In this paper, an iterative algorithm for the location of multiple sources based on independent doublets arrays is proposed. The array brings a unified signal model for both near-field and far-field incoming sources. The signal model refrains the bias of Fresnel approximate due to the close displacement between elements of each doublet. Only exploiting the geometry of each doublet in direction-of-arrival (DOA) estimation, the proposed algorithm can avoid synchronization technology among different local oscillators of doublets, which means that elements among doublets could be independent. The proposed algorithm employs all the data received by the independent doublets arrays and can deal with more than two sources with only two coherent sensors in each doublet. The algorithm provides a simple approach and obtains acceptable results. Simulation results are illustrated to verify the effectiveness of the proposed algorithm.

Dual-rotor permanent magnet motor has the characteristics of high torque density and high efficiency and has a wide range of application prospects in many fields. However, the double air-gap structure also makes the internal magnetic field distribution more complicated and torque fluctuation more serious. To improve the double-layer air-gap magnetic field distribution and reduced torque pulsation, based on the Halbach array magnetization, the inner and outer irregular Halbach array dual-rotor permanent magnet motor model was established to obtain the ideal one-sided magnetic field. By comparing the magnetic field distribution of the inner and outer layers, the no-load back-EMF, and the cogging torque, it is proved that the motor with the proposed structure can optimize the air-gap magnetic density and no-load back-EMF and reduce the cogging torque; at the same time, the torque ripple is also significantly reduced to ensure the stability of the motor operation.

This article is about the characterization of a 3D metamaterial structure arranged to reinforce the surface wave radiation of antennas relevant to High Frequency (HF) surface wave radars. The use of a corrugated surface with a negative equivalent permittivity placed in the vicinity of the antenna increases the surface wave component of the radiated field. In order to confirm the anticipated performance of that metamaterial antenna, near-field measurements have been realized. Also, an original near far-field transformation technique, taking the surface wave into account, is applied to derive the radiation pattern of the antenna. Measurements were first achieved at reduced scale in UHF band and at full scale in HF band. At 1.1 GHz, they were operated on a small scale mock-up in a semi-anechoic chamber. An electric field acquisition setup installed in an Unmanned Aerial Vehicle (UAV) is used to characterize this antenna under outdoor conditions. This measuring system was especially designed for this application. The obtained results are discussed and enable us to validate the expected behavior of the antenna.

This article presents a T-Shaped Tri-Band (TSTB) antenna based on the Characteristic Mode Analysis (CMA) for satellite applications. Tri-band characteristics are achieved by exciting two orthogonal radiating modes for the L5-band and L1-bands, and one higher order radiating mode for the S-band. Initially, cavity model theory is applied to a rectangular antenna to calculate orthogonal modes (TM^z₀₁₀ & TM^z₀₀₁) at L5-band and S-bands, and these modes are validated using the CMA method. With the help of surface current study and modification of a rectangular antenna, the one higher order radiating mode and orthogonal modes are excited by using the CMA method. All desirable radiating modes are excited by a single coaxial feed line in full-wave simulation, which is based on FIT (Finite Integration Technique). The proposed antenna's measured operating frequencies are 1575 MHz (L1-band) for GPS (Global Positioning System) system, 1174 MHz (L5-band), and 2495 MHz (S-band) for IRNSS (Indian Regional Navigation Satellite System) applications, and corresponding impedance bandwidths at S₁₁ ≤ -10 dB are 24 MHz (1563-1587 MHz), 24 MHz (1164-1188 MHz), and 51 MHz (2484-2535 MHz), respectively. The proposed antenna layout is printed on low-cost FR4 material and exhibits good agreement between simulated and measured results using CST and HFSS EM-tool. The proposed antenna is single feed, low profile, and economical with stable broadside radiation patterns along with good gain.

This paper discusses the variation of ionospheric Total Electron Content (TEC) over low latitude Indian region, Hyderabad station (Lat: 17.39^oN, Lon: 78.31^oE) for geomagnetic quiet and disturbed days during the low solar activity period (2017 year) of the 24th solar cycle using global ionospheric models and experimental NavIC (Navigation with Indian Constellation) data. The work mainly focuses on the performance of the IRI Plas 2017 (International Reference Ionosphere) model with and without assimilation of TEC input, GIM TEC (Global Ionospheric Maps) and IRI 2016 models. In order to evaluate the performance of the models, the diurnal, monthly, and seasonal variations of Vertical TEC (VTEC) are predicted and compared with Indian regional NavIC data. From the result analysis it is observed that smaller Root Mean Square Errors (RMSEs) between NavIC VTEC and modelled VTEC are found in June and December solstice months than March and September equinox months. The VTEC predicted by the IRI Plas with assimilation of TEC input option produced smaller estimation errors than IRI Plas without assimilation of TEC input and IRI 2016 model. The same analysis has been tested for geomagnetic storm occurred during 7-9 September, 2017 for different locations. The IRI Plas 2017 with TEC input option exhibits better performance than IRI Plas and IRI 2016 models. Therefore, the VTEC predictions by assimilation of optional inputs will be helpful in applications of ionspheric studies to predict the dynamics in the ionosphere particularly for the period of disturbed geomagnetic conditions.

A multi-band cylindrical conformal endoscopy antenna with low specific absorption rate (SAR) is designed for endoscope applications, which covers the Industrial, Scientific and Medical bands (ISM 902-928 MHz, 2.4-2.4835 GHz), Medical Device Radio Communications Service band (MedRadio 401-406 MHz) and Wireless Medical Telemetry Service (WMTS 608-614 MHz). The proposed antenna radiates as a symmetrical meanderline structure with a center loaded parasitic opened-loop element, which is bent into the cylindrical conformal shape and wrapped onto the inner wall of the capsule shell. The parasitic opened-loop element excites low frequency resonance at 403 MHz and reduces the SAR values of the antenna. The measured relative bandwidth (|S₁₁| < -10 dB) of the antenna implements 133% ultra-wideband, ranging from 0.35 GHz to 1.76 GHz, and 39% wideband, ranging from 2.01 GHz to 3 GHz. The peak gains and the peak 1 g SAR values at 403 MHz, 611 MHz, 915 MHz, 2.4 GHz are -26.6 dBi, -18.9 dBi, -11.8 dBi, -11.3 dBi, and 83, 82, 94, 153 W/kg, respectively. The results indicate that the proposed antenna complies well with the human safety standards.

In this paper, a direct instantaneous torque control (DITC) optimization scheme based on adaptive dynamic hysteresis (ADH) strategy is proposed for switched reluctance motor (SRM) drive system. This method can further improve the torque tracking accuracy, reduce torque ripple and solve the problem of smooth transition between SRM phases. According to the torque generation characteristics and hysteresis rule of DITC, the traditional hysteresis rule is modified, and the sampled discrete torque slope data are compensated online. Taking the slope curve after compensation as the standard, the upper and lower limits of the hysteresis controller are assigned to achieve the control effect of hysteresis dynamic regulation. The effectiveness of the method is verified by simulation under diferent operating conditions.

A new design of broadband cavity-backed slot antenna (CBSA) based on substrate integrated waveguide (SIW) technology is presented in this paper. An entire proposed antenna is printed on a Rogers RT/Duroid 5870 substrate, which consists of the SIW cavity, bow-tie slot, microstrip line feed. The proper position and size of the bow-tie slot on top of the SIW cavity will generate the cavity modes, which can be merged to obtain the broadband response. Moreover, to understand the effects of the geometric dimensions of the broadband antenna on S₁₁ are examined using parametric study. The final antenna configuration operates on a frequency band ranging from 9.25 GHz to 10.5 GHz with a fractional bandwidth of about 12.65% for the simulation part. The measured bandwidth for S₁₁ is about 12.1% (9.3 GHz to 10.5 GHz). The proposed antenna has a good measured gain of 6 dBi and 6.6 dBi, at 9.55 GHz and 10.35 GHz, respectively. The gain, the reflection coefficient, and the radiation patterns of the fabricated antenna are measured and indicated a very good agreement with simulations.

In this paper, an S/C/Ku triple-band (TB) dual-polarization (DP) shared aperture array (SAA) with an approximate frequency ratio of 1:1.8:4.5 is proposed. An S/C dual-band dual-polarized (DBDP) perforated patch antenna is designed as a shared element, and the S-band array consists of S-band-working shared elements. The C-band array interlaces with C-band-working shared element and C-band cross-patches with phase compensation. The Ku band array consists of dual-polarization rectangular dielectric resonator antennas (DRAs) for its small section area and high design freedom. In order to ensure the symmetry of the structure, all the ports adopt a vertical welding structure. A 1 × 3 prototype array is fabricated and measured, showing that the S-, C-, and Ku-bands obtain the bandwidths of 2%, 2.1%, and 1.8%, respectively. The polarization isolation is better than 20 dB in all three bands, while the cross-polarization is lower than -20 dB. The proposed array has the advantages of low cost and high integration; moreover, the proposed array owns excellent potential for expansion to large aperture benefited from its symmetry.

This paper proposes a design method of vertically polarized VHF high-gain antenna, a four-element array form. Our design improves the overall gain of the antenna and reduces its loss. In our design, the conventional impedance conversion methods are abandoned. Instead, we directly use transmission lines for impedance match which greatly reduces the loss of the antenna in the frequency range of 150 MHz-300 MHz, ensuring that the antenna provides a higher gain, and its signal transmission efficiency is also improved.

The article presents the design of an Ultra-Wideband (UWB) annular ring antenna which operates over 1.5 GHz to 12 GHz and covers most of the bands of mobile communication (GSM 1800, 1900 and 2100, UMTS, Bluetooth (2.4 GHz), WLAN 2.4/3.5/5 GHz and WiMAX 2.5/3.5/5.5 GHz). The antenna size is 40 x 36.67 x 1.6 mm³, and an FR-4 substrate of permittivity 4.3 with loss tangent of 0.025 is used for fabrication. Circular defect in ground plane of annular ring is used to achieve UWB characteristics. A wideband mushroom type Electromagnetic Band Gap (EBG) unit cell is designed which resonates at 2.3 GHz, and 8-unit cells are placed close to feeds of annular ring patch where current density is more for 2.4 GHz so as to reduce surface waves and ultimately to lower Specific Absorption Rate (SAR). SAR is evaluated with dual-feeds for single element and is lowered up to 83.64% for 1-gram of tissue mass.

In this paper, a low-profile fractal antenna with square ring slots is reported. The newly proposed fractal antenna includes circular ring radiating elements with orthogonally placed square shape slots to achieve ultra wideband operation. The compact antenna (32 × 28 × 1.6 mm³) is designed and fabricated on an FR4 dielectric substrate, and measurements are performed in the laboratory environment. The simulated and measured results demonstrate that the antenna has -10 dB impedance bandwidth of 9.4 GHz from 4.2 to 13.6 GHz in the ultra-wideband frequency. The measurement results reveal that the antenna has broadband radiation characteristics with peak gain of 5 dB in the desired band of operation. The proposed antenna has low cross polarization of -28 dB and radiation efficiency about 88% in the operating bandwidth. The large bandwidth, low cross polarization, and stable radiation characteristics of the proposed antenna confirm that the antenna may be suitable for ultra-wideband applications.

In this work, we give a theoretical demonstration of the possibility to realize a photonic demultiplexer. The demultiplexer consists of Y-shaped waveguides with one input line and two output lines. We consider a demultiplexer composed of a segment and two asymmetric resonators, grafted at the same position in each channel. This system creates the resonance modes that have a maximum transmission rate and low Q quality factors. To improve these results, we take each output line consisting of a periodicity of segments and grafted at its extremities by a single resonator. Such a system creates passbands separated by band gaps. On the other hand, the presence of a resonator defect in the middle of each output line allows us to create defect modes inside the gaps. The results show that our proposed demultiplexer system manages to separate two incoming mixed signals of frequencies f₁ = 204.75 MHz and f₂ = 208.75 MHz and guide each one of them into two different channels.

A Clown-shaped patch antenna for super wideband applications is presented. The radiator is placed on a 1.6 mm thick, RT/Duroid 5880 substrate and is fed using a 50 Ω symmetric coplanar waveguide. The size of the proposed antenna is 26 × 27 mm² (0.256λ_L × 0.266λ_L, where λ_L is the wavelength at the lower band edge frequency i.e. 2.96 GHz). The radiator is a combination of an ellipse, a rectangle, and a triangle. An impedance bandwidth of 2.96 GHz to more than 100 GHz (i.e. more than 33.78:1 ratio bandwidth) is achieved. Nearly-omnidirectional radiation patterns with an average gain of 6 dBi are achieved. A fractional bandwidth greater than 188.5%, a size reduction of ~97%, and a comparable bandwidth dimension ratio of 2768 are achieved. The investigated antenna has additional advantages like compactness, planar geometry, and super-wide bandwidth.

The aim of this study is to provide a topological optimization method for ship detection in synthetic aperture radar (SAR) imagery. The method consists of three steps: pre-processing, sparse representation and classification. For the first step, the variational model is used for SAR image filtering. For the second step, the curvature of the surface manifold is constructed for sparse representation of target. For the third step, the topological derivative method is adopted to locate the target. Experiments show that the proposed method is effective in reducing false alarms, and obtains a satisfactory detection performance.

A scheme for radar cross section (RCS) reduction of microstrip antenna array in wideband using artificial magnetic conductors (AMC), without compromising the radiation characteristics of the antenna array, is proposed. This design is based on the principle of passive cancellation. The novelty is that the reflection characteristics of the microstrip antenna array are also taken into consideration during the design process of AMCs. The aperiodic configuration is composed of three kinds of AMC lattices with selected dimensions and is applied to the design of microstrip antenna array for the purpose of RCS reduction. The simulated results show that the monostatic RCS is reduced over a wideband from 15.2 to 35 GHz (about 79% relative bandwidth), covering the operation band (20-20.75 GHz) of the antenna array. In addition, compared with the periodic configuration, it has about 4 dB lower maximum bistatic RCS.

In this article, a 28 GHz endfire antenna based on ball grid array (BGA) packaging is proposed for the 5G mmWave new radio (NR). The antenna is composed of a pair of dipole patches fed by a substrate integrated waveguide (SIW). Besides, quasi-coaxial vertical transition and transition from grounded coplanar waveguide (GCPW) to SIW are designed on the substrate to achieve compact size. The substrate is based on a single-layer printed circuit board (PCB), which can meet the cost-effectiveness requirements of the 5G application. Meanwhile, the proposed antenna can be easily integrated with other surface-mount devices by using the BGA packaging. In particular, it can be mounted near the RF front-end chipset to improve system performance. Finally, the prototype is manufactured and verified. Experimental results show that the -10 dB bandwidth of the proposed antenna is 5.35% in the range of 27.3 to 28.8 GHz, and the peak gain achieves 4.4 dBi at 29 GHz.

In high speed indoor communication, ultra-wideband (UWB) plays a crucial role. UWB contains several other narrow band systems, which give interference. In order to reject these narrow bands present in UWB system, a novel multilayer step via electromagnetic band gap (MS-EBG) structure to vary the band-notch of UWB monopole printed antenna is presented in this work. The proposed EBG consists of grooved substrate with step via arrangement. These grooved substrate allow for the deposition of the liquids with different dielectric constants to achieve the variations in band gap center frequency of EBG. The microstrip line based model with equivalent circuit diagram of MS-EBG is developed with experimental results using suspended micro strip line (SML) method, with different liquids like kerosene, sea water, mineral oil, without grooved substrate, etc. The simulated and experimental results show liquid sensing ability of the proposed MS-EBG structure. The application of MS-EBG to vary the band notch in UWB hexagonal monopole antenna (HMA) is also demonstrated. Simulated and experimental results show noticeable variation in the band notch center frequency with different liquids deposited in the grooved substrate. The proposed method required only liquid change arrangement to get desired band notch in UWB monopole antenna. Compared to electrical and mechanical method to get band notch in UWB monopole antenna, the proposed method works without any power supply, active devices and additional complex arrangement.

Electromagnetic properties of a planar metallic metasurface with the design inspired by Babinet's principle are numerically studied. The metasurface is constructed from a metal plate perforated by coaxial-sector apertures. It is shown that the chosen coaxial-sector apertures make it possible to obtain a wider operating range of the metasurface than those composed of apertures of other shapes (e.g. round or rectangle). Moreover, the proposed metasurface performs an efficient polarization conversion of the linearly polarized wave to elliptically and circularly polarized ones in the reflected field.

This paper presents a method for rapid microwave imaging of traumatic brain injury based on scattering parameters. The algorithm uses the integer order Bessel function and Born approximation, which converts nonlinear inverse scattering problem into linear problem. After truncated singular value decomposition, imaging can be performed without iteration. Simulations and experiments show that the algorithm can not only reduce the amount of calculation for fast imaging, but also accurately image a brain hematoma or foreign body.