Vol. 95

In recent years, FMCW CSAR (frequency modulation continue wave circular synthetic aperture radar) is more and more widely used in military reconnaissance and sea surface target recognition. However, due to the influence of external factors, it cannot move in an ideal uniform circular trajectory, resulting in low imaging resolution. In this paper, the problem of motion errors caused by nonuniform circular motion is analyzed, and the phenomenon of range unit broadening and sidelobe increase caused by nonuniform circular motion errors is simulated. The echo model is characterized by error parameters. Based on the compressed sensing imaging algorithm, motion error parameters are estimated by parametric sparse representation. The least squares method and gradient descent method are applied to estimate motion error parameters. Simulations are conducted to show that both of the methods can reach the goal that the motion compensation is realized. The result of simulations and measurement data demonstrate that the algorithm can correct nonuniform circular motion errors better and further improve the imaging resolution.

In this article, a solution of the plane wave diffraction problem by two axisymmetric strips with different dimensions is considered. Fractional boundary conditions are required on the surface of eachstrip. Several cases of strip's dimension, configurations, and fractional orders are considered, and numerical results are obtained. The near electric field distribution, Total Radar Cross Section frequency characteristics, and the Poynting vector distribution in the vicinity of these strips are calculated and illustrated. For the fractional order 0.5, the solution is found analytically.

As seen from this article, a novel hepta-band metal-rimmed antenna is proposed. The volume of the proposed antenna is small, and no lumped elements are used. The proposed metal-rimmed antenna is competitive for modern mobile application. The illustrated antenna could be divided into several parts: main ground plane, metal rim, two L-shaped ground slots sharing one open end, an L-shaped branch extended from right edge of main ground, a microstrip feedline located at the top surface of the substrate, a meandered branch located at the back side of the substrate, and a 2mm slot located at the middle of the metal rim's top edge. For lower band, GSM850 and GSM 900 are provided by two bezel loop modes generated through capacitive coupling of feedline. For upper band, DCS, PCS, UMTS, LTE2300, and LTE2500 are covered by multiple modes of two L-shaped slots, a meandered strip and feedline. With the proposed structure, the volume of the proposed antenna could be further reduced. All the mentioned operating bands are achieved in a small area of 620 mm² on a 115x70 mm² system board. Note that the proposed antenna has achieved such a small volume on a relatively small system board without any lumped elements. The rest of this paper will describe the antenna configuration, the analysis of working principle, parametric analysis, and the experimental results are also given and discussed.

The self-interference problem of linear frequency modulated continuous wave (LFMCW) radar is a known issue that limits the radar's detection range. Analog adaptive interference cancellation (AIC) technique is effective to mitigate the self-interference problem. However, we find that the phase difference between the error signal and reference signal paths may significantly deteriorate the stability of the AIC system. Therefore, in this paper, we analyze the effect of phase difference on system stability through the mathematical modeling and simulation. We find that the system is stable when the phase difference is between -90 and 90 degrees, and diverges when it is between 90 and 270 degrees. Therefore, to avoid system instability, we propose to add a phase shifter in the reference signal path to compensate the phase difference. The experiment results show that compared with the traditional delay-based compensation method, our phase compensation based method can increase interference cancellation ratio (ICR) by 15 dB for a single-antenna system and 12 dB for a dual-antenna system.

Direction of arrival estimation (DOA) is critical in antenna design for emphasizing the desired signal and minimizing interference. The scarcity of radio spectrum has fuelled the migration of communication networks to higher frequencies. This has resulted in radio propagation challenges due to the adverse environmental elements otherwise unexperienced at lower frequencies. In rainfall-impacted environments, DOA estimation is greatly affected by signal attenuation and scattering at the higher frequencies. Therefore, new DOA algorithms cognisant of these factors need to be developed and the performance of the existing algorithms quantified. This work investigates the performance of the Conventional Minimum Variance Distortion-less Look (MVDL), Subspace DOA Estimation Methods of Multiple Signal Classification (MUSIC) and the developed estimation algorithm on a weather impacted wireless channel, Advanced-MUSIC (A-MUSIC). The results show performance degradation in a rainfall impacted communication network with the developed algorithm showing better performance degradation.

An improved mixed phased/retrodirective array is presented. The phase conjugation technique will be achieved in base band instead of in intermediate frequency (IF) band. Canceling the need to the intermediate frequency stage in the receiver will reduce the complexity and cost of the system. The ability to the entire processing of the tracking array function to be applied using software defined radio (SDR) system is added. The effect of the phase errors at each channel is compensated phased array, and the noise performance of the tracking array is improved. Also an expanded analytical study of the noise performance of the array to include the impact of the phase errors on the array performance is presented. The proposed equivalent one-channel model of the N-channel array provides a clear and efficient way to characterize the noise performance of array receiver systems with any amplitude tapering and also considering the phase errors. The improvement provided by the mixed phased/retrodirective array compared to the traditional phased array is evaluated. The of array size on the tracking array performance in the presence of phase error is discussed. A monopulse tracking array is taken as an example.

In this paper a staircase fractal curve is applied on a microstrip line fed truncated corner square patch antenna to achieve Super Wide Band (SWB) operation. The proposed antenna exhibits an impedance bandwidth from 0.1 GHz to 30 GHz with a ratio impedance bandwidth of 300:1 for S₁₁ ≤ -10 dB. The bandwidth enhancement of the proposed antenna structure due to the fractal curve is shown in a step by step manner. The Bandwidth Dimension Ratio (BDR) of the proposed antenna design is obtained as 496675. Relatively stable omnidirectional radiation pattern and satisfactory value of gain are obtained over the operation band. Time domain analysis has also been performed to check the applicability of the proposed design as SWB antenna.

The problem of the shielding evaluation of an infinitesimally thin perfectly conducting circular disk against a vertical magnetic dipole is here addressed. The problem is reduced to a set of dual integral equations and solved in an exact form through the application of the Galerkin method in the Hankel transform domain. It is shown that a second-kind Fredholm infinite matrix-operator equation can be obtained by selecting a complete set of orthogonal eigenfunctions of the static part of the integral operator as expansion basis. A static solution is finally extracted in a closed form which is shown to be accurate up to remarkably high frequencies.

This study explores the variability in the electric field, plasma number density, and plasma velocity driven by high-frequency (HF) radio wave injected into the vertically stratified ionosphere at a millisecond time scale after switch-on of the radio transmitter. It was found that the modeconversion process of electromagnetic (EM) waves took place at the reflection heights of both the R-X (right-circularly polarized extraordinary wave, R-X) and L-O (left-circularly polarized ordinary wave, L-O) modes. The ionospheric electron number density was remarkably oscillatory. A depletion of ionospheric ion number density at the L-O mode turning point and two ion number density peaks on each side of the O-mode reflection region were discovered. The turbulent layer of the ion density peak at the bottom of the critical height shifted downwards, which qualitatively conforms to the observations made at the Areciboand the EISCAT. The vertical electron velocity oscillated near the L-O mode reflection point. The vertical ion velocity remained positive above the reflection height of the L-O mode and remained negative below this height. These results, which were derived using realistic length scales, ion masses, pump waves, and other plasma parameters, are consistent with theoretical predictions and prior experimental observations, and should thus be useful for understanding the linear and nonlinear interactions between the HF EM wave and the ionospheric plasma at the initial stage.

An electrically small Asymmetric Co-planar Strip (ACS)-fed MIMO antenna for USB wireless applications is proposed. MIMO antenna consists of two electrically small antennas inserted inside a 3D-printed USB prototype. Electrically small ACS-fed antenna consists of an F-shaped monopole radiator with a U-shaped slot inserted into it. The proposed antenna is compact with dimensions 11 × 20 × 0.508 mm³. The proposed MIMO antenna has dual bands which caters to WiMAX-3.5/5.5 GHz, WLAN-5.8 GHz, and C-band-6.3 GHz. The proposed architecture attains reasonable gain for the available aperture. Also, ACS-fed antenna achieves fractional bandwidth of 22% and 20% in the lower and upper bands respectively complying with the theoretical bandwidth as defined by Chu's limit. Isolation between the radiators is greater than 15 dB in both the operating bands. Radiation patterns have high integrity, and actual USB deployment is presented. Simulation and measurement results are presented.

The purpose of this work is to miniaturize a rectangular patch antenna which resonates at 2.4 GHz. To achieve this, we present a new geometry of a pi-shaped slot with three annular rings as a Defected Ground Structure (DGS). DGS is a periodic etched structure or a periodic sequence of configurations, and it has been used to switch the resonance frequency from starting value 13 GHz to an ending value at 2.4 GHz without any changes in the areas of the actual rectangular microstrip patch antenna (RMPA). The proposed antenna is structured on an FR-4 substrate with thickness 1.6 mm and permittivity 4.4. The general size of the ground plane is 34 × 34 mm². Using the optimal position and dimension of the pi-shaped slot on the ground, the resonant frequency is reduced to 2.4 GHz, which signifies an 81.53% decrease. Proposed antennas with and without DGS are simulated by using High-Frequency Structure Simulator (HFSS) and Advanced Digital System (ADS) Agilent technology, fabricated, and measured for Wireless Local Area Network (WLAN) application.

This paper proposes a wearable antenna for Wireless Body Area Network (WBAN) that operates at the 2.45 GHz medical band. The antenna is enabled by coplanar waveguide, and the impedance bandwidth of the antenna is expanded by combining a circular slot with asymmetric slots. In order to reduce the radiation of the antenna back lobe and improve the antenna gain, a new 2×2 Artificial Magnetic Conductor (AMC) is designed and loaded under the monopole antenna. The radiation of antenna back lobe is effectively reduced due to the addition of AMC reflector. Also, the front-to-back ratio of the demonstrated antenna is higher than 20 dB, achieving a forward gain of 7.47 dBi and Specific Absorption Rate (SAR) lower than 0.15 W/kg, in the ISM band.For further research, the antenna is fabricated and tested, showing a strong agreement between simulation and measurement. Meanwhile, the antenna has stable performance under the bending condition, meeting the practical application requirements of wearable equipment.

In this paper, the outage probability performance of energy harvesting based partial relay selection aided non-orthogonal multiple access (NOMA) system under outdated channel state information is studied. The source to relays link is assumed to follow Rayleigh fading distribution while the relay nodes to users are subjected to Nakagami-m distribution. The relay nodes employ an energy harvesting power splitting-based relaying protocol to transmit the source information to the users.At the destination, each user is equipped with multiple antennas, and maximum ratio combining is considered for signal reception. In order to evaluate the system performance, the outage probability closed-form expression for the concerned system is derived. The results demonstrate the significant impact of system and channel parameters on the system performance. In addition, the advantage of NOMA over the conventional orthogonal multiple access is also presented. Finally, the accuracy of the derived outage expression is validated through the Monte-Carlo simulation.

The goal of this study is to analyze the effect of tri-band antennas in 2.45, 3.6, 3.8, 4.56 and 6 GHz frequencies, which cover Wi-Fi and some of the future 5G frequencies for wearable smart glasses applications. The latter 4 frequencies are studied for the first time for smart glasses. In order to provide a thorough analysis, first a simulation study for the head model with the proposed antennas is performed, then a realistic experiment by using a semi-liquid gel phantom head model with the infrared thermography method is conducted, and also 4 male subjects are included to analyze temperature rise effects on the skin. The phantom prepared for this study is also validated for its robustness and matching parameters. The SAR values and temperature rise due to the usage of smart glasses calculated by simulation modeling, bio-heat analytical solution, and infrared thermography technique are in good agreement. The temperature rise of the skin regions gets monotonically increased in the duration of usage. The simulations for all indicated frequencies are performed. Also, to provide comparable and practical results, the phantom study is compared with simulations for 2.45 GHz. According to the quantitative data obtained on the liquid-gel head phantom and on the subjects, the temperature increase is below 1ºC, and its compliance with safety standards is determined. The results show that tri-band antennas for these frequencies can be safely used; however, a limiting behavior for the power is necessary for lower frequencies due to the increasing SAR values and temperature rise.

To study the transient magnetic field and temperature field of a dry-type transformer core and analyze the core loss and hot spot temperature rise of the core, a magnetic and temperature field coupling analysis method based on finite element method was proposed: the transient magnetic field of dry-type transformer was calculated first, and the core loss under a no-load condition was obtained. Then, the core loss density distribution was coupled to the temperature field as the heat source, and the temperature field distribution in the transformer was calculated by the fluid-thermal coupling method to obtain the hot spot temperature and the position of the core. Compared with the traditional average heat source method, the temperature field distribution calculated by the proposed method is close to the actual temperature distribution of the core. Finally, based on this method, the magnetic field and temperature field of the transformer core under different excitations were calculated, and the effect of harmonics on the core loss and temperature rise of the core was analyzed.

In this paper, microwave breast cancer detection is investigated using the Ultra-Wide Band (UWB) radar imaging technique. A novel calibration approach based on the Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT) is used and adapted to work in this field. Using this method, many high amplitude undesired responses can be removed like early time clutter, late time clutter, and the mutual coupling between antennas. Using an electromagnetic simulation tool, a numerical phantom with a heterogeneous structure and dispersive dielectric properties is made for simulating the interactions of the electromagnetic fields with various breast tissues and investigating the proposed approach. The calibrated signals show the capability of the proposed algorithm in separating the tumor/glandular responses from the clutter. Also, the results of the proposed algorithm are compared with the Wiener algorithm results which are considered one of the best techniques to remove clutter, reduce late time clutters in the multistatic, and enhance the beamformer algorithm performance. Moreover, we propose the use of Transmitting-Receiving Antenna Separation Distance (TRASD) to limit the reflection angles from the voxel under the calculations of DAS and IDAS beamforming algorithms.

In this paper a novel design of microstrip fed L-shaped arm slot and notch loaded RMPA (Rectangular Microstrip Patch Antenna) with mended ground plane for wide bandwidth is presented. The proposed prototype antenna is fabricated on an FR-4 (Fire retardant) substrate with dimension 30×30.8 mm² and 1.6 mm thickness. The proposed design is analyzed and simulated using high frequency structure simulator (HFSS) tool version 15. The analysed results are validated through fabrication and measurement results. The analyzed result shows 96.1% maximum radiation efficiency at 2.9 GHz whereas overall efficiency is more than 85% over the entire frequency range and experiment achieves gain 8.4 dB at 7 GHz. The designed antenna achieves 119.39% impedance bandwidth with more than 5 dB gain over the operating frequency range of 2.41 GHz to 9.55 GHz. For better performance and analysis of proposed antenna, a parametric study has been carried out to analyze the effects of variations in the following --- slot and notch dimensions loaded on the patch as well as variations in ground length. The designed antenna can be utilized for various applications incorporating Bluetooth, WLAN, Wi-Max, and UWB operation.

This paper evaluates the performance of different configurations of MIMO antenna operating in the 5G band with the effect of user's hand in data mode and suggests an optimized configuration to mitigate hand effects. A dual-band four-element MIMO antenna is used. All antenna elements (AEs) are identical planar inverted-F antenna (PIFAs) with a lower frequency band (LB) from 3.3 to 3.8 GHz and an upper frequency band (UB) from 5.2 to 6 GHz. In addition, four different configurations to place the AEs on the chassis are selected including worst and optimized configurations as well two intermediate cases. Results show that similar values of ECC are produced for both cases without and with user hand. These values are less than 0.20 on most frequency range, except the worst case configuration which has some high ECC values close to unity. Unlike ECC, TE is severely affected by user's hand as well as by the different configuration. TE of each AE under hand effect is degraded differently according to the thickness of hand tissue that covers it. TE in the optimized configuration without user's hand ranges between 50 and 95% in both frequency bands. However, this range deteriorates when user's hand effect is considered, between 40% and 15% in LB, and from 35% to 41% in the UB. Multiplexing efficiency analysis reveals that MIMO performance is mainly determined by TE, and the impact of the low ECC is insignificant. This indicates that improving the performance depends on improving the TE of AEs and optimizing their positions on the chassis to reduce interaction with user's hand. Moreover, the loss in ergodic capacity due to user's hand compared with free space is increased from 5 to 40% in the LB, and it is more stable in the UB and ranging between 12 and 17%.

This paper proposes low profile, high gain and wideband circularly polarized (CP) microstrip antennas (MSA), using gap coupled parasitic patches (PPs) on superstrate layer. Printed and suspended probe fed, CP MSAs are designed on a 1.59 mm thick FR4 substrate, and an array of closely spaced hexagonal PPs are printed on the bottom side of the 1.59 mm thick FR4 superstrate and placed at a height about λ₀/8, above the ground plane, where λ₀ is the free space wavelength, corresponding to the central frequency of the operating frequency band. The gap coupled hexagonal PPs are not only used to enhance the axial ratio bandwidth (AR BW) and gain of the antenna, but also used to reduce impedance and gain variation of the antenna over the operating frequency band. `Ant9' is a suspended MSA with 7 hexagonal PPs. A prototype `Ant9' is fabricated and tested, which provides a peak gain of 9 dBi, S₁₁ < -10 dB, gain variation < 1 dB, and AR < 3 dB over 4.9 to 6.45 GHz frequency band. ARBW of 27.3% is achieved. The proposed `Ant9' covers three frequency bands viz., 5.15 to 5.35 GHz, WLAN band, 5.725 to 5.875 GHz, ISM band, and 5.9 to 6.4 GHz, Satellite C band. The space fed antenna configuration reduces the cross polar radiation level (CPL) and increases the efficiency of the antenna. A prototype antenna is fabricated and tested. The measured results agree with the simulation ones. The overall size of `Ant9' is 0.96λ₀×0.96λ₀×0.136λ₀.

Modeling how electromagnetic waves scatter from a distribution of rough plates poses many applications. Certain systems may be easy to approximate with planar geometry, but use of numerical field solvers to determine the radiated fields could take a long time for nontrivial structures. We propose a new approach based on the Kirchhoff approximation. This method will consider the case of multiple rough, finite-sized rectangular plates. The solution was used for developing software to determine the scattering of waves off of a distribution of rough plates of arbitrary position and orientation between a transmitter and receiver. The method considers each plate individually, calculating the coherent and incoherent scattered fields. Provided that all plates and the transmitter and receiver are sufficiently spaced, we calculate the total fields by summing the result from each individual plate. For many practical situations, the distance from the plate to the receiver may not be much greater than the size of the plate. We will show that the common far-field approximation of the Green's function is not valid for these cases, and we will have to use a more accurate approximation of Green's function.