In this paper, we present a broadband flexible RFID sensor tag antenna to detect the concentration of aqueous solutions. The proposed RFID tag antenna sensor with a T matching network is based on a printed dipole whose arms are loaded with circular disk patches. The structure is printed on a Kapton polyimide flexible substrate. The sensing mechanism of the RFID tag antenna is based on the change of sensitivity of the RFID tag antenna that occurs with the variation of aqueous solution concentration. The proposed sensor is designed using CST Microwave studio, and its various parameters are optimized in order to have a broadband impedance matching that covers the entire RFID band (860-960 MHz). The experimental setup is small, rapid, contactless, and inexpensive. Results are presented for NaCl and sugar aqueous solutions with concentrations ranging from 0% to 80%.

A novel technique for designing a dual-band reconfigurable aperture coupled cylindrical dielectric resonator antenna is introduced here. The design is based on loading an aperture coupled cylindrical dielectric resonator antenna with a varactor diode located along the lines of the feed network. Loading the antenna with the varactor shifts the first and second resonant frequencies of the antenna. The resonant frequency can be continuously shifted from 4.75 GHz to 4.96 GHz in the lower band, and the resonant frequency of the higher band is shifted from 6.31 GHz to 6.40 GHz as the varactor diode bias voltage is increased from 1 V to 5 V. The proposed antenna offers a stable broadside radiation pattern at both bands and across the entire tunable frequency range for different bias voltages. The parametric analysis on the slot position is done to control the first and second resonant frequencies of the dual-band antenna. The proposed antenna plays a vital role in C-band (4 GHz-8 GHz) applications.

Through-wall imaging (TWI) is one of the useful applications nowadays in microwave tomography field. Reconstructing image of an object becomes more challenging when it is obscured by walls. In practice, the inclusions of noise worsen the reconstruction results. In this paper, Forward-Backward Time-Stepping (FBTS) in time inversion technique is utilized and integrated with Wall Direct Subtraction (WDS) method to reconstruct unknown object behind walls. The investigation includes two types of walls that are homogeneous and heterogeneous. The object is surrounded by closed walls. With noise added in the setup, Singular Value Decomposition (SVD) and Savitzky-Golay (SG) filtering method are used to eliminate the noise and enhance the reconstructed image of an object. The results show that WDS integrated with FBTS has successfully mitigating wall clutter from both homogeneous and heterogeneous walls, and also improves image reconstruction of a hidden object. Further, by using the proposed noise reduction method, lower MSE values can be achieved.

This paper presents design analysis of a compact CPW fed Wearable Textile Antenna with Dual Band notched characteristics for UWB applications. The proposed wearable textile antenna is designed on two different dielectric substrates; leather and denim with copper foil as conducting element. The performances of the designed textile antenna are compared on two substrates. Band-notched filtering characteristics are achieved by inserting semicircular split ring resonators on the conducting element. The first notch band is obtained from 2.3 GHz-2.5 GHz for Bluetooth application band, and the second notch band is obtained from 3.3 GHz-3.6 GHz for WiMAX application band. The simulated and measured frequency results show that the antenna has an impedance bandwidth of 1.8-10 GHz and reflection coefficient less than -10 dB, except at the two eliminating bands. The proposed antenna is designed and simulated using Ansys HFSS Electromagnetic Simulator. The prototype of the antenna has been developed on the denim substrate, and its performance is measured and compared with the simulated ones.

The paper presents a new coplanar waveguide (CPW)-fed ultra-wideband (UWB) dual circularly polarized (CP) slot antenna. For realizing UWB, a wide slot is introduced in the ground plane of the proposed antenna. The circular polarizationis achieved by introducing a semi-circular stub in the square ground plane. The antenna contains two symmetrical CPW-fed ports at left and right edges to generate dual circular polarization. The evolution steps of the proposed CP antenna are presented, and antenna parameters are optimized to obtainthe desired level of isolation, return loss, and axial ratio bandwidth (ARBW). The measured impedance bandwidth (S₁₁ ≤ -10 dB) of the antenna is 13.5 GHz (2.5-16 GHz); 3-dB ARBW is 75.23% (2.67-5.89 GHz); and isolation greater than 17 dB is obtained in the CP band. The designed dual feed CP antenna has low profile, light weight, compact size, and could be suitable for polarization diversity applications for reducing the effect of multipath fading.

This paper presents a novel Circularly Polarized (CP) microstrip array antenna with circular shape and slotted by an elliptical ring for X-band communication. This array antenna consists of 4 paths. Each patch is designed with a unique model, and the purposed antenna is mainly circular-shaped. An elliptical ring slot is set at the center of the circular-shaped patch. And a pair of triangle shapes employed as truncation factor is placed at the edge of the circular-shaped antenna. This microstrip array antenna is developed by 2 × 2 patches in a sequential rotation mode with relative phases 0˚, 90˚, 180˚ and 270˚. Total dimension of this array antenna is 60.92 mm × 60.92 mm. The simulated result shows a good agreement with minimum requirement. The center frequency of the antenna design is 8.2 GHz with low-frequency at 8 GHz and high frequency at 8.4 GHz. The proposed antenna produced under -10 dB S₁₁ of 21.9%, maximum gain of 12.47 dBic at the center frequency, and axial ratio bandwidth obtained 12.2%. Simulated result has been validated by fabrication and measurement, then the structure of the antenna design is fabricated on NPC-H22A with a thickness of 1.6 mm and dielectric constant of 2.17. Complete investigation and experimentation are presented in the next sections.

Last decade has witnessed dramatic advancements in wireless charging distance of magnetic resonant coupling wireless power transfer (MRCWPT) for various portable electronic devices. Driven by the demand of cost-effective and compact system working for multiple receivers, a novel omnidirectional MRCWPT system with a single wire wound spiral transmitter and a single power source is proposed in this work. Besides, an equivalent circuit model is established to derive the power transfer efficiency (PTE) of this novel MRCWPT system. Finite element simulation results have shown that the magnetic field distribution for the proposed model is uniform in all directions. And the PTE of the system depending on the distance between the transmitter and receivers is demonstrated to be independent of the receiving angles. Finally, the theoretical analysis of the simulation results is verified by practical experimental results, which shows that the PTE of the system reaches 60% at the distance of 160 mm and the resonant frequency of 15.5 MHz.

Moving target ship imaging in large sea area has always been the focus of military and civilian attention. Due to the limitation of pulse repetition frequency (PRF), there is a contradiction between wide mapping band and azimuth accuracy. The nonlinearity of PRF can also cause discontinuity of mapping band. Therefore, this paper proposes a method of digital beamforming-scan on receiving (DBF-SCORE) beam scanning based on airborne phased array radar to achieve the requirement of scene mapping band with lower PRF. The adaptive Capon spectrum estimation is used to dynamically adjust the beam pointing so that it can always point to the moving target for accurate imaging. Considering the nonuniform sampling of the transmitting pulse period of the antenna, the azimuth nonuniform Fourier transform (NUDFT) algorithm is used to re-sample the nonuniform periodic signal of the multi-channel receiving antenna and obtain the uniform spectrum signal. Finally, fine focusing of moving target is achieved by local phase gradient algorithm (PGA) algorithm, and accurate imaging of moving target in large sea area is realized. The validity of the algorithm can be verified by simulation and real data imaging, which can be used for reference in phased array SAR imaging of moving targets.

Due to the restrictions of low-resolution radar system and the influence of background clutter during the target detection, it is difficult to classify different kinds of low-resolution radar aircraft targets. In this paper, we propose a multifractal correlation method in the optimal fractional Fourier domain found by fractional Fourier transform (FrFT), in which we extract the multifractal correlation features of aircraft target echoes and do target identification combined with the support vector machine. The experimental results show that FrFT can enhance the multifractal correlation characteristics of aircraft target echoes; the multifractal correlation features extracted from the optimal fractional Fourier domain can effectively distinguish different types of aircraft; and the classification and recognition rates of the multifractal correlation method in the optimal fractional Fourier domain are higher than that of the multifractal correlation method in time domain and the multifractal method in the optimal fractional Fourier domain.

A rigorous analysis of hexagonal slot with electromagnetically coupled parasitic element is presented in this article. The wide band feature of the antenna highly depends on the shape and location of the parasitic element and tuning stub. It is found that tuning and overlapping of resonating modes at lower frequency band are mainly achieved by parasitic element. The proposed antenna exhibits the bandwidth of 120.83% from 1.45 to 5.8 GHz for S₁₁<-10 dB. The parameters of the antenna and circuit model are studied. The role of individual resonators in circuit modeling is also explained. Series of equations for lower cutoff frequency and other resonating frequencies are deduced after inspecting the surface current distribution. At frequencies 2.27, 4.17, and 5.2 GHz, the simulated and measured far fields are compared.

This article describes multiresonance behaviour to achieve ultra-wideband (UWB) characteristics of a co-planar waveguide (CPW) fed circular patch antenna with a ground plane reflector by using fractal elements and rectangular defective ground structure (RDGS) technique. The patch consists of a circular disc with six ring type fractal elements on the periphery of the disc and slotted defective ground surface (DGS) at the bottom of an FR4_epoxy dielectric substrate to increase the antenna bandwidth. The antenna resonates at frequencies of 5.4 GHz, 9 GHz, & 10.8 GHz with return loss better than -20 dB. The proposed antenna also exhibits UWB characteristics with (≤ -10 dB) impedance bandwidth of 170.4% in the frequency range from 1.8 GHz to 11 GHz. This covers the whole UWB range from 3.1 GHz to10.6 GHz as defined by FCC. The antenna exhibits nearly omnidirectional radiation pattern and a gain ranging from 1 dBi to 6.8 dBi within the operating frequency range (1.8 GHz-11 GHz). An equivalent circuit model of the proposed antenna is developed, and the circuit response is obtained. All the measured results are found in good agreements with the simulated ones. The proposed antenna is suitable for applications in Wi-Fi, IEEE 802.11a Wireless LAN, WiMAX, ISM bands, wireless communications, etc.

The presence of the O and X modes in the HF skywave propagation has previously been investigated experimentally for their role in providing polarization diversity and improving channel capacity when a MIMO structure is employed. A mathematical treatment of MIMO channel modelling and capacity improvement has also been reported but limited to NVIS links only. This paper reports the mathematical derivation of the HF 2×2 polarized MIMO channels when cross-dipoles, i.e., a pair of orthogonally polarized horizontally-oriented dipoles, are used at both ends to examine the cross-polarization property and the capacity improvement factor (CIF), with the transmitter-receiver range being near enough to allow single-hop paths only but also distant enough to make the trajectory oblique. Results on the cross-polarization property suggest that the power contributions of the waves from the two transmitters that arrive at each receiver are equal. In addition, the signal from any one of the transmitters is received by the two receivers with unbalanced powers that depend on the phase shift difference between the O and X paths. It is also observed that on average the MIMO channels with oblique paths have lower capacity than the NVIS MIMO channels due to the reduced orthogonality between polarizations of antennas in the dual-antenna system at each end. The above hypotheses are confirmed through ray-tracing simulation and field measurement over a 575 km HF radio link.

Space Sensing Models promulgates the channeling sequels of interstellar environs. A fractal array with sun-shaped irregular molds has arisen to solar activities by interchangeably pointing in the direction of sun and off source with beam swapping, whilst weighing the sun's position (psi, phi)-space (phi demarcates the antenna azimuth proportionate to north, psi contours the beam elevation over horizon) and its solid radioactivity hoarded in the antenna's beam width. The research feedback has incidents of solar fluxes and brightness temperatures to depict sun's activity. Phenomenally, nature-space fractals have been crucial quintessence in intuiting sun's after math pertaining to weather and biological sways {Weierstrass C(x,y)} on landscape, swirling with fractal clock underpinning magnetic flipping and irradiance fluctuations at phase vicissitudes have periodically wedged on territory. The remote alliance algorithms with random fractal contours have subsidized paths of self-affine topographic surfaces and space-earth stoichiometry. In this paper, antenna solar scan corollaries at X-band to detect the solar activity on fractal boresight physiognomies of 3-dB HPBW around 0.5° solar diameter with 36° crest atmospheric stray radiations (SLL) rope inpetite sidelobes 60˚ near the core flamboyant region, return loss S₁₁<-10 dB at X/Ku-band on horizontal and vertical tilting bearings have been estimated.

This article discusses about the design and development of an ultrathin triple band microwave absorber using a miniaturized metamaterial structure for near-unity absorption characteristics. In order to design a miniaturized metamaterial (MTM) absorber unit cell with triple band response, two resonators, named as Structure-I and Structure-II, are configured within the single unit cell. The geometrical proportions of the suggested resonators have been chosen in such a manner so that Structure-I can contribute one absorption band while Structure-II can contribute two absorption bands. Therefore, the combination of two resonators offers triple band response with the highest absorption values of 99.04%, 99.62%, and 99.33% at the frequencies of 4.25 GHz, 8.35 GHz, and 11.06 GHz, respectively. Additionally, the suggested absorber unit cell claims miniaturization with total electrical size of 0.156λ₀ × 0.156λ₀ × 0.014λ₀, where λ₀ corresponds to the free-space wavelength at the first peak absorption frequency of 4.25 GHz. Additionally, the electric field and vectored surface current distribution along with the input impedance graph has been used to discuss the absorption methodology of the suggested structure. Further, the MTM belongings of the suggested structure have been illustrated with the dispersion curve.

In this paper we determine the statistical distributions of the co- and cross-polarized Layered Rough Surface Index (LRSI) for three-dimensional layered structures with an arbitrary number of slightly rough interfaces illuminated by an electromagnetic plane wave. For infinite surface areas and Gaussian centered height distributions, we show within the framework of the first-order small perturbation method that the LRSI under a given observation direction is a random variable, whose statistical distribution is only function of two parameters. Contrary to the intensity ratio which follows a heavy-tailed distribution, the LRSI has finite mean and variance. For a structure air/clayey soil/rock, we analyze the influence of a snow layer upon the probability laws in the cases of Gaussian or exponential correlation functions.

This paper presents a new technique to enhance impedance bandwidth of single layer half width microstrip leaky wave antenna (HW-MLWA) with continuous main beam scanning. The enhancement is realized by etching four circular slots on the radiation element. Two of the circular slots are placed close to the feed port, and the others are close to the matching load. The wide main beam scanning is between +12˚ and +70˚ when operation frequency sweeps between 4.3 GHz and 6.5 GHz. A comparison between the Uniform HW-MLWA (reference) and the proposed HW-MLWA with circular slots is providedto study the effectiveness of the added circular slots. The proposed HW-MLWA is fabricated and tested. The measured impedance bandwidth is 49.9% (4.28 GHz to 7.13 GHz) with peak gain 10.31 dBi at 5 GHz, hence the proposed antenna can be considered as a suitable candidate for C-band applications.

This paper proposes an improvement to the whale optimization algorithm (WOA), which is based on the Levy flight technique. The improvement allows improved whale optimization algorithm (IWOA) to have a good diversity of population, faster convergence and overcome premature. The test by using different benchmark functions is conducted to demonstrate the effectiveness of improvement on the algorithm performance. Finally, IWO algorithm is applied to optimize the problems of two-way pattern of MIMO radar system, involving the achievements of sidelobe reduction, deep null and wide null at the prescribed directions. The obtained numerical results demonstrate that IWOA can not only efficiently fulfill the expected deep nulls and wide nulls at the prescribed directions, but also enable the peak sidelobe level to retain in the smaller level at the same time than several state-of-the-art algorithms.

Simple, compact and high sensitivity metamaterial-inspired microfluid sensors are developed to detect and classify dielectric fluids in the X-band regime using reflection coefficients. Multi-negative refractive index band metamaterial structure is specifically designed as a sensing enhancer, where the multi negative bands can effectively trigger the electromagnetic properties, as well as enhance the differentiation between the testing samples. The geometry of the metamaterial enhancer and its arrangement with the microfluidic channel and radiating patch antenna are optimized to reach the highest sensitivity of the samples' depiction. The proposed sensors were tested on methanol and ethanol traces, where sets of complex permittivity were varied. Distinguishable frequency responses generated from different samples at three resonances specify the capability of classifying the fluid concentration.

A new design idea of MIMO beamforming antenna array for compact and thin handheld devices is investigated, where the beamforming function is used for transmitting and the MIMO function for receiving. The new design idea is illustrated by an antenna array consisting of eight printed planar inverted-F elements operating at GSM1900 (1880-1920 MHz) and LTE2300 (2300-2400 MHz). The 8-element antenna array is printed on an FR4 substrate of dimensions 136 mm × 68.8 mm × 1 mm. By using the radiation pattern diversity, good isolations, envelope correlation coefficients and mean effective gains are achieved for MIMO receiving. To realize the beamforming function when the antenna is used for transmitting, an optimal feeding mechanism is introduced by the method of maximum power transmission efficiency, which is then implemented by a continuously adjustable feeding circuit board. With the optimized feeding mechanism, the gain of the antenna array in the desired direction can be significantly enhanced. The effects of the human body on the performance of antenna array are also examined, and the results indicate that the proposed design still exhibits good MIMO and beamforming performances in a practical scenario.

This paper reports the influence of antennas on radio signal propagation in tunnels and underground mines. Radio signal propagation measurement results in a concrete tunnel and underground mines using antenna types with various radiation patterns, i.e., omnidirectional, Yagi, patch, and circular, are reported. Extensive measurements were taken in various scenarios which include vertical, horizontal, and circular polarization for line-of-sight (LoS) radio signal propagation at four frequencies (455, 915, 2450, and 5800 MHz) that are common to many voice and data transport radio systems used in underground mines. The results show that antenna pattern has a strong influence on the uniformity of radio signal propagation gain in the near zone and typically does not significantly influence behavior in the far zone, except for a constant gain offset.