The propagation equation of a Lorentz-Gauss (LG) vortex beam in biological tissues is derived. The influences of the beam parameters and the biological tissues on the spreading properties of a LG vortex beam are investigated. The obtained results are interpreted numerically and shown that the LG vortex beam propagating through biological tissues with the stronger turbulence strength will lose the dark hollow center and evolve into the Gaussian-like beam more rapidly.

A practical coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with reconfigurable dual band-notched characteristics is proposed in this paper. A cup-shaped branch is added to the grounding plate and a step impedance resonator (SIR) added to the microstrip line, which realize notch characteristics in 5.1~5.9 GHz and 7~7.8 GHz bands and realize double notch function with good radiation direction characteristics. The antenna bandwidth is extended by using CPW feeding, ranging from 3 GHz to 16 GHz with the relative bandwidth of 137%. The notch band reconfigurability is realized by integrating three switches into the cup-shaped branch and SIR. In addition, the proposed antenna has a compact size of 24 mm × 32 mm × 1.5 mm and can provide omnidirectional radiation pattern, which is suitable for UWB communication applications.

In recent years, there has been more research on the use of photonic crystals PCs in the field of detection. The application of these materials as gas sensors seems very promising, because of their miniaturization and high spectral sensitivities. The aim of this work is to contribute to the design and study of a resonant microsystem based on one-dimensional photonic crystals for applications such as optical devices with high quality factor for detecting and measuring the concentration of gas in the air. Indeed, we have proposed a gas monitoring structure. This nanosystem is formed by an alternating stack of silicon Si layers and air with a resonant nanocavity in the middle. The numerical results show that the resonance peak that appears on the Photonic Band Gap (PBG) is caused by the creation of the nanocavity within the periodic 1D structure. This resonance peak can be used as a reference for real-time detection and environmental monitoring. In addition, we theoretically studied the relevance of these photonic systems and analyzed the effect of the intrinsic and extrinsic parameters of this device on the detection performance. We have also tried to improve the performance of such a device for the effect study of the inclination variation of the radiation incidence source on the selectivity of the detector.

Radar sliding window detection processes are often used in signal processing as alternatives to Neyman-Pearson based decision rules, due to the fact that they have a simpler receiver implementation and can often be designed to maintain a constant false alarm rate in homogeneous clutter. These detection processes produce a measurement of the clutter level from a series of observations, and compare a normalised version of this to a cell under test. The latter is an amplitude squared measurement of the signal plus clutter in the complex domain. It has been suggested by some authors that that there is sufficient merit in the approximation of the cell under test by a distributional model similar to that assumed for the clutter distribution. This is certainly the case when a Gaussian target is combined with Gaussian clutter, or equivalently a Swerling 1 target and exponentially distributed intensity clutter. The purpose of the current paper is to demonstrate, in a modern maritime surveillance radar context where the clutter is modelled by Pareto statistics, that such an approximation is only valid under certain limiting conditions.

In this paper, a W-band single-pole four-throw (SP4T) switch for multichannel high power transceiver chipset design is proposed based on a standard commercial 100 nm GaAs power pseudomorphic high electron mobility transistor (pHEMT) technology. The process used in this work is optimized for use in power amplifier (PA) design, resulting in larger drain electrode capacitance. In order to reduce the effect of large drain capacitance for switch design, a proper series capacitor is adopted. This capacitor can not only reduce the parasitic capacitance of the turn-off state transistor but also resonate with the parasitic inductance of the turn-on state transistor to improve the isolation. As known, the short stub is adopted to compensate the remaining parasitic capacitance. For verification, a prototype is fabricated and measured. The measured results are in good agreement with the simulated ones, and it shows that the fabricated SP4T switch achieves a bandwidth of 75 GHz-96 GHz, with an insertion loss and isolation about 4.8 dB and 28 dB, respectively. The fabricated switch also realizes a Pin1 dB about 22 dBm.

Radar cross section (RCS) reduction technology has great significance in stealth and other fields. A PSO-FSP algorithm is proposed based on the particle swarm optimization algorithm and the far-field scattering characteristics of coding metasurface to obtain the optimized coding sequence for RCS reduction. According to the principle of coding metamaterial, a 1 bit cell structure is designed. Therefore, a coding metasurface is constructed by arranging the unit cells based on the optimized coding sequence. Simulation results show that, in the case of vertical incidence, compared with metal plates of the same size, the metasurface can achieve more than 10 dB of RCS reduction within the broadband range from 15 GHz to 35 GHz, and the maximum reduction can reach 36 dB. The proposed coding metasurface has been successfully fabricated and measured, and there is a good agreement between simulated and measured results.

A novel ultra-wideband (UWB) printed monopole antenna with triple band-notched characteristics is proposed in this paper. The antenna bandwidth is extended by grooving on the connecting floor and increasing the impedance transformation line, with antenna bandwidth of 3.0~11 GHz and relative bandwidth of 114%. The overall antenna size is 35 × 30 mm². The complementary split-ring resonators (CSRRs) are loaded on the UWB antenna patch with microstrip wire feed. A symmetric J gap is loaded on the bottom plate, and the spiral gap is loaded on the feeder. The triple band-notched characteristics at 3.22~3.97 GHz, 4.94~5.84 GHz, and 7.25~7.86 GHz bands are realized. The gain of the designed antenna in the notch frequency segment can be reduced rapidly to -4 dbi, while the gain of other frequency bands is above 2 dBi. Simulated and measured results show that the antenna has stable gain and good radiation characteristics in the UWB frequency range.

This paper presents an exact analytical method to compute the air-gap magnetic field of surface-mounted permanent-magnet (SMPM) motors for evaluating slotting effects accurately. Solution field regions are divided into air-gap domain, permanent magnet (PM) domain, and slot domains. The Laplace's equations or Poisson's equations of the sub-domains are contacted by boundary conditions and then solved by exact analytical method. The actual height of slot and distance between slots are taken into account in the computation. Magnetic field distributions and cogging torque computed with the proposed analytical method are compared with those issued from 2-D finite-element method (FEM), and the comparison results are consistent and show the correctness and effectiveness of the proposed analytical method.

This paper presents the enhancement of bandwidth in circular and annular ring sectoral patch antennas. The cavity model approach has been used in identifying the higher order mode resonances that are close to each other in the sectoral patches. Bandwidth enhancement centered around these higher order mode resonances is achieved through the use of either a shorting pin or a parasitic patch. The sectoral patches have been simulated using ANSYS HFSS. The optimum position of the shorting pin and the dimension and position of the parasitic patch were determined through parametric simulations on HFSS. Measurements showed that the annular ring sectoral patch with optimally positioned shorting pin achieved 6.3 percent bandwidth with a return loss performance greater than 10 dB while the circular sector patch with a parasitic patch achieved 5.6 percent.

Electromagnetic scattering from time-varying sea surfaces under right-hand circularly polarized (RHCP) wave incidence is investigated, with emphasis on exploring the influence of nonlinear hydrodynamic interactions on Doppler spectral signatures as well as on examining the polarization difference of Doppler spectra between right-hand and left-hand polarized scattering waves. The choppy wave model (CWM) is adopted for describing nonlinear hydrodynamic interactions between ocean waves, and it is constructed by adding horizontal displacements through performing Hilbert transform for a reference linear surface model. Simulation results show that Doppler spectral signatures are significantly influenced by nonlinear hydrodynamic interactions in particular in low-grazing angle regime. It is also indicated that Doppler spectral signatures show distinct polarization dependence. In addition, numerical simulations show that Doppler shift of left-hand polarized scattering wave increases obviously with wind speed increasing, whereas the Doppler shift of right-hand polarized scattering wave looks less sensitive to wind speed variations. The result is potentially valuable in remote sensing applications with Global Navigation Satellite System-Reflectometry (GNSS-R) signals.

We theoretically propose a novel achromatic optical isolator based on circular dichroism in metamaterials of twisted chains of metallic nanoparticles. The suggested optical isolator consists of an input polarizer, followed by quarter-wave plate, then a circular dichroism material, another quarter-wave plate, and an output polarizer. In contrast to the most commonly used optical isolators, the current scheme does not use magnetic field and does not change the polarization plane.

A compact multiband multiple-input-multiple-output (MIMO) antenna for WLAN applications is presented in this paper. The proposed MIMO antenna consists of two symmetric monopole radiating elements designed to operate over 2.45, 5.2, and 5.8 GHz bands. The isolation is enhanced by using several techniques such as parasitic elements and defected ground structure. The measured S₁₁ < -10 dB is obtained over 2.36-2.68 GHz and 4.81-5.95 GHz, which can cover IEEE 802.11 a/b/g/n frequency bands (2.4-2.4835 GHz, 5.15-5.35 GHz, and 5.725-5.875 GHz). The measured isolation values S₂₁ are less than -24 dB and -27 dB over the lower and higher frequency bands, respectively. The envelope correlation coefficient (ECC) of the proposed antenna is less than 0.027 and 0.005 over the lower and higher operating bands, respectively. The overall size of the proposed antenna is 50×30×1.59 mm³. The proposed antenna is a good candidate for IEEE 802.11 a/b/g/n applications.

A printed Yagi-Uda antenna with two closely-spaced driven dipole elements and truncated ground plane is presented for dual-band operation. It is designed on a low-cost FR4 substrate with a dielectric constant 4.6, loss tangent of 0.02, and thickness of 1.6 mm. The dipole, operating in the lower band (centered at 1.8 GHz), is elliptical-bow-tiein shape with rounded edges, whereas a J-shaped dipole enables its operation in the upper band (centered at 2.6 GHz). A trapezoid-shaped director is employed to achieve maximum gain over the required frequency bands. Measurements indicate that the antenna operates from 1.71 to 1.9 GHz and from 2.5 to 2.7 GHz with |S₁₁| < -10 dB. The behavior of the proposed antenna has been investigated by studying different parameters to achieve the maximum gains of 6 and 7.7 dB in LTE band 3 and band 7, respectively, with optimal size. It is found that the experimental results of the final packaged antenna agree with the simulated ones in terms of reflection coefficients, gain, and radiation patterns.

This study proposes a broadband asymmetric Doherty power amplifier (A-DPA) with a broadband matching network and an improved power combination network (PCN). A broadband matching network in the form of a low-pass filter is analyzed and applied in this work. With the narrowband characteristic of a 1/4 wavelength transmission line, an improved PCN is also analyzed and applied to decrease the impedance transformation ratio of the 1/4 wavelength transmission line and then extend the working bandwidth of the DPA. In the design process, GaN HEMTs from Cree are selected to be the main and auxiliary power amplifier transistors, and the ADS software is used to complete the entire design process. In the working frequency band of 3.3-3.6 GHz, simulated results show that the gain is approximately 13 dB when the output power is lower than 40 dBm and that the power-added efficiency (PAE) is 39%-51% within the 9 dB power back-off (PBO) region. Measured results indicate that the proposed A-DPA exhibits a 36%-45% PAE within the 9 dB PBO region. The saturated PAE is between 58% and 62%, and the saturated output power is approximately 42 dBm.

Solid state plasma antenna based on surface PiN diodes is characterized by its wide radiation range, good stealth characteristics, compatibility with traditional microelectronic technology, and dynamic reconfiguration, which has very broad application prospects in the fields of wireless communication, radar, and remote sensing. To improve carrier concentration and uniformity within theintrinsic region, a novel SPiN diode with a double-layer structure is described in this paper. This structure can compensate the concentration attenuation at the midpoint of the `i' region, which makes carriers have a more uniform distribution with high concentration, and carrier concentration within the `i' region twice of the traditional SPiN diode. A Si/Ge/Si heterojunction diode is also researched in this paper. These results indicate that a fully reconfigurable semiconductor plasma antenna based on this novel surface PiN diode is achieved to meet the currently-growing communication requirements.

A novel broadbeam aperture-coupled coplanar parasitic rectangular dielectric resonator antenna is proposed which yields broadbeam in both working planes simultaneously. The antenna consists of a main radiating rectangular dielectric element centered over a wide feed slot and two parasitic rectangular dielectric elements one on each side of the main radiating element with an optimum gap in between. The dielectric height and wide slot both play an important role in enhancing the beamwidth in two principal planes simultaneously. It is validated that inclusion of parasitic elements enhances the broadbeam bandwidth in addition to frequency bandwidth. First three azimuthal modes are excited out of which first two modes TE^x₁₁₁ and TE^x₁₁₂ are desired. The proposed antenna is compared with single element rectangular dielectric resonator antenna. To validate the proposed design, a prototype is fabricated and measured. The simulated and measured operating frequency bands of the proposed antenna respectively are 4.8 to 6.9 GHz and 5 to 6.8 GHz. The measured E- and H-plane beamwidths range from 115° to 144° and from 115° to 124°, respectively, yielding a wider coverage area.

A mixed phased array and retrodirective array providing auto tracking of the angular position of the unmanned aerial vehicle (UAV) is presented. The phase conjugation technique and complex vector multiplication are used together to find the geometric phase of each channel canceling the need to use direction finding algorithm (DOA). After generating the phase conjugated version of the received signal on each channel, its complex vector representation will be multiplied by the complex vector representation of the received signal on the reference channel. The UAV will stay on the beak of the array factor during its movement within the field of view (FOV), and a permanent high gain data link is obtained without the need of the tracking algorithm. The beamwidth of the resulted array is widened to be equal to the FOV. The computational cost of the tracking system will be reduced due to canceling the need of using the complex processing algorithms (DOA, and tracking) used in smart antenna. Direction finding algorithm, beamforming algorithm, and tracking algorithm are combined in one algorithm. The least square error pattern synthesis with nulls method is used to eliminate the predefined interference signals and add null steering ability to the resulted array. The effect of the phase errors is reduced to the case of single antenna due to including the phase errors of each channel in its complex weights. The beam pointing error is taken as a metric to evaluate the performance of the resulted array compared with the BPE of a phased array using the monopulse tracking method.

The design and calibration of high-precision analog phase shifters are crucial issues for phased arrays interferometric passive millimeter-wave imaging systems. In this paper, a high-precision analog phase shifter is presented for phased arrays interferometric passive millimeter-wave security sensing applications, which realizes analog phase shifting function by controlling high-precision DAC (digital to analog conversion) with FPGA. It is known that pre-measured phase delay of a phased array channel is a prerequisite for beam pointing control. However, since many active devices are included in phased array channel link, the phase delay would be affected by various factors such as device moving and ambient temperature. So, high-precision phase shifting of phased arrays could be achieved only by measuring and calibrating phases when all components of the system are under normal working conditions. The algorithm proposed in this paper makes it possible to measure and calibrate phases when all sub-modules are integrated into the system, and each component is under normal working state, thus effectively avoiding the errors caused by environmental changes when the laboratory-measured results are put into practical use. Meanwhile, the algorithm is tested on Ka-band phased arrays interferometric passive millimeter-wave imaging system. It turns out that the phase accuracy of phased array channel can reach 5°±1.5°, and it only takes 2 minutes to complete the phase calibrationof 256 arrays.

In this paper, we use magnetic vector potential formulation, along with equivalence principle and image theory, to solve the electromagnetic scattering of a polarized incident plane wave by a subwavelength circular aperture in a conducting screen. The underlined analytical formulation yields a closed-form solution that is accurate for any angle of incidence or polarization and valid for the near-, intermediate- and far-field regions of observation. The formulation is based on Bouwkamp's diffraction model that uses dominant quasi-static magnetic current modes to represent the governing magnetic current distribution in the circular aperture for any incident wave. Taylor series expansion was implemented on the free-space Green's function, and the individual Taylor terms were integrated analytically to produce closed-form expressions for the scattered fields in all regions. In doing so, the Gegenbauer polynomial expansion was applied in order to allow evaluation of the resulting integrals for any observation point in the lower half space. The results obtained from the proposed analytical approach were compared with data generated through a direct application of a numerical integration technique. The comparison illustrates the validity and accuracy of the proposed analytical formulation.

A miniaturized planar ultra-wideband (UWB) polygon-slot antenna with wideband-notched property is presented in this paper. With coplanar waveguide (CPW)-fed structure and miniaturized dimensions of 18.5×20.5 mm², the antenna is easy to be integrated with microwave circuitry. By using one rectangular CSRR on rectangular patch, the WLAN band from 4.8 to 5.9 GHz is rejected. By cutting off two small rectangles in the lower corners of the rectangular patch, Antenna 2 is finally proposed, and UWB impedance matching from 3.1 to 12.6 GHz is achieved. The final proposed antenna is fabricated on a low-cost FR4 substrate and measured, and the measured and simulated results show an acceptable agreement. The antenna is validated to perform good radiation properties such as nearly stable radiation patterns, high gain, and high radiation efficiency.