This paper introduces a model and design of an innovative bandpass (BP) negative group delay (NGD) distributed circuit. The passive circuit topology under study is constituted by fully distributed elements without lumped components. The NGD passive structure is implemented as a ladder shape topology composed of distributed transmission line (TL) elements. The S-matrix model is established from TL-based equivalent Z-matrix operations of TLs with respect to the ladder geometry. As a proof of concept, a two-cell ladder prototype is designed in microstrip technology, which is simulated, fabricated, and tested. The calculated and simulated measurements are in very good agreement with the validation of BP NGD behaviour. NGD value is better than -3 ns with centre frequency between 3.56 and 3.68 GHz over more than 30 MHz NGD bandwidth being observed. The circuit operates under insertion loss better than 5 dB and reflection loss better than 8 dB. This innovative BP NGD passive circuit can be useful in the RF and microwave engineering area, for example, to reduce the signal propagation delay in the upcoming and 5G telecommunication systems.

The electrostatic sensor is a rapidly developing particle monitoring sensor. This paper applies sensor array to inverse the information carried by detected multiple charged particles precisely. It breaks through the constraint that the detailed information of particles cannot be obtained in previous studies. The proposed method can be widely applied to oil line and gas path debris monitoring. The sensing mathematical model and the finite-element model are established. A compressive sensing-based method is proposed to invert the information of charged particles. Through simulation and experimental verification, the method can accurately estimate the centroid of multiple particles, the total charge quantity of the particle cluster, the spatial position of each particle and the charge quantity carried by each particle in the multiple particles with a low error rate when the multiple particles are distributed near the pipe wall of flow channel.

In this paper, an eight-element MIMO smart antenna system consisting of two different array modules for handheld device is proposed. The system is composed of two antenna array modules. The first module is a six-element array operating in N78 (3.3-3.8 GHz) band for 5G, which achieves MIMO functions for receiving and beam scanning for transmitting. The second module is a two-element antenna array, which operates in LTE/WWAN/N78 (0.7-0.91 GHz, 1.63-2.61 GHz, 3.3-3.8 GHz) bands. To take full advantage of the existing antenna resources in the mobile device, the six elements in the first module are combined with the two elements in the second module to form an 8-element array in the overlapping N78 band. Good isolations and envelope correlation coefficients are achieved in the receiving mode by loading L-shaped slots for the combined module. The distribution of excitations for the combined array in the transmitting mode is optimized by the method of maximum power transmission efficiency to direct the beam to the desired direction with maximum possible gain, and is realized by an in-house designed beamforming controller. The impacts of the environments on the antenna array performance are investigated.

In this paper, we present a general solution for time-harmonic electromagnetic fields with its electric and magnetic fields parallel to each other (E || B fields) in source-free vacuum and demonstrate that every time-harmonic E || B field is composed of the superposition of two counter-propagating Beltrami fields. We show that every E || B field can be categorized into one of two cases depending on the time dependence of the function that describes the proportionality between the electric and magnetic fields. After presenting the mathematical definition of a Beltrami field in electromagnetism and its handedness, we perform a detailed analysis of time-harmonic E || B fields for each case. For the first case, we find the general solution for the E || B fields using the angular-spectrum method and prove that every first-case E || B field can be generated by superposing two oppositely traveling Beltrami fields with the same handedness. For the second case, we deduce the general solution for the E || B fields by employing complex analysis and demonstrate that every time-harmonic E || B field is composed of two counter-propagating planar Beltrami fields with opposite handedness.

The research goal of low-resolution radar aircraft target classification is to analyze the category of the given low-resolution radar aircraft target echo. In existing solutions, the feature extraction methods based on rotating modulation spectrum have good performance, such as the complex cepstrum method, autocorrelation method, cycle diagram method, autoregressive model power spectrum method, and singular value decomposition method. Most of these methods are more complicated in calculations, and practical applications often require higher pulse frequencies and longer observation times, which are greatly restricted. In this paper, a classification method based on ensemble empirical mode decomposition and multifractal correlation (CMEEMDMFC) is proposed. The basic design idea is to obtain the intrinsic mode functions (IMFs) by using the signal decomposition ability of ensemble empirical mode decomposition (EEMD) and select some components which are beneficial for improving the signal-to-noise ratio (SNR) for recombination. Then extract the corresponding multifractal correlation (MFC) features from the new signals for recognition. For verifying the validity of the model, a comparison model was selected to test on the same data set. Experimental results show that the proposed model performs well in classification accuracy.

We studied electromagnetic wave propagation in a system that is periodic in both space and time, namely a discrete 2D transmission line (TL) with capacitors modulated in tandem externally. Kirchhoff's laws lead to an eigenvalue equation whose solutions yield a band structure (BS) for the circular frequency ω as function of the phase advances k_xa and k_ya in the plane of the TL. The surfaces ω(k_xa, k_ya) display exotic behavior like forbidden ω bands, forbidden k bands, both, or neither. Certain critical combinations of the modulation strength m_c and the modulation frequency Ω mark transitions from ω stopbands to forbidden k bands, corresponding to phase transitions from no propagation to propagation of waves. Such behavior is found invariably at the high symmetry X and M points of the spatial Brillouin zone (BZ) and at the boundary ω = (1/2)Ω of the temporal BZ. At such boundaries the ω(k_xa, k_ya) surfaces in neighboring BZs assume conical forms that just touch, resembling a South American toy ``diábolo''; the point of contact is thus called a ``diabolic point''. Our investigation reveals interesting interplay among geometry, critical points, and phase transitions.

Substrate integrated E-plane waveguide (SIEW) was invented recently to design E-plane waveguide devices on printed circuit board, which cannot be achieved by using the conventional substrate integrated waveguide (SIW). This paper is the first time to present an E-plane displaced SIEW junctions bandpass filter. The proposed design is shorter than the recently published SIEW septa filter and has a smaller footprint than several other SIW filters. It is designed by mapping an equivalent E-plane waveguide filter to its SIEW implementation. A filter prototype is built and measured for validation.

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.