This paper introduces a reconfigurable polarization MIMO (Multi-Input Multi-Output) dielectric resonator antenna at millimeter-wave frequency band. The proposed antenna consists of four single dielectric resonator antennas that are placed in 2×2 configuration to form a MIMO antenna, and also this design is based on using the pin diode switching concept to control the antenna polarization. In order to modify the antenna structure for different polarizations, two pin diodes are used in the ground place of the MIMO antenna. The designed antenna operates at 4.35 GHz for polarization diversity applications of the modern wireless MIMO systems. The proposed antenna covers a bandwidth of 11.26% at the central frequency and provides circular and linear polarizations with high gain around 6.4 dB. The antenna performance in terms of reflection coefficient, gain and axial ratio bandwidth in different modes (ON-ON, ON-OFF, OFF-ON and OFF-OFF) is measured. The advantages of the designed antenna are simple structure (using two pin diode switches to modify antenna polarization), high gain, low profile, and light weight. According to the measurement and simulation results, the designed antenna displays good return loss and radiation performance. Using the plexiglass as an antenna material which is very cheap and available in different dimensions is another advantage of the proposed antenna which reduce the fabrication cost.
To meet the requirements of miniaturization, multi-functions, and anti-interference of the antenna, this paper proposes a compact dual notch band frequency reconfigurable ultra-wideband (UWB) antenna. The antenna consists of an angle-cut rectangular radiation patch, a coplanar waveguide (CPW) structure, and a defective ground structure (DGS). A C-slot and an inverted U-slot are introduced to eliminate the interference of the Indian National Satellite band (INSAT), 5G band, and X satellite communication band. By controlling the PIN diodes across the two slots, the antenna can work in four states: UWB, two single notch bands, and one dual notch band. The impedance bandwidth in UWB mode is 2.9-12 GHz, with a relative bandwidth of 122%. The notch frequencies are 4.2-5.2 GHz and 6.2-8.1 GHz, respectively. In the passband of the antenna, the maximum gain is 7.17 dBi, and the group delay is less than 1 ns. The antenna size is 18 × 17 × 1.6 mm3, which is easy to integrate with the communication systems. The antenna can be freely switched between the UWB mode and each notch band mode, which can be applied to the UWB wireless communication systems.
Confining electromagnetic (e-m) modes in a tiny space is a desirable aspect for many applications including targeted material heating and light harvesting techniques. In this work, we report spatially squeezed e-m modes of a cavity resonator formed by the modified transformation optical (TO) medium. The proposed coordinate transformation scheme suggests curved contours of refractive index profile such that the e-m mode can be confined within the contours. The effective mode area for a TO cavity is at least 10 times smaller than the air-filled metallic cavity. The confined e-m modes of a proposed cavity are horizontally flattened but vertically squeezed of the dimension of λ/49. The material parameters of the proposed TO medium are approximated with non-magnetic and isotropic dielectric values. For an application aspect, squeezed mode of the TO cavity is used for targeted material heating, and it is demonstrated based on e-m thermal co-simulations. A tiny dielectric material placed at the squeezed part of the cavity mode is heated rapidly with the temperature rise of 2.350˚C/s (110˚C/s) for the single (dual) e-m source excitation with the peak electric field strength of 5 x 104 V/m. We further discuss how one can realize the proposed TO medium practically with a cell-grid approximation using photonic crystals and metamaterials.
An outer rotor coreless bearingless permanent magnet synchronous generator (ORC-BPMSG) has the characteristics of long service life, high efficiency, low noise, etc. However, the stability and reliability of the system and the output voltage are affected by the rotor vibration. In this paper, the step size and error of improved variable step least mean square (VSLMS) adaptive filter using improved simplified particle swarm optimization (ISPSO) is proposed, which suppresses the vibration of the rotor. The mathematical model and working principle of the ORC-BPMSG are introduced. The performances of improved VSLMS adaptive filter parameters are optimized by the improved SPSO algorithm, which generates a compensation signal to realize vibration compensation. The simulation system for the vibration compensation of the ORC-BPMSG is constructed, and dynamic suspension experiment and variable speed experiment of the rotor are carried out, which verify the robustness and stability of the proposed method.
A new approach to the bandwidth maximization of reconfigurable antenna arrays for monopulse radar applications is proposed and tested. The provided radiating systems allow switching the radiation behavior from sum to difference patterns (and vice versa) while sharing the excitation amplitudes of a user-decided set of radiating elements. Furthermore, the proposed design procedure guarantees the maximum possible bandwidth performance once the overall antenna size, the desired beamwidth, sidelobe level, and slope in the target direction of the generated power patterns are fixed. The synthesis problem is cast and solved as a sequence of convex programming optimizations, and hence the maximization of performances is attained with advantages in terms of computational times as well as convergence to the global optimum. The given theory is supported by numerical experiments including arrays with ultra-wideband performances.
A novel miniaturized bandpass filter (BPF) is proposed, which is based on a stepped-impedance resonator (SIR) and cross-coupling theory. This filter has the characteristics of small size and high out-of-band rejection. The filter consists of four 1/2 wavelength stepped-impedance resonators and two 1/4 wavelength short-circuit microstrip resonators. By designing a new kind of structure, the cross coupling is realized between the second and the fifth resonators, and two transmission zeros are introduced out of band. Zero-degree feeding is realized due to the symmetry of the structure and feeding position, which adds two other transmission zeros outside the band. Four transmission zeros are introduced outside the passband of the filter, which greatly increase the out-of-band rejection of the filter. The passband of the filter is 3.2 GHz~4.2 GHz, and the out-of-band rejection at 2.6 GHz and 4.8 GHz reaches -60 dB. The size of the filter is only 7.2 mm * 8 mm (0.21λg*0.24λg), which realizes the miniaturization of the filter.
In this paper, a potential-based partial-differential formulation, called the all-frequency stable formulation, is presented for the accurate and robust simulation of electromagnetic problems at all frequencies. Due to its stability from (near) dc to microwave frequencies, this formulation can be applied to simulate wide-band and multiscale problems without encountering the infamous low-frequency breakdown issue or applying basis function decompositions such as the tree-cotree splitting technique. To provide both efficient and flexible numerical solutions to the electromagnetic formulation, a mixed continuous-discontinuous Galerkin (CDG) method is proposed and implemented. In regions with homogeneous media, the continuous Galerkin method is employed to avoid the introduction of duplicated degrees of freedom (DoFs) on the elemental interfaces, while on the interfaces of two different media, the discontinuous Galerkin method is applied to permit the jump of the normal components of the electromagnetic fields. Numerical examples are provided to validate and demonstrate the proposed numerical solver for problems in a wide electromagnetic spectrum.
Doppler-based techniques for ocean current measurement have been demonstrated in the past years. The Doppler shift of the ocean backscattering from space-borne microwave instruments not only includes the contributions from ocean current but also includes satellite movement and the wind-wave induced. Geometrical Doppler shift induced by satellite movement is highly dependent on the accuracies of satellite attitude determinations and speed. In this study, we derive the detailed formulas to investigate how satellite attitude determination and speed errors affect ocean current retrieval for a Doppler scatterometer through the spatial correlation coefficient phase and the transformation between orbital coordinate system and satellite-carried local level frame (LLF). Our results show that ocean current speed retrieval accuracy is sensitive to the accuracies of satellite attitude determination and speed, and compared with the satellite speed error, satellite attitude error has a larger impact on ocean current retrieval. By comparisons, with the same attitude accuracy for satellite roll, pitch, and yaw, ocean current speed error induced by the roll error is found to be the smallest. With an accuracy of 0.001° satellite attitude determination and 0.01 m/s for satellite speed accuracy, the total ocean current speed retrieval error induced by satellite attitude determinations (including roll, pitch, and yaw) and speed errors reaches a maximum value of 16.37 cm/s at side-looking direction and a minimum value of 11.05 cm/s at forward and backward-looking directions. Our results confirm the importance of satellite attitude determination accuracy for future ocean current mission and will also be useful to motivate the design of future Doppler measurement instruments.
The aim of this paper is to develop a hybrid modeling approach based on direct coupling between the finite element method (FEM) and the partial element equivalent circuits method (PEEC). Through this FEM-PEEC approach, we can efficiently compute the three-dimensional eddy current distribution created by a rectangular coil (exciting coil) in conductive and magnetic structures having heterogeneous dimensions. Magnetic field created by the rectangular coil is given by calculating quasi-static Green's function integrals. In goal to construct rectangular coil, the calculation is made for elementary parallelepipedic conductors oriented respectively in x and y directions. By this manner, three possible configurations are proposed and compared to show errors, especially in corners. By only meshing the active parts of the domain (without air region), we confirm through the issued results that the proposed methodology contributes to accelerate the execution time while maintaining the precision. The obtained results are validated with the numerical ones by 3D FEM (Flux 3D Software).
The experimental validation of reduced grating lobes in a seven-element, hexagonal, scanning phased array antenna with the one-wavelength element spacing is presented. The base element of the array is a single-layer, dual-mode antenna with self-scanning and nulling properties. For the selected scan angle of -30°, the required microstrip transmission line based feeding network, consisting of ring hybrids, power splitters, and branchline couplers, are designed and developed. A prototype of the complete array and feeding network was fabricated and successfully tested to show the effectiveness of the grating lobe reduction method using the dual-mode antenna elements in scanning phased array antennas with the one-wavelength element spacing.
In order to satisfy the requirements of 2G/3G/4G wireless communication, two kinds of base station antennas with wideband, dual-polarized and three-modes are proposed in this paper. Firstly, a pair of diamond dipoles is placed in an orthogonal way to realize dual-polarizations, then a pair of Y-shaped branches is added to generate a new mode. The Y-type coupling feeding can increase the impedance bandwidth without increasing the size of antenna. The antenna achieves an impedance bandwidth of 51.75% (1.69-2.87 GHz) with a return loss lower than -14 dB. The antenna also has a stable radiation performance. The gain is greater than 8.6 dBi, and the port isolation is less than -27 dB over the entire frequency band. Then based on above antenna, a C-type slot notched antenna is added to improve anti-interference ability. Finally, band stop characteristics are obtained by etching a C-type slot line resonator on two dipoles. The results show that the bandwidth is 1.7-2.69 GHz, and the sharp notched band is 1.8-1.95 GHz. The C-type slot line here can be regarded as a quarter wavelength resonator in series. Moreover, the isolation of the port is less than -28 dB, and the 3 dB beamwidth in the bandwidth is 66±5˚. Both antennas are fabricated and have dual polarizations, simple structure, and good radiation performance, which can be used in the next generation of wireless communication.
Transverse electromagnetic (TEM) cell is usually used to evaluate the electromagnetic immunity and electromagnetic radiation disturbance of the equipment under test (EUT) and integrated circuit (IC). Affected by the structure of the TEM cell, high-order modes and reflection will be generated in the high frequency range, which will limit the higher frequency applications of the TEM cell. In this paper, the TEM cell specified in IEC61967-2 standard is improved by adopting several methods, including segmented impedance matching, slitting outer conductor, slotting inner conductor, adding absorbing materials and adding an external shielding box. The results show that the improved TEM cell voltage standing wave ratio (VSWR) is less than 1.2 in 0-3.4 GHz, less than 1.3 in 0-3.75 GHz, and less than 1.5 in 0-4.06 GHz; at the same time, the S-parameter characteristics are better.
In this paper, the bandwidth of a bowtie antenna is improved to meet the requirements of Ground Penetrating Radar (GPR) applications that need a fractional bandwidth greater than 100% and are able to operate at low frequencies. This was done using several modification steps, which were the use of Antipodal technique for its advantages in reducing the complexity of the feeder network to achieve good matching with a standard 50-Ω SMA connector, bending the four corners of the arms and adding a triangular slot in each arm. The simulation was carried out using CST Microwave Studio to study the effect of each modification step on improving the bandwidth. The simulation results of the new antenna achieved a fractional bandwidth of 138% within the frequency range (1-5.45) GHz at the values of return loss (S11≤-10 dB). The new antenna was also fabricated, and the return loss was measured and showed a good agreement with the simulation results.
Pneumothorax can cause chest tightness, chest pain, and respiratory failure, which can be life-threatening in severe cases. Therefore, early diagnosis and treatment of pneumothorax are crucial. Magneto-Acousto-Electrical Tomography (MAET)is an imaging technique in which ultrasound and electromagnetism are mutually coupled. It has the advantages of high spatial resolution and high image contrast. In this paper, we use MAET to study porous and air-containing lung tissue. We first simulate the characteristics of the MAET signal as the degree of pneumothorax increases. The relationship between the size of the ultrasonic probe and the size of the pneumothorax was discussed. The simulation results show that the reflection and attenuation values of the MAET voltage signals increase as the pneumothorax size gradually increases, regardless of whether the ultrasound transducer size is larger or smaller than the pneumothorax size. Finally, the MAET experimental platform was built to validate the simulation results of MAET signals. The results of the experiment and simulation are consistent with each other. The research of this paper has a certain reference value for the detection of pneumothorax using MAET.
This work discusses the effect of reconfigurability on a Sierpinski-carpet fractal microstrip patch antenna. The implementation of reconfigurability is achieved by modeling a PIN diode as a lumped RC element on HFSS (High Frequency Structure Simulator) simulation tool. The proposed antenna design is also fabricated and tested. It is highly miniaturized having a dimension of 9.5 mm × 7.4 mm and a significantly high impedance bandwidth which is desirable for most wireless communication applications. The resultant Fractal Reconfigurable Antenna (FRA) exhibits good performance parameters having frequency reconfigurability rendering it useful for Ku/K/Ka band applications.
In this paper, a single-feed cylindrical dielectric resonator antenna (DRA) with wide angular circular polarization is proposed. It is composed of a cylindrical cavity loaded cylindrical dielectric resonator (DR), an orthogonal slot with curved arms, and an off-centered L-shaped microstrip line. By inserting the slot with curved arms and a cylindrical cavity, the 3-dB axial ratio beamwidth (ARBW) can be increased, and symmetric radiation can be obtained. For validation, a prototype is designed at 1.7 GHz and fabricated. The overall size is 0.39λ0 × 0.39λ0 × 0.13λ0. The measured results show that it exhibits a 10-dB impedance bandwidth of 33.3% (1.45~2.03 GHz) with a circularly polarized (CP) bandwidth of 16.1% (1.54~1.81 GHz). Symmetric radiations are obtained, and the 3-dB ARBWs in the xoz and yoz planes are more than 150° over the CP bandwidth.
In this paper, a novel circularly polarized rectenna, with a harmonic suppression, capable of harvesting low-power RF energy with wide operating output loads is presented. The proposed rectenna is composed of a circularly polarized CPW-fed antenna based on a split ring resonator (SRR) and a wideband rectifying circuit. The circular polarization characteristic is achieved by breaking the symmetry of the SRR. The designed topology is fabricated and measured. Simulated and measured results show that the rectenna's efficiency is more than 45% at 2.45 GHz with an input power of -15 dBm under different polarizations. Importantly, the measured results show that the proposed configuration can maintain the same efficiency over wide ranges of loads (from 1 to 5 kΩ). The measured output dc voltage of the rectifier with a load resistance of 3-kΩ is 0.21 V and 1.22 V at -15 dBm and 0 dBm, respectively. The proposed design concept is very suitable for the 2.45 GHz ISM band (Wi-Fi, Bluetooth, RFID, etc.).
Seawater is generally considered as an electrical conductor with rather weak electrical conductivity. As a moving electrical conductor in an electromagnetic field, seawater motions induce weak electromagnetic field in surrounding environment. The movement of vessels in seawater leads to the variations of electromagnetic field pattern, called as magnetic wake. In order to detect a moving object through the induced magnetic wake, a magnetometer can be placed under the seawater surface. In this paper, we present a mathematical model through which we can study the magnetic wake in water of finite depth and, explore its behavior with respect to environmental parameters and geometric characteristics of the moving object. More specifically, we show through mathematical expressions and numerical results that there always exists an optimal depth under the sea surface wherein if amagnetometer isplaced, maximum amplitude of magnetic wake can be captured. Several key properties are verified for the optimal magnetic wake detection through numerical results. Firstly, the optimal depth is increased by increasing the speed of the moving vessel. Secondly, the optimal depth is not influenced considerably by the variation of sea depth, and thirdly, in the case wherethe Froude number of the vessel is lower than 0.5, the optimal depth is below 15 m.
The magnetic-geared generator integrates the magnetic gear and the generator by using the magnetic field modulation technology. It has the characteristics of high power density, high material utilization, and has a wide application prospect. However, compared with the general generator, its structure is relatively complex which makes its design and optimization become more complex. Therefore, a new structure and an optimization method based on orthogonal regression statistics is proposed. The experimental results fully prove the effectiveness of the proposed structure and optimization method.
In this paper, half-mode substrate integrated waveguide (HMSIW) bandpass filters with modified complementary split-ring resonators (CSRRs) for the reduction of machining tolerance sensitivity are presented. Profiting from the evanescent-mode resonance operation, the conventional CSRR and its modified versions have been successfully utilized to miniaturize the physical sizes of SIW components. However, few investigations have focused on the fabrication tolerance. Performance of most CSRR-loaded SIW components, as well as their modified versions, is significantly sensitive to the fabrication tolerance. Hence, as the conventional machining process is with large fabrication tolerance, the CSRR-loaded SIW components suffer from limited performance and restrained application practicability. To decrease the influence from the machining tolerance on the components' performance, the slots-embedded CSRR (SECSRR) is proposed and loaded into HMSIW to design evanescent-mode filters. Numerical simulations exhibit that the proposed SECSRR can help to decrease the machining tolerance sensitivity effectively as the fractional frequency offset resulting from the fabrication error is reduced from ±8.11% to ±4.95%, which indicates that the proposed SECSRR is able to improve the suitability of SIW/HMSIW components and circuits for practical radio frequency (RF) and microwave applications.