A broadband circularly polarized antenna array is proposed in this paper. The array consists of four sequentially rotated feed groove-backed strip antennas. Compact size (46 mm × 46 mm × 1.6 mm), wide impedance bandwidth (4.62-9.92 GHz), and wide 3 dB axial ratio bandwidth (4.48-8.52 GHz) can be observed. The measured peak gain is 7.5 dBi at 8.2 GHz, and good agreement between the simulated and measured results can be achieved.

Performance of optical add-drop multiplexer (OADM) for 400 channels with data rate of 20 Gbps for super dense wavelength division (SD-WDM) multiplexing system has been investigated in terms of varying transmission distance from 50 km to 250 km and 80 km to 240 km for enhancing optical communication. Long haul amplification is maintained by RAMAN-EDFA hybrid optical amplifier (HOA). Evaluation is carried out in terms of bit error rate (BER) and dispersion.

A novel four-step weakly conditionally stable hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) algorithm in three-dimensional (3-D) domains is presented in this paper, which is suitable for a finer discretization in one dimension. Based on the exponential evolution operator (EEO), the Maxwell's equations in a matrix form can be split into four sub-procedures. Accordingly, the time step is divided into four sub-steps. In addition, by taking second-order central finite-difference approximation for both the temporal and spatial derivatives, the formulation of the proposed four-step HIE-FDTD method is obtained. The proposed four-step HIE-FDTD algorithm is implemented, in which the implicit scheme was applied only in one direction with a fine grid, and the explicit scheme was applied in two other directions with coarser grids. Compared with the existing HIE-FDTD methods, the proposed method has a weaker Courant-Friedrichs-Lewy (CFL) stability condition (and), which means that the proposed method can improve computational efficiency by taking larger time step size. Since the CFLN stability condition of the proposed method is determined by the smaller grid size of the two coarse grid sizes, the proposed method is suitable for analyzing the electromagnetic objects with fine structures in one direction effectively. Besides, the numerical dispersion analysis is given, and the (Δt ≤ 2Δx/c and Δt ≤ 2Δz/c) comparisons of the numerical dispersion analysis among the proposed method, traditional FDTD method, ADI-FDTD method, and two existing HIE-FDTD methods are given. Finally, to testify the computational accuracy and efficiency, numerical experiments of the five FDTD methods are presented.

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.

A triple two-level nested array (TTNA) configuration is proposed for direction-of-arrival (DOA) estimation of multiple time-space signals. The proposed TTNA consists of multiple two-level nested arrays, and the distance between two adjacent nested arrays is also given according to a nested array. As traditional nested arrays, it can generate a hole-free different co-array. Compared with some preexisting nested arrays, the proposed nested array can offer more degrees of freedom (DOFs). The closed-form expression of DOFs and the array configuration are given. Moreover, the detailed process for the construction of extended covariance matrix also is obtained. The simulation results show that the proposed method offers improved performance in the precision of DOA estimation due to the increase of virtual sensors.

The High Frequency hybrid radar mode combines sky and surface wave propagation. As all High Frequency radars, it can be impacted by ionospheric instabilities. A behavioral model able to include ionospheric spatial and temporal variations has been implemented to estimate the impact of ionospheric irregularities on radar signal processing and Doppler-distance images. In this work, probabilistic models of the ionospheric fluctuations in the ray tracing have been introduced using the phase path fluctuation only. Based on Shkarofsky's spectral power density, random variations on some parameters of Booker's electron density profile have been performed to generate disturbed electron density profiles. Afterwards, a propagation delay, integrated in the received radar signal, has been calculated in terms of phase path variation. Moreover, the temporal aspect of the ionospheric variations has been macroscopically implemented by a filtering step according to the Total Electron Content variation. Results of this simulation are presented with the corresponding statistics. Doppler and distance distributions have been computed for several filter cut-off frequency values and for different Shkarofsky's spectral power density parameters. At last, the process described above works properly: its results have been successfully compared with actual radar data for this purpose.

A wireless power transfer system is designed to power remotely placed wireless sensors using UHF band. For receiving purpose, a small and compact, bi-quad antenna isdesigned which has a fractional bandwidth of 6.89% (443.65 MHz-475.5 MHz). The receiver antenna is uni-directional and has the maximum gain of 9.7 dBi. The overall dimensions of the antenna including the reflective ground plane are 50 cm × 30 cm × 16 cm (0.767λ × 0.46λ × 0.172λ at 460 MHz). A General Mobile Radio Service (GMRS) radio license is obtained and a frequency of 462.55 MHz is used during the test measurement. The maximum achieved effective distance is 150 ft with 3.52 V, which is enough for powering most of the commercial sensors.

This paper proposes a novel RF MEMS capacitive shunt switch, which is applied in K-band (18~26.5 GHz). The characteristic impedance matching of the RF MEMS switch is achieved by discontinuous coplanar waveguide (DCPW) structure. Two actuation poles are located at the bottom of the fixed-fixed beam, and they are covered with a dielectric layer of SiN. The pole's thickness is less than that of CPW signal, to avoid the phenomenon of dielectric charging betweenthe beam and the pole. The proposed MEMS switch is fabricated on 400 μm-thickness high resistivity silicon, using the MEMS surface micromachining process. Measured results demonstrate that, at K-band, the return loss is better than 22 dB, and the insertion loss and isolation are better than 0.5 and 17 dB, respectively. The on/off switched timeis 168/54 μs when the DC bias voltage is 0/54 V. This proposed MEMS switch provides a solution for K-band communication system applications.

In this paper, a standard cell radiation pattern is selected to accelerate the synthesis of a large-scale arrays pattern. The radiation patterns distortion of each cell in array is transformed to the additive perturbation in the array manifold matrix of the antenna array, and the weighted total least squares method is developed to solve this matrix problem. The examples of several antenna arrays are presented to verify the method. Benefiting from the direct solution of matrix with the standard cell's radiation pattern, the method is low in computation cost and fast in speed.

A two-dimensional (2D) band-gap wire structure with a spatial defect has been fabricated and studied in order to demonstrate which way the violation of periodicity affects its spectral properties. We experimentally demonstrate and numerically verify the occurrence of defect modes revealed as localized resonant peak inside the band gap transmission spectrum of 2D band-gap wire structure. We also demonstrate the efficient frequency tunability of these defect mode peaks by varying defect size in the frequency range 22-40 GHz. The visualization and analysis of spatial electromagnetic (EM) field distribution within the defect of 2D band-gap wire structure is performed both experimentally and numerically. A good agreement between the experiment and numerical simulation is demonstrated.

A rectangular metallic waveguide with a chiral medium is considered in this article. The field distribution inside a rectangular waveguide is investigated. The task is considered in a full vector setting. The mixed finite element method is used to calculate the rectangular waveguide with a chiral medium.

The paper presents the results of the use of iron nanotubes as the anode material of lithium-ion batteries. To assess the degradation of the morphology of nanostructures after different numbers of cycles of life tests, the method of scanning electron microscopy, Mossbauer spectroscopy, and X-ray diffraction analysis were applied. It is shown that the decrease in discharge capacity starts at the 380th cycle and is caused by the onset of degradation processes of nanostructures due to the formation of amorphous inclusions and an increase in macrostresses and distortions in the structure. The complete degradation of the structure is observed after the 492nd life cycle test. According to the data obtained by Mossbauer spectroscopy, it has been established that an increase in life cycles leads to an increase in contribution of partial spectrum characteristic of a paramagnetic state. That indicates an increase in degradation rate of nanostructures and an increase in the content of impurity inclusions and amorphous formations in the crystal structure.

Orbital angular momentum (OAM) as a powerful candidate to enhance the spectral efficiency and system capacity by providing the new degree of freedom for multiplexing has been recently advocated in wireless communications. In this paper, we propose an OAM-based massive multiple-input multiple-output (MIMO) scheme to significantly improve the transmission performance of wireless communication system in line-of-sight scene.The uniform rectangular arrays (URAs) are used as transceivers in our system model, and the ideal OAM antenna model that is capable of providing OAM-channel independently is used as the array element. Multiple reference coordinate systems based on per transmitting antenna and the cumulative phase of specific radio vortices are used to describe the OAM-MIMO channel model. The results of numerical analysis indicate that the proposed OAM-based massive MIMO system could obtain an overwhelming capacity gain against the conventional MIMO system.

In many modern GPR systems, it is desired to detect the presence of targets in the interference which includes clutter and noise. Detection of water leaks using GPR has been aimed in this work. Pipe and soil are known as the clutter of data in this scenario. Various signal processing techniques like multivariate subspace-based algorithms are proposed to effectively suppress the clutter and increase the signal to interference ratio. Combining Independent Component Analysis (ICA) and Principal Component Analysis (PCA) as a unique algorithm has demonstrated the ability to eliminate the GPR clutter and extract the target signal.

This paper proposes a prototype of a flexible antenna which utilizes a star patch design. The work seeks feasibility of the star patch antenna to maintain its characteristic when it is bending on a curvy structure. The patch antenna is fabricated on a 0.8 mm thickness, h of polyimide film with a dielectric permittivity, εr of 3.4. The simulation result in Computer Simulation Technology Microwave Studio (CST MWS®) software shows that the antenna provides a -10 dB bandwidth of 24.9% at 2.45 GHz with a minimum reflection coefficient, S₁₁ of -27.67 dB in the flat condition. The stability in its performance has been noticed in which the shift in the resonant frequency is less than 2% when the structure is bending on a curvy surface with a radius of 90 mm. The measured results in terms of reflection coefficient, bandwidth, radiation pattern and gain demonstrate a good agreement with the simulated results.

Electromagnetic (EM) vortex wave carrying orbital angular momentum (OAM) has attracted a lot of attention in radar imaging, due to its potential capability of new degree of freedom for information modulation. Most existing OAM-based radar imaging methods require abundant OAM modes to realize the azimuth resolution. Switching between the OAM modes frequently increases the burden of radar antenna and the complexity of beam steering. In this paper, a novel electromagnetic vortex synthetic aperture radar (EMV-SAR) model with equivalent squint imaging is established.The geometrical model and echo signal model are derived correspondingly. By analyzing the echo signal model, amplitude and phase modulation introduced by the OAM aect the azimuth focusing, and traditional imaging algorithms are no longer applicable. Hence, a novel image formation method based on the traditional Chirp-Scaling (CS) algorithm is proposed for the EMV-SAR. The amplitude weighting function and phase modulation function are derived accurately, and high-precision focusing processing is achieved by modied CS algorithm. Point targets simulation results validate that the image focusing performance can be improved signicantly using the proposed algorithm.

Aimed at the deficiency of conventional parameter-level methods in radar specific emitter identification (SEI), which heavily relies on empirical experience and cannot adapt to the waveform change, a novel algorithm is proposed to extract specific features and identify in Hilbert-Huang transform domain. Firstly, 2-dimensional physical representation of emitter is formed with Hilbert-Huang transform (HHT). Based on this, 4 types of multi-view features are constructed, and the feature space is spanned by elaborating the extraction. Principal components, between-class similarity, spectrum entropy, and deep architecture are used to describe the subtle features. Finally, support vector machine (SVM) is selected as the classifier to realize identification to alleviate the small sample problem. Experimental results show that the proposed algorithm realizes specific identification using 4 intentional modulations of simulated data. The selected 4 types of unintentional representations are feasible to discriminate identical emitters. Additionally, the proposed algorithm obtains higher accuracy than typical parameter-level methods in the signal-to-noise ratio (SNR) range [0, 20] dB.

In this paper, we propose a transmissive quarter wave plate (QWP) which can provide linear-to-circular polarization conversion in terahertz (THz). The structure is composed of one dielectric layer with staggered split ring resonators (SSRRs) on both sides. The simulation results show that the proposed structure can offer a nearly pure left circularly polarized wave with 3 dB axial ratio bandwidth of 0.337 THz; meanwhile, the bandwidth of polarization conversion efficiency beyond 80% reaches 0.170 THz. Additionally, the distributions of surface currents and electric field are discussed to explain the physical mechanism of the proposed structure. The linear-to-circular polarization conversion can be attributed to the inductance effect and capacitance effect between SSRRs. Finally, we validate the performance of the proposed THz-QWP. Such a device could potentially be used in THz communications, THz imaging, and THz sensing.

High-altitude electromagnetic pulse (HEMP) field tests are often conducted in the working volume of HEMP simulators to verify the hardness or HEMP survivability of the systems under test. For HEMP field tests, enough confidence should be provided through certain specific test designs. In this paper, the confidence probability of HEMP field tests is defined through a statistical analysis. Based on this definition, the confidence level of the tests is proposed to address the problem that the probability of a failure or significant upset is unknown. The relation between the number of repeated illuminations in one test status and confidence level is provided after analysis. By balancing cost and confidence level, an appropriate number of the repeated illuminations for each test status can be obtained. The comparison with the definition in another article is also made.

In this paper, the sea surface wind speeds are retrieved by using an analytical scattering model, so called the analytically-based geophysical model function (GMF), from C-band Sentinel-1A VV-polarized synthetic aperture radar (SAR) images. The analytical models accurately simulate the rough surface scattering in the incidence angles range of SARs. The accuracy of the scattering results of the models depends on the sea wave spectrum. In this work, the effect of the sea spectral models on the accuracy of the sea surface wind speed retrieving is evaluated. In this regard, for omnidirectional and directional parts of sea spectrum, the Elfouhaily/Hwang spectra and Elfouhaily/McDaniel's models are employed, respectively. The VV-polarized backscattered normalized radar cross-section (NRCS) is calculated by using the first-order small-slope approximation (SSA1) with the four composite models of the mentioned omnidirectional spectra and angular spreading functions (directional part), and the backscattering results are compared with the empirical model CMOD6. Then, from the VV-polarized Sentinel-1A SAR data in two resolutions, the wind speeds are estimated by the analytical and empirical models. The comparison of analytical models with CMOD6 shows that Hwang-Elfouhaily model is the best among the composite models. The results show that the analytical scattering models can be easily used for the sea wind speed retrieving below 20 m/s.