We propose the design of a dual-band nano-structured polarizer that allows the transmission of two different linear polarizations within different frequency bands. A broad-band transmission window in the visible range exists for the x-polarization, whereas the y-polarization transmits efficiently in the near-infrared range. The transmittance exceeds 80% for the target polarization in both cases under normal incidence. This operation is achieved by an orthogonally patterned metallic surface having a long metal wire along the x-axis with four other small metal wires along the y-axis and allowing for a strong localized slit resonance to operate in the desired passband. The appropriate metal length and air gap choice lead to intense slit resonances in the spectral region of choice. The proposed design can be optimized for either ultrawide single band operation or dual-band perpendicular polarization operation.

In this paper, a novel dual-frequency circularly polarized (CP) antenna applied to BDS system is presented. CP radiation is achieved by etching slotted circular patches of complementary open-loop resonators, which are excited by a feeding network consisting of a double-layer power divider. The circular patch is miniaturized by a complementary split-ring resonator (CSRR) etched on the patch. The overall dimension of the antenna is only 0.32λ₀×0.32λ₀×0.0104λ₀, where λ₀ is the corresponding free space wavelength at 1.268 GHz. The proposed antenna has 50 MHz (1.25-1.30 GHz) and 60 MHz (1.53-1.59 GHz) impedance bandwidth and 20 MHz (1.25-1.27 GHz) and 20 MHz (1.55-1.57 GHz) axial ratio bandwidth, respectively. The antenna profile is low, which is easy to install. Because of these performance indexes, the antenna has superior practicability in BDS system.

Contactless identifying different life states can result in improved rescue strategies in post-disaster rescues (such as earthquake and mine accident). If the buried targets are identified extremely endangered with very poor life states, the rescuing principles should be time first. Conversely, if the life states of the buried targets are relatively good, more reliable and safer methods should be given priority although they may cost a little more time. Unfortunately, there are few corresponding reports in life states identification, and current researches mainly focus on detecting or locating under penetration condition. This paper conducts a research on the change laws of physiological parameters of six New Zealand white rabbits, 3 females and 3 males. Experimental condition is under water and food deprivation to simulate one of the typical trapped situations of buried targets in post-disaster rescuing missions. Respiration is synchronously detected by an ultra-wideband (UWB) system in non-contact and an RM6240E system in contact. Heart rate, weight, and anal temperature are measured in contact measurement meanwhile. Over the time under water and food deprivation condition, there are typical and regular varieties in the respiration waveforms and heart rate values, which provide the possibility to identify different life states. Particularly, the respiration waveform changes in UWB radar signals are envisioned to be applied in practical post-disaster rescue where only UWB radar can penetrate ruins through penetrating measurement method.

The present work demonstrates the design of a wideband 2×1 reconfigurable beam steering array for wireless communication systems. The designed antenna is powered by a microstrip line, and consisting of a two rectangular-shaped radiating elements and a rectangular planar ground. Its dimensions are the following: 0.67λ₀ x 0.53λ₀ x 0.03λ₀. It executes three reconfigurable operating states by turning on and off two PIN diodes to change the direction of the main beam, as well as a beam tilt ranging from (±30°) to (±38°). A progressive analysis in order to enhance the the antenna characteristic performances is furnished. The proposed reconfigurable antenna bandwidth is 18.18% (simulated), 18.84% (theoretical) and 19.42% (measured). The presented antenna has a maximum gain of 8.62 dB (simulated) and 8.45 dB (measured), and a higher efficiency ratio of 80% to 86% over the operating band (5 GHz-6 GHz). The designed antenna is fabricated using a low loss Rogers RT5880 substrate of 2.2 relative permittivity. The simulated, theoretical and measured results are presented and exhibit good accord, including the S₁₁ parameter and radiation patterns. In addition to the pattern reconfiguration, the obtained results are useful in order to improve the overall gain, antenna bandwidth and efficiency.

The electrical representation of the contactless power transfer (CPT) system with a coaxial transformer for the power traction in the rotary drilling system is presented. The air gap in the rotary transformer can lead to a lot of leakage inductance, so that the series-series (SS) compensation capacitors are used to increase the efficiency and the capability of the system. Moreover, the frequency response of the SS compensated CPT system is analyzed, and the transfer characteristics of the CPT system are revealed at different resonant frequencies. It is shown that the phase angle of the input impedance at resonant frequency determines the operation mode of the CPT system. At resonant frequency ω₀, the system can operate in constant-current (CC) mode, whereas at resonant frequency ω_H, it can work in constant-voltage (CV) mode. In the application of the drilling system, the CV mode owning good load regulation is more preferred than the CC mode for a wide range of load variation. At last, the analysis result is verified by experiment. The experimental results indicate that the CPT system in the CV mode can produce a 30~35 V voltage output and can transfer maximum power 180 W with an efficiency of 78.5%. The proposed CPT system can well meet the requirement of power supply in the drilling system.

In this work, a high-gain and wideband microstrip-fed slot antenna is proposed and investigated, which is composed of an anisotropic metasurface (AMS) and an aperture coupled structure. The proposed microstrip antenna with four resonances can be obtained by merging the AMS with an anomalous inverted π-slot feed structure in a low profile (1.07λ₀×1.07λ₀×0.06λ₀). The simulated results indicate that the proposed microstrip antenna can achieve a wide impedance bandwidth of 56.1% from 3.32 to 5.91 GHz, which is verified by experiment. In addition, the measured results show that the peak gain of the proposed microstrip-fed slot antenna is 10.7 dBi at 5.3 GHz, and the relative bandwidth of 3-dBi gain is 42.2% from 3.85 to 5.91 GHz. Compared with previous works, the proposed design has a lower profile while achieving a much wider operating bandwidth, where the four controllable resonance modes offer more possibilities for band expansion. This work shows potential application in integration with high data rate systems.

Through-Wall-Imaging (TWI) radar offers considerable advantages for applications that require safety and security, such as disaster survivor rescue and tracking terrorist activities. In such situations, the use of an impulse UWB radar system is constantly increasing due to its ability to provide precise images of hidden targets in a short period of time. This paper presents a new radar system for through-wall imaging using an impulse-radio ultra-wideband (IR-UWB) signal. The radar system is built using a field-programmable gate array (FPGA) board, an oscilloscope, and Vivaldi antennas. The radar system transmits impulse signals, which have a monocycle shape with a 400-picosecond duration and a 4.6 GHz bandwidth. The FPGA board is used to produce impulse signals that have a short time duration in the sub-nanosecond range in order to expand the bandwidth of the generated signal and make the developed radar capable of providing high-resolution images. The FPGA-based implementation of the IR-UWB generator offers the flexibility to modify the spectrum characteristics of the generated signal. The receiver side of the radar system collects the echoes using the principle of synthetic aperture radar (SAR), and then the time-domain back-projection algorithm is applied to the radar echo to form 2D images. An indoor imaging experiment was carried out with two human targets to investigate the imaging capability of the designed IR-UWB radar. The obtained experimental results demonstrate that this radar has the potential to deliver high-resolution images of multiple human targets and identify their locations.

This paper investigates the electromagnetic coupling from various aperture shapes in aperture coupled suspended rectangular microstrip antennas. The proposed study involves various shapes of coupling aperture such as ``rectangle'', ``H'', ``bowtie'', and ``hourglass'' with a single-layer aperture coupled suspended rectangular microstrip antenna. Among the various shapes, ``hourglass'' shaped aperture yields maximum coupling leading to maximum bandwidth. For the validation aperture coupled suspended rectangular microstrip antenna with ``hourglass-shaped'' aperture is fabricated, and measurements were carried out. The measured fractional impedance bandwidth (FBW) with ``hourglass'' aperture is more than 30% at 1.06 GHz. Measured peak gain and front-to-back (F/B) ratio of aperture coupled suspended microstrip antenna with ``hourglass'' at 1.06 GHz are 8.5 dBi and greater than 11.2 dB, respectively. The influence on the antenna's performance parameters such as realized gain, impedance bandwidth, and F/B ratio due to metallic mounting surface is also investigated. The simulated and measured performances of the antenna are in agreement. The proposed investigation is very useful for various applications, when broadband antenna is mounted on a metallic body.

In this article, a miniaturized antenna with a Koch fractal defected ground structure (KFDGS) is proposed for C/X and Ku-band applications. The performance of an inset-fed lambda/2 patch antenna is examined using an iterated KFDGS etched on the ground plane. A conventional antenna operated at 16 GHz with a return loss of -34.31 dB is constructed, followed by a tri-band miniaturized antenna operating at 6.35, 9, and 13.05 GHz with a return loss of -22.41, -25.05, and -28.54 dB in order to achieve miniaturization of 60.31%, 43.75%, and 18.43% respectively. An antenna is designed on a Roger RT Duroid substrate, fabricated, and tested with dimensions of 12×14×0.8 mm³, and its impact on reduction in size performance has been evaluated with measured peak directivity and gain of 3.07 and 2.80 dBi at 6.35 GHz, 4.78 and 4.65 dBi at 9 GHz, and 7.73 and 7.76 dBi at 13.05 GHz, respectively. A good agreement is found between the measurements and simulations.

In this paper, a design method for near-field focusing cylindrical holographic impedance metasurfaces is proposed. Firstly, based on the design theory of planar holographic impedance metasurface, we deduce the design formula for cylindrical holographic impedance metasurface by using the method of major axis matching. Then the feasibility of theoretical analysis is verified by simulation and measurement. The results show that the design method can effectively realize the near-field focusing, which can provide a reference for the application of conformal devices for microwave hyperthermia and energy harvesting.

A simple electromagnetic system composed by a Schottky barrier diode (SBD) and linear lossless microstrip line is introduced in this paper. The period doubling phenomenon in this circuit system is studied following the train of thought, which is adopted in the field of the driven Resistor-Inductor-Diode (RLD) series circuit. The related phenomenon and its origins have been studied extensively in RLD circuit. However, it will not be able to exhibit period doubling and chaos if SBD is applied in RLD circuit. We show period doubling phenomena in a microwave circuit containing SBD for the first time. This paper reveals that the given circuit can produce cycle period doubling at microwave frequency by means of simulations and experiments. Physical verification and theoretical explanation have been given in this paper.

The retrieval of soil moisture in presence of vegetation has received relatively less attention than bare land when observations are made with Global Navigation Satellite System (GNSS). In plane bare land, the reflected GNSS signal is affected by the land characteristics which is dielectric constant of soil. However, in vegetated land, the reflected signal is affected by dielectric constant of soil as well as the characteristics of vegetation which makes the retrieval of soil moisture a cumbersome task in presence of vegetation. Monitoring soil moisture in vegetated land is important for soil health and its suitability for agriculture purposes. Therefore, analysis of soil moisture in presence of vegetation has been studied in this manuscript by utilising the Navigation with Indian Constellation (NavIC) which is a very new entry in GNSS domain by Indian Space Research Organization (ISRO). NavIC receiver setup was installed in a wheat agriculture land situated in Dehradun, India. The wheat crop was sown in the month of November, and it was harvested in the month of April. In situ measurement of soil moisture, crop height, humidity, soil temperature and air temperature were made. Fixed frequency method and Lomb–Scargle Periodogram (LSP) method have been analysed to determine the sensitivity of soil moisture in presence of vegetation. 15° to 30° elevation angle was utilised in the study. The sensitivity analysis was carried out by categorizing the crop based on crop height. Three crop categories have been considered which are 0 to 20 cm, 20 to 80 cm, and greater than 80 cm. The correlation coefficient in the first stage of crop growth using the fixed frequency method was 0.76, which decreased to 0.42 in second stage of crop growth and finally to 0.35 in final stage of crop growth. The correlation coefficient using LSP method was -0.68, -0.65, and -0.50 for the first, second, and third stages of crop growth, respectively. It was observed that for lower crop height (< 20 cm) fixed frequency method is more useful than LSP method. However, for higher crop height (> 20 cm) LSP method is better suited.

In the research of radar-based human motion classification and recognition, the traditional manual feature extraction is more complicated, and the echo dataset is generally smaller. In view of this problem, a method of human motion recognition in small sample scenarios based on Generative Adversarial Network (GAN) and Convolutional Neural Network (CNN) models is proposed. First, a 77 GHz millimeter wave radar data acquisition system is built to obtain echo data. Secondly, the collected human motion echo data is preprocessed, the micro-Doppler features are extracted, and the range Doppler map (RDM) is used to project the velocity dimension and accumulate the two-dimensional micro-Doppler time-frequency map dataset of the human motion frame by frame. Finally, the deep convolution generative adversarial network (DCGAN) is constructed to achieve data augmentation of the sample set, and the CNN is constructed to realize automatic feature extraction to complete the classification recognition of different human motions. Experimental studies have shown that the combination of GAN and CNN can achieve effective recognition of daily human motions, and the recognition accuracy can reach 96.5%. Compared with the manual feature extraction, the recognition accuracy of CNNs is improved by 7.3%. Compared with the original data set, the system recognition accuracy based on the sample augmentation data set is improved by 2.17%, which shows that the GAN has an excellent performance in human motion recognition in small sample scenarios.

In this paper, a modified magnitude-selective affine function-based behavioral model is proposed for the linearization of power amplifiers in multiple-input multiple-output (MIMO) systems. In this model, high-order polynomials in the crossover memory polynomial (COMPM) are replaced by magnitude-selective affine functions to compensate for the crosstalk and nonlinear distortion, leading to a highly efficient hardware implementation. The performance of the model is validated using two 3-carrier long-term evolution (LTE) signals of 20 MHz bandwidth. Experimental results show that the proposed model can achieve nearly the same adjacent channel power ratio (ACPR) and normalized mean square error (NMSE) as COMPM with about 70% reduction of hardware complexity.

The properties of the angular glint of radar reflections from the propeller hub are considered. Analytical expressions were obtained based on a known multipoint geometric model of the propeller hub to calculate the probability density function parameters of angular glint for the planes, azimuth, and elevation angle for a single-blade rotor at an arbitrary rotation angle of the head. The relations obtained for a propeller hub with a single blade are generalized to the case of a propeller hub with an arbitrary number of blades. It is shown that the angular glint of the propeller hub is a random process with periodically changing parameters. The theoretical results are confirmed by mathematical modeling.

In this paper, we propose a phase compensation method for cylindrical reconfigurable reflectarray antennas and design a cylindrical reconfigurable reflectarray antenna (CRRA) for generating steering beams. Using a PIN diode loaded reflectarray element, 1-bit reflection phase-shift with phase difference of 180°, can be realized. The cylindrical reflectarray consists of 16×18 unit cells whose reflection phase shifts are controlled by bias network independently. Using phase quantization, the reflectarray can generate the desired phase distributions for steering beams. Both simulated and measured results show that the proposed CRRA can achieve beam scanning in ±40˚ angle range. In addition, the measured gain reaches 20.5 dBi, and 1 dB gain bandwidth is 6.9%. The proposed cylindrical conformal reconfigurable reflectarray antenna can provide a reference for the application of the conformal scenario of a reconfigurable reflectarray antenna in the future.

Finite-aperture microwave vortex beams of various structures in the near-, middle-, and far-field propagation zones have been simulated. The decay of external sidelobes leading to the end of non-diffractive propagation within a fraction of the near-field zone is observed. A ring source of the vortex beams with phase-shift and frequency-sweep control of angular modes and polarization patterns through the use of patch antenna arrays of varying polarization is suggested. A new form of the beam wavefront variation with azimuthal undulation has been proposed that allows one to significantly diversify and dynamically control the beam structure. The consequences of a limited number of antenna patches in a circular array have been considered. The effects of a gradual drop of radiation power along the array and the use of multiple feed points for improving the beams have been simulated.

This letter, an ultra-wideband compact printed log periodic dipole (LPD) array antenna is designed to operate between 500 MHz and 6 GHz frequencies. The proposed LPD antenna structure consists of one bow-tie dipole and 15 regular dipole elements. The bow-tie element is introduced to improve the antenna's performance at the lowest frequencies below 1 GHz and at the same time to reduce the antenna size maintaining a good performance. An experimental antenna prototype has been designed, optimized, fabricated, numerically and experimentally assessed. The obtained results are very promising, and they demonstrated that the presented antenna prototype is able to operate in the range between 500 MHz and 6 GHz with an average gain of 6 dBi and a very compact size.

While analyzing wideband electromagnetic scattering problems using ultra-wideband characteristic basis function method (UCBFM), the reconstruction of a reduced matrix and the recalculation of an impedance matrix at each frequency point cost a large amount of time. To overcome this issue, a novel method that combines UCBFM with compressive sensing (CS) is proposed in this paper to rapidly analyse the wideband RCS. The proposed method makes the ultra-wide band characteristic basis functions (UCBFs) generated at the highest frequency as the sparse basis, introduces the CS theory, randomly extracts several rows from the original matrix as the measurement matrix, utilizes the corresponding excitation vector as the measurement value, and then employs the recovery algorithm, through which the solution of target induced current can be obtained. Due to partial filling of impedance matrix and efficient recovery algorithm, the wideband RCS computation time of the object is significantly reduced using the proposed method. Furthermore, the numerical simulation results show that the computation efficiency for the target wideband RCS can be further enhanced compared with that of the stand-alone UCBFM.

This paper presents a design of a right hand circularly polarized x-band reflectarray antenna (RA) at a center frequency 12 GHz. The reflectarray is fed by a linearly polarized dipole antenna. The proposed reflectarray antenna can be used for CubeSat applications. The reflecting elements have the shape of a pentagon. This shape is chosen to convert the incident linearly polarized fields to the required circular polarization. A dipole antenna is used as linearly polarized (LP) feeding element for the proposed reflectarray. This dipole antenna is tilted w.r.t the x-axis by an angle 45˚ to introduce nearly equal polarizations in x and y directions on the aperture of the reflectarray. Each reflecting element is adjusted to produce a phase shift 90˚ between the reflection coefficients in x and y directions. The required reflected phase is realized by adjusting a scaling factor (SF) for the pentagonal patch in x direction to the corresponding SF in y axis. This phase difference is responsible for polarization conversion of the incident plane wave into circularly polarized reflected wave. The reflectarray is designed with focal to-diameter (F/D) ratio equals unity. In this work, an efficient technique is discussed for modelling the reflectarray designed. This technique is based on developing a Visual Basic Script file for allocating the reflecting elements with their corresponding dimensions in their location on the simulation tool. This script file is used directly by the simulation tool (HFSS) to draw the complete model automatically. This procedure has a significant role on simplifying the modeling of complicated structure like the proposed reflectarray. The proposed reflectarray antenna is simulated at 12 GHz. The obtained axial ratio (AR) is found to be 2.1 dB, and peak gain is 18 dBi. The antenna is also fabricated and measured for verification.