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.

In this paper, a localization algorithm for mixed near-field and far-field sources by an interlaced nested array is proposed. The fourth-order cumulants (FOCs) of the received data are used to construct a FOC matrix, by which the angles of all signals can be estimated. Then, an effective method is driven to separate the directions of arrival (DOAs) of near-field and far-field sources without extreme value search. The ranges of the near-field sources can be estimated by one-dimensional (1D) search. Compared with existing nested array-based algorithms, the proposed algorithm can distinguish more sources and has higher estimation accuracy. Some simulation results are shown to certify the superiority of proposed algorithm.

A miniaturized rectangle-shaped complementary split ring radiating element with an offset-fed microstrip line is reported for multiband operations. The fabricated antenna with a compact size of 19×19×1.6 mm³ is designed on an FR-4 substrate with loss tangent tanδ = 0.02 and dielectric constant (ε_r) of 4.4. Multiband and antenna miniaturization are achieved by a complementary split ring radiating element, and it produces an impedance bandwidth of 40 MHz resonance at 3.03 GHz, 40 MHz resonance at 3.66 GHz, and 1470 MHz resonance at 5.5 GHz. The passband behaviour of the complementary split ring radiating element is studied in detail for obtaining multiband abilities of the miniaturized antenna. The metamaterial property of the complementary split ring radiating element is analyzed, by which the negative permittivity (ε) existence and the new resonance frequency are confirmed. The fabricated antenna shows optimum performance at the measured radiation characteristics.

This work presents the novel design and development of a WC-281 circular waveguide terminator or termination for microwave plasma interaction experiments. Final waveguide terminator is designed by using the quad wedge of FR4, cone of resistive material Kanthal and Teflon discs. Kanthal is a composition of aluminium, chromium, and iron. Wedge shape geometry helps in gradually changing the impedance and thus decreasing the return loss, while resistive material Kanthal attenuates the field before reaching the receiving end. This makes it suitable for use as the finest microwave termination. Simulation is carried out by CST microwave studio. The final model of terminator decreases the reflection coefficient (S₁₁) up to -40 dB while reduces the transmission coefficient (S₂₁) immensely up to -63 dB at 2.85 GHz.

This paper presents a very compact quintuple band bandpass filter utilizing multimode stub loaded resonator. A single symmetric resonator is loaded with a short ended stub at the middle along with four pairs of open-ended stubs. The open-ended stubs are folded towards each other in order to make the design more compact and improve the selectivity of the bandpass filter. Because of symmetry, the circuit is analyzed with the help of even-odd mode analysis. The proposed bandpass filter operates at GSM-900, LTE2300, WiMAX (3.5 GHz), WLAN (5.4 GHz), and RFID (6.8 GHz). The operating mid frequencies of quintuple-band BPF are 0.96 GHz, 2.22 GHz, 3.58 GHz, 5.41 GHz, and 6.64 GHz, and the corresponding 3 dB Fractional Bandwidths are 36.03%, 20.95%, 7.27%, 8.57%, and 3.37%, respectively. The implemented resonator is analyzed in detail, and the formulation is developed in this regard. The proposed filter is developed based on the analysis and is simulated and fabricated. The simulation and measurement responses agree very well.

In fusion reaction, plasma parameters such as the density and temperature of electrons should be diagnosed continuously. There are various methods to diagnose plasma parameters. In these, reflectometry systems are widely used to measure the electron density and plasma physics study. In reflectometry systems, antenna plays an important role as a transmitter/receiver element. This paper presents the design of a D-band (110-170 GHz) corrugated horn antenna suitable for reflectometry system. The simulated results for antenna are compared with that of the measurements. Further, different structures are proposed to ease fabrication complexities and reduce cost.

The design of conventional stepped-impedance microstrip line low pass filter (LPF) is based on high (Z_H) to low impedance (Z_L) ratio. The width of Z_H line, for Z_H > 100 Ω, becomes critical and challenging, especially on high dielectric constant substrates. A concept of air-filled recessed ground plane below a microstrip line is introduced in this paper. The effect of dimensions of recessed ground on characteristic impedance, attenuation and propagation constant of a microstrip line are first studied. This simple approach is utilized to design the Z_H line of stepped-impedance microstrip line LPFs. Prototypes of recessed ground stepped-impedance microstrip line LPFs with Z_H/Z_L (keeping Z_L constant as 20 Ω)ratio in the range 6 to 10 are designed and developed on Rogers 4350B of height 0.508 mm with ε_r = 3.66 at 3 GHz. For LPF with Z_H/Z_L = 10, the measured 3-dB cutoff frequency (f_c) is achieved at 3.12 GHz with return loss (RL) > 12 dB and insertion loss (IL) < 0.28 dB in its passband whereas the stopband attenuation (SBA) is better than 38 dB. In comparison to recessed ground LPF, the simulated results of conventional LPF with Z_H/Z_L = 10 (critical width of Z_H line =) are as follows RL > 10 dB and IL < 1.07 dB in passband at f_c = 3 GHz. The size of recessed ground LPF is reduced by 25%, when Z_H/Z_L is increased to 10 from 6. The approach of recessed ground microstrip line avoids the fabrication issues, reduces size, and improves the performance of LPF, which in turns confirms the advantages of recessed ground over conventional microstrip line.

This paper amalgamates two uncorrelated techniques namely finite difference time domain technique (FDTD) and nonlinear autoregressive with exogenous input (NARX) neural network to achieve a faster computation of radar cross section (RCS). It generates only a limited number of FDTD data and uses them to train a NARX neural network. The data beyond this limited number for the FDTD come from the NARX prediction. Comparison of the performance of FDTD-NARX hybrid with other methods indicates good matching with better timing for RCS of electrically larger objects.

In this paper, design of a novel broadband Canonical Tetra Sleeve Cage Antenna is presented. This antenna is designed using distributed antenna matching techniques. It has canonical shaped antenna elements and coaxial sleeves. The designed antenna operates over a wide frequency range in UHF band with omnidirectional characteristics. The proposed antenna is simulated in CST Microwave Studio, fabricated, evaluated, and the results are presented. The simulated and measurement results are in agreement. It has VSWR < 1.9:1 in frequency bands 270-330 MHz and 930-1670 MHz. The maximum value of VSWR in 250-1850 MHz is 3.3:1. The measured gain of the antenna varies from 0.6 to 5.5 dBi in the frequency range of 250 MHz to 1850 MHz. The implementation of distributed matching techniques by using canonical shaped antenna elements and tetra sleeves results in reduction of the length of the antenna by 59.86% compared to the length of a half wave dipole antenna designed at the lowest frequency. The proposed antenna finds applications in defence and wireless communication systems as a transceiver antenna.

This paper presents a stacked rectangular dielectric resonator antenna design. In this structure, two sapphires having the same dielectric constant and different dimensions piled over each other have been used for designing the proposed antenna. The designed antenna exhibits two frequency bands from 7.41 GHz to 8.21 GHz and 9.11 GHz to 12.65 GHz and impedance matching of 50 ohms. The proposed antenna design is a fine choice for subterranean and rugged communication, in addition, owing to sapphires unique features viz. durability, endurance, and aversion to physical change. The antenna structure is aperture coupled. Due to the advantage of aperture coupled feed mechanism such as good isolation between antennas and feed networks it has been employed. The antenna prototype has been fabricated, measured, and tested using Vector Network Analyzer and Anechoic Chamber to validate the proposed antenna design. The simulation results obtained indicate close proximity of tested result.

This paper presents a single layer, dual polarized 2.4 GHz microstrip patch antenna based on monostatic radiator. Microstrip-T (MS-T) feeds have been used for DC isolated Tx-Rx ports. It deploys differential feeding for receive mode operation to achieve high interport RF isolation. The differential feeding acts as a signal inversion technique to suppress the in-band self interference (SI) for simultaneous transmit and receive (STAR) operation at same frequency. The implemented single layer, dual polarized, compact patch antenna provides better than 78 dB isolation between DC isolated Tx- Rx ports at centre frequency of 2.393 GHz. Moreover, the implemented antenna achieves better than 64 dB interport isolation for 10 sdB-return loss bandwidth of 50 MHz (2.37 GHz to 2.42 GHz). The measured interport RF isolation is around 70 dB for 25 MHz bandwidth (2.385 GHz to 2.41 GHz). To the best of our knowledge, these are the highest levels of RF isolation reported for single layer, dual polarized microstrip patch antenna with DC isolated ports.