. Therefore, Remote Sensing and Surveillance Technologies (CRSST), Multimedia University (MMU), Malaysia has developed the ground-based synthetic aperture radar (GBSAR) as a tool to monitor the high-risk area, which is prone to landslide continuously. Preliminary testing of the GBSAR has been conducted in Cameron Highland, Malaysia to verify the performance of the GBSAR and its capability of detecting landslide. However, the phase stability of the GBSAR is one of the most crucial factors that affect the detection capability of GBSAR, especially when it comes to the sub-mm measurement. This paper reports the phase stability study of the GBSAR and presents an empirical model for interferometric phase statistics.

When an implantable medical device is in radio energy transmission, due to eddy current effect, the temperature of the device will rise, causing a safety risk. In order to study the distribution law of its temperature field, this paper adopts the analysis method of electromagnetic-thermal-fluid-solid multi-physics coupling, and establishes a two-dimensional transient equivalent model of an implantable medical device radio energy transmission system, adopting the analysis method of the electromagnetic-thermal-fluid-solid multi-field full coupling. Among these, electromagnetic heat is applied as the heat source, considering the influence of factors, such as heat conduction and convection. By means of simulated calculation, this paper acquired one-dimensional, two-dimensional and three-dimensional images, whose temperature and efficiency changed with frequency Moreover, their distribution laws are also obtained. In order to verify the correctness of the simulation, this paper conducts infrared temperature measurement experiments to prove the rationality of the analysis through comparing the simulation results. The research findings of this paper can provide a basis for the design of radio energy transmission system for the implantable medical device, improve the safety of implantable medical devices, and reduce the occurrence of medical accidents. Meanwhile, it has certain reference value to the clinical application of implantable medical devices.

The present paper studies the characteristics of electromagnetic scattering from vegetation models constructed as random wire structures for the purpose of PolSAR imaging and ground surface cover recognition and classification. Radar vegetation index (RVI) has been developed for the purpose of vegetation growth monitoring. Anew method is proposed to use the RVI as an accurate monitor for the natural grassland height taking into account the operational parameters such as the PolSAR look angle and the operating frequency. Also, the present paper addresses a problem that may lead to false indications of the RVI measured for grassland areas. It frequently occurs that some of the narrow long leaves of the grass cloud are quasi-parallel and of nearly equal lengths leading to the generation of internally resonant modes. The enhancement or diminishing of the backscattered field at such internal resonances may give false indication of the RVI and, hence, wrong information can be estimated such as the water content and the grass height. A new method is proposed to model the natural grasslands as clouds of electrically conductive random curly strips for the purpose of obtaining the backscatter coefficients and, hence, the corresponding RVI. The error in height estimation using the proposed method due to the existence of the internal resonances is numerically investigated.

A novel and effective architecture of tunable multiband balanced bandstop filter (MBBSF) is introduced for the first time in this paper. Each symmetrical bisection of the proposed branch line structure consists of K series cascaded tunable N-band sections to realize a reconfigurable K-th order N-band response in differential mode (DM) operation. The main advantage lies on the fact that all these N bands can be tuned simultaneously or each band independently. Moreover, it maintains a high common mode rejection ratio (CMRR) for all the tuning states by incorporating open stubs in the symmetrical plane of the balanced structure. To validate the proposed topology, a balanced dualband tunable BSF is designed where the two DM stopbands tune in the range of 1.16 GHz-1.29 GHz and 1.6 GHz-1.76 GHz, respectively. The lower and the upper bands maintain a constant absolute bandwidth (ABW) of 115 MHz and 135 MHz, respectively, and stopband rejection is better than 20 dB for each band. The fabricated prototype occupies an area of 0.31λ_g², and the experimental results show a good agreement with the simulation results.

This paper presents the design of a 3.8 ~ 8.0 GHz wide-band quadrature coupler on a multi-layer package substrate. The asymmetric coupled-line 3-dB quadrature coupler has been designed on a four-layer microwave substrate, with a 10-mil thick top layer of Roger's RO4350B substrate press-joined to a 20-mil thick bottom layer of RO4350B, through 4-mil thick bond-ply material RO4450B. In the proposed design, the second and third metal layers are used as coupling layers, while the fourth (bottom) layer provides four signal pads and one large ground pad for connection with the test circuit. The mutual coupling is achieved through the overlay of coupled lines. Four VIA holes are used for signal transition from coupling layers to the bottom-layer pads. The SMD package quadrature coupler provides the ease of integration with other microwave circuits. The quadrature coupler chip size is 4.0 mm x 8.0 mm x 0.9 mm. The measurement results show a close resemblance to the EM-simulation results. The measured results depict reasonably flat 3-dB coupling and quadrature phase difference. The amplitude imbalance remains within 1.0 dB, while the phase imbalance always remains much less than 3.0 degrees. The return loss and isolation are better than 13 dB, throughout the whole frequency band. The proposed design is quick and simple. The manufacturing process is also cost-effective. To the best of the author's knowledge, these measured performance parameters in 71% fractional bandwidth associated with the compact size of the self-packaged device are better than those of the earlier published 4-layer design schemes of wideband quadrature couplers.

An analytical approach for calculation of the dyadic Green's functions inside the rectangular cavity over a broad range of frequency is presented. Both vector potential and electric field dyadic Green's functions are considered. The method is based on the extraction of the Green's function at an imaginary wave number from itself to obtain a rapidly convergent eigenfunction expansion of the dyadic Green's function. The extracted term encompasses the singularity of the Green's function and are computed using spatial expansions. Results are illustrated for rectangular cavity up to 5 wavelengths in size with thousand of cavity modes obtained by the 6th order convergent expansion. It is shown that for an accurate and broadband simulation, the proposed method is many times faster than the Ewald method.

In this paper, we consider a MIMO wiretap system in wireless sensor networks (WSNs), where the confidential signal sent to the legitimate receive (Bob) may be eavesdropped by the eavesdropper (Eve). Assuming that only partial channel state information (CSI) can be obtained by the transmitter, we consider both worst case (WC) and outage-constrained (OC) robust secrecy optimizations. To solve the WC design, we propose to linearize these logarithmic determinant terms. After linearization, we tackle the CSI uncertainty using the Nemirovski lemma. Then, an alternating optimization (AO) algorithm is proposed to solve the reformulated problem. On the other hand, to solve the OC design, we transform the probabilistic constraint into safe and tractable reformulation by the Bernstein-type inequality (BTI) and large deviation inequality (LDI), and an AO algorithm is proposed. Numerical results are provided to demonstrate the performance of the proposed scheme.

This paper presents a multi-band annular ring antenna that is obtained from a single-layer probe-fed substrate integrated waveguide based on a graphene material, with three top plan slits. In order to create a multi-bands antenna, we conduct simulation of the antenna structure based on CST/HFSS, so we use parametric tuning to adjust TM modes. Simulations show a good results between the two methods (finite element method and integral method) CST and HFSS Simulators. The bandwidths for three modes are 340 GHz in first mode, 346 GHz in the second mode, and 104 GHz in the third mode. The simulation gains at TM₁₁, TM₀₂, and TM₁₂ are 8.2 dB, 8 dB, and 11 dB, respectively. The proposed antenna can be used in therahertz applications.

Accurate measurement of atmospheric particulate matter (PM) absorption coefficient is highly required for study of earth climate change and for monitoring of air quality. In addition, multi-wavelength measurements of PM absorption can provide information on the PM chemical composition (black carbon or brown carbon). A multi-wavelengths photoacoustic (MW-PA) spectrophone operating at 444, 532 and 660 nm was developed and deployed for filter-free characterization of wavelength-dependent optical properties of PM mass absorption coefficient (MAC) and absorption Ångström coefficient (AAC). It is worth noting that to date no any AAC of volcanic ashes determined by filter-free measurement have been reported. The developed MW-PA spectrophone was deployed to an intensive field campaign measurement of environmental PM in Grenoble (France). Side-by-side inter-comparison measurements of ambient PM showed a good correlation between the developed MW-PA spectrophone and a reference instrument aethalometer (Magee scientific, AE33).

This paper demonstrates a three-port coaxial fed antenna system for wireless local area network (WLAN) access points, consisting of two dipoles and a patch, radiating at 5.2 GHz with impedance bandwidth of 150 MHz. The antennas are designed for pattern diversity in the end-fire and broadside orientation with an individual gain of 4.5 dBi, which is further enhanced to 6 dBi after integrating with unit-cell structures. The gain enhancement for individual antennas is achieved by strategically integrating transmission type and reflective type sub-wavelength structures for patch and dipoles respectively. The realized ground plane is shared among the three antennas. The measured results show that the return loss of the antennas is unaffected by the unit-cell loading and has an isolation of less than 26 dB throughout the band and across the ports for a port-to-port distance of 0.25λ.

This paper provides a sound wireless power transfer (WPT) recharging solution for on-road automated guided vehicle (AGV) system. In this solution, multiple transmitting coils serve as power transmitters (TXs), and a receiving coil in AGV serves as a power receiver (RX). The multiple TXs are along a straight track for dynamic charging to AGV. The circuit model of multiple-TX and single-RX WPT system is first constructed based on circuit theory (CT), and then current-optimized scheme based on Lagrangian multiplier method is proposed to tune the currents in multiple TXs to maximize the power delivered to the load (PDL). The equal current (EC Case) flowing through each TX is compared with the optimal current (OC Case). Through contrastive analysis, the OC Case shows its advantages in PDL. Finally, the theoretical analysis results are confirmed by the results of full-wave electromagnetic simulation.

In recent years, through-wall imaging (TWI) has gained much research interest because of urgent needs of civilian, security, and defense applications. TWI based on compressive sensing (CS) method can produce high resolution, assuming that the wall parameters are known in prior. However, it is difficult to know the exact wall parameters in actual scenarios. With unknown wall parameters, the dictionary matrix is not a fixed one. Therefore, CS theory cannot be directly applied in the TWI. This paper presents a parametric sparse recovery method for TWI with unknown wall parameters. The original reconstruction problem is reformulated into a joint optimization one which can be solved with an alternating minimization algorithm. Specifically, the proposed method performs the wall parameter estimation and sparse image reconstruction in an iterative procedure. With the estimated wall parameter which is or close to the true one, the high fidelity and high-resolution image is obtained. Experimental simulations show that the proposed method can obtain an autofocus image and improve the image quality.

Because of the current commutation and the double salient pole structure of bearingless switched reluctance motors (BSRMs), the torque and suspension force have large ripples when traditional current control methods are used. According to the special structure of the double stator BSRM (DSBSRM), the direct decoupling of torque and suspension force is realized. Therefore, the DSBSRM can be controlled separately as a conventional 12/8 SRM and a four-poles active magnetic bearing. In order to achieve the suppression of the torque ripple and improve the robustness of speed, a direct torque control (DTC) strategy using second order sliding mode (SOSM) speed controller is proposed. In order to achieve the suppression of the suspension force ripple and rotor displacement chattering, a direct suspension force control (DSFC) strategy is proposed as well. Then the SOSM-DT/DSFC model is established by simulink. The results of simulation show that the torque ripple, suspension force ripple and rotor radial displacements of DSBSRM can be reduced respectively. Moreover, the proposed control strategy has better robustness and dynamic performance than traditional control strategy.

In the wireless power transfer system (WPT) via magnetically coupled resonance, the lateral misalignment between the transmission coil and the receiving coil may affect the mutual inductance, then the transfer efficiency may be decreased, and the output power may be fluctuated, which lead to an unstable system. In this paper, a calculation method of the mutual inductance of an asymmetrical two-coil structure is presented. Based on the mutual inductance calculation method, an optimization method of quasi-constant mutual inductance is proposed. The key parameters of each coil can be obtained by using the proposed method. The mutual inductance can be kept constant when the misalignment is changed. And the output voltage and efficiency are also nearly constant with different misalignments. Finally, the setup of the asymmetric two-coil WPT system via magnetically coupled resonance is designed. Calculation, simulation, and experimental results validating the proposed method are given.