In this paper, the performance of a concentric hexagonal antenna array (CHAA) is investigated with the exploitation of a robust variable diagonal loading (VDL) technique in the presence of direction of arrival (DOA) mismatch. The performance of minimum variance distortionless response (MVDR) based CHAA is compared with the performance of existing MVDR based concentric circular antenna arrays (CCAAs), and it is found that the proposed MVDR based CHAA provides 25.54% narrow half-power beamwidth (HPBW) and lower side lobe level than the existing MVDR based CCAAs. When DOA mismatch occurs between main beam steering direction and actual signal-of-interest (SOI) direction, the performance of MVDR based CHAA is deteriorated. In the case of DOA mismatch, to ameliorate the performance of CHAA, this paper proposes VDL technique for the CHAA processor and compare the performance of proposed robust CHAA with existing robust CHAAs. The proposed VDL based robust CHAA delivers 88.37% and 78.56% higher output power for 2˚ DOA mismatch than existing fixed diagonal loading (FDL) and optimal diagonal loading (ODL) based CHAAs, respectively. Several tapering window functions are proposed to reduce the side lobe level of CHAA. Performance of the proposed beamformer is analyzed utilizing MATLAB environment in various scenarios.
A new wideband dual-polarized patch antenna using substrate-integrated waveguide (SIW) technology is proposed in this paper. The antenna is composed of a patch radiator and a square SIW cavity. The square patch is internally embedded in the square SIW cavity with a surrounded slot. A pair of L-shaped probes are used for the excitation of the orthogonal linearly-polarized signals. The dominant resonant mode of the square patch resonator (TM010) and the modes of the SIW cavity (TE110 and TE120/TE210) are employed to achieve a wide impedance bandwidth under these resonances. By introducing two shorting pins, the isolation between two feeding ports can be enhanced to more than 21 dB. The resonant properties of these modes are investigated based on the cavity model theory. Then, their resonant frequencies are discussed to provide information for designing and optimizing such an antenna. For demonstration, a prototype is fabricated and measured. The measured results show that the proposed antenna achieves a wide impedance bandwidth of about 66.7% (3.71-7.43 GHz) and 70.9% (3.58-7.52 GHz) for horizontal and vertical polarizations, respectively. A stable gain in the range of 7.15 to 8.03 dBi is obtained within the operating band. Due to the SIW cavity-backed structure, the antenna shows unidirectional radiation patterns and low back-lobe radiation at the resonant frequencies. Thus, the antenna is highly suitable for the base station antenna that is required to cover the bandwidth of 5.5 GHz WiMAX and 5.2/5.8 GHz WLAN systems.
A wideband high gain three-layer hemispherical dielectric resonator antenna (HDRA) that operates at TE511 and TE711 higher order modes is proposed. The HDRA is composed of three layers, which has permittivities of 20, 10 and 3.5. The multilayer structure has been chosen in order to reduce the Q-factor and achieve a wider impedance bandwidth. Cross slot feeding mechanism has been utilized taking into account the excited higher order modes for gain enhancement. The proposed antenna provides an impedance bandwidth of 35.8% over a frequency range of 20.8 to 29.9 GHz in conjunction with a high gain of ~9.5 dBi. The proposed DRA represents the first attempt in utilizing a mm-wave hemispherical DRA.
When a high voltage direct current (HVDC) system works at single line operation mode, a big current will flow into the earth through the grounding system directly. Then the large current can cause damage to surrounding equipment and the environment. Therefore, it is significant to study the current dispersion characteristics of HVDC grounding system. Firstly, a ±800 kV HVDC model operated at single line mode is built. The grounding current can be seen as the equivalent current source injecting to the grounding system. Secondly, the current dispersion characteristics of horizontal, cross and ring electrodes are investigated. It proves that the ring grounding electrode shows better current dispersion characteristic. And the double-ring grounding electrode whose ratio of inner and outer rings is controlled at 0.7 to 0.75 can get a better current dispersion characteristic. In addition, a dynamic seasonal frozen soil resistivity changing model is built to study the effects of season on the grounding electrodes. The frozen soil would not only increase the ESP, the resistance to ground, and step voltage, but also reduce the current density and electrical field. When the frozen soil is melting, the current dispersion characteristics are the best. The results provide meaningful reference for the design of the grounding system in extremely cold regions.
The aim of this research is to propose a new efficient and reliable approach on the field of Non Destructive Testing (NDT), for the characterization of cracks in non-ferromagnetic material by Electromagnetic Acoustic Transducer (EMAT). EMAT is an ultrasonic technique that generates and detects ultrasonic waves in the conductive material without physical contact. The research goes through two principal phases. The first, which is a forward model, is based on Finite Element Method (FEM). The FEM is applied to simulate the EMAT response (output voltage) to the material under test in order to build a database for the inversion tool. The second is the inverse model and depends on the Partial Least Square Regression (PLSR) method, as it is a fast, simple, and accurate inversion tool, in order to estimate the depth and width of the cracks on the surface of non-ferromagnetic materials. PLSR is a dimensionality reduction method which aims to model the relationship between the matrix of independent variables (predictors) (X) and the matrix of dependent variables (response) (Y). The purpose of PLSR is to find the Latent Variables (LV) that have a higher ability of prediction by projecting original predictors into a new space of reduced dimensions.
In this work, the design of an ultra-wideband (UWB) fork monopole antenna based on a surface impedance substrate integrated waveguide (SIW) resonator has been proposed. The SIW resonator not only improves the antenna bandwidth and its performances, but also permits to reduce the antenna size and weight. An antenna prototype has been designed, fabricated, and experimentally assessed. The obtained results are quite satisfactory, and they demonstrate the potentialities of the proposed geometry.
In this paper, an S band, 300 MHz bandwidth, and 20 kW average power klystron was developed in the Aerospace Information Research Institute, Chinese Academy of Sciences. The klystron operates at 72 kV beam voltage and 41 A beam current with peak powers of over 850 kW and efficiency of over 30% at a 2.47% RF duty cycle. The results, including simulations, design, technologies and performances of the klystron, are presented. Some problems, such as gain dip, high order mode oscillation, output window cracking, and startup time, were also discussed.
In this paper, an absorptive filter-integrated switch (FIS) using switchable T-shape resonators is presented. The FIS was made up of two absorptive T-shape resonators and integrated with single pole double throw (SPDT) switch. A simple mathematical analysis of isolation and insertion loss of filter-integrated SPDT switch is discussed. PIN diodes were used as the switching elements for the SPDT switch and to reconfigure between the band-stop and bandpass responses. The proposed absorptive FIS design could be used for internet of things (IoT) applications such as Zigbee and Bluetooth at an operation frequency of 2.45 GHz. As a result, the proposed FIS exhibited low magnitude of insertion loss and high isolation. Therefore, the key advantages of the proposed FIS design are low insertion loss, high isolation, and good return loss at both ON- and OFF-state ports.
In electronic beam scanning, the number of phase shifters is an obvious challenge. So, there are several methods to reduce the number of phase shifters. The aim of this paper is to investigate the use of the meta-heuristic algorithm to lower the grating lobe level in the subarray antenna. Improve the result obtained by group subarray optimization techniques to determine topology and space between elements, and complex optimization of weight, simultaneously. Uniform subarray and random subarray are analyzed in Matlab to determine the coefficient of excitation by the evolutionary algorithm, as well as swarm and hybrid. The results of the simulation are shown; this method leads to radiation pattern without grating lobe in wide scanning angle. It indicates that there is a possibility of obtaining wide electronic scanning with minimum number of phase shifters and improving result.
Petri net is a mathematical and graphical tool used for analyzing the properties of parallel and concurrent system designs. Here, it is used for checking the process modeling of 4 × 4 Butler matrix fabricated on Rogers RO3210 and resonating in Ku band. Butler matrix is well suited for satellite and aircraft antenna applications as a feeding network for phase array systems. So, this basic feed design process of antennas is studied using Petri nets for better understating the designing process and removal of any deadlocks occurring during designing and feeding of antennas. It is accomplished by analyzing the behavioral and structural properties of Petri nets. A Butler matrix divides the power amplitude into four equal parts and provides a progressive phase difference of 45˚. Therefore, its components, 0 db coupler, 3 db coupler, and phase shifters, have also been designed and simulated. After designing the components, firstly these components are joined to form a matrix design which is simulated and fabricated in ANSYS HFSS. Secondly, the designed structure is analyzed for structural and behavioral properties using Petri net's graphical and mathematical properties. After analyzing the process, the feed design can be modified further according to user requirements, and deadlock can be removed by checking the difference between the simulated and measured results of design. Likewise, here the matrix has been compared and found to be following the same pattern. The overall size of the matrix is 5.58 × 7.43 cm2, which is further suitable for the user's feeding requirements and applications.
This paper presents new ways of modelling several types of faults that can be encountered while monitoring cables throughout their lifecycle. These models comply with the traditional RLGC representation of a transmission line, which makes them easily usable for numerical simulations in frequency-domain. Theoretical fault signatures will then be extracted in Y. J., J. Powers, T. S. Choe, C. Y. Hong, Etime-domain to provide a better way of analyzing plots given by traditional devices, like time domain reflectometers (TDR). This allows a more accurate assessment of a cable's health and condition. It will be shown in particular that some faults can be detected even if their damaged zone remains small compared to the wavelength. A direct benefit from this is that very expensive high frequency tools are not always necessary to detect these faults. The general objective of this paper is to improve fault location accuracy by combining measurement and simulation. It will be shown how this combination can become a powerful tool to detect, locate and characterize a defect in a cable. The suggested models can be applied to any type of cable, from a coaxial line to a multi wire harness. In this work, a focus has been put on civil and military aircrafts, but similar cables are also found in cars or nuclear power plants for instance.
A differentially compact dual circularly polarized (CP) concentric ring traveling wave-fed quasi-lumped resonator (QLR) array working at 5.8 GHz is presented. The array consists of seven series QLRs, each with an interdigital finger capacitor, connected by a parallel narrow-strip inductor. The CP was obtained by organizing the radiating QLR over a concentric ring-fed microstrip. The QLR was fed with a current of the same magnitude and some phase delay at each element. The dual-port feeding permitted the selection of the traveling wave direction and, consequently, the mode of CP. The measured bandwidth was 5.76-5.8 GHz at port 1. Meanwhile, the bandwidth was 5.75-5.77 GHz at port 2. The measured peak gain was 5.9 dBi at port 1 and 6.4 dBi at port 2. The cross-polarization was 19 dB lower than the co-polarization at port 1, which is a characteristic of right-hand circular polarization (RHCP). The cross-polarization was 14 dB higher than the co-polarization at port 2, which is a characteristic of left-hand circular polarization (LHCP). The size of each radiating element was 5.8 × 5.6 mm2, and the array was 40 × 40 mm2. These features and its compact size make the proposed array antenna a good candidate to be used in wireless systems.
In this paper, a novel OLR loaded self complementary dipole antenna (OSCDA) is proposed. Open loop resonators (OLRs) are introduced into the design of a traditional self complementary dipole antenna (SCDA), to evolve it into OSCDA. The antenna is compact and has an impedance bandwidth of 1.1 GHz to 3.3 GHz with VSWR less than 2 across the frequency band. The use of the proposed antenna as a liquid sensor to detect adulteration in liquids is demonstrated from the relationship between concentration and shift in resonant frequency and variation in reflection coefficient. Variation of reflection coefficient due to change in dielectric properties is studied for different cases viz.: (i) dilution of milk with water, (ii) adulteration of coconut oil with rice bran oil, (iii) adulteration of honey with sugar syrup, and (iv) varying concentration of salt and sugar in water. When an adulterant is added to a liquid or concentration of solute in a solution varied, the dielectric properties change. This is reflected in the variation in reflection coefficient and resonant frequency. Experimental results show that the antenna has a good sensitivity to detect adulterated samples.
Exact two-dimensional (2D) analytic expressions for electric and magnetic fields and their potentials created by a linear beam of relativistic charged particles between infinite perfectly conductive plates and ferromagnetic poles are derived. The solutions are obtained by summing an infinite sequence of fields from linear charge-images and current-images in complex space. Knowledge of the normal component of the electric field on the conductor surface makes it possible to calculate the induced electric charge surface density. In addition, we derive within an improved linear approximation new analytical expressions for fields near the beam in the case of an arbitrary beam offset from the median plane. The mathematical features of exact solutions and limitations for the applicability of linear approximations are specified. The primary goals of the future high-luminosity p-p and heavy-ion Large Hadron Collider programme after the Long Shutdown 2 are the search for yet unobserved effects of physics beyond the Standard Model, searches for rare or low-sensitivity processes in the Higgs sector, and probing in more detail the mechanism of electroweak symmetry breaking. This programme relies on the stable operation of the accelerator. However, as the beam luminosity increases, a number of destabilizing phenomena occur, in particular field emission, enhancing the electron cloud effect. For the case of a proton beam, we apply the exact 2D solution for estimating the intensity of electron field emission activated by the electric field of the beam in collimators of the future high-luminosity Large Hadron Collider. Calculation shows that the field emission intensity is very sensitive to a collimator surface roughness. In addition, with a relatively small and accidental beam displacement from the median path, about 20% of the collimator half-gap, the emission intensity increases by a factor of 107. This will partially neutralize the beam space charge, violating acceleration dynamics and enhancing instability effects.
This paper proposes a new method to enhance the impedance bandwidth (IBW), broadside gain, front-to-back ratio, and aperture efficiency of a rectangular microstrip patch antenna (RMPA) printed on a compact artificial magnetic conductor ground plane (AMC-GND). The technique uses large shorted unit cells at the center and a wide slot cut on the unit cells located under the patch to respectively impede the propagation of surface currents and reduce the adverse effect of the loading capacitance that is formed between the RMPA and the AMC-GND on the antenna IBW. The proposed antenna with dimensions of only 1λ0×0.6λ0×0.06λ0, realizes an IBW of 24% (6.07-7.73 GHz), peak gain of 9.93 dBi, and a simulated aperture efficiency of more than 96%. Due to its compact size, good radiation, and wide IBW performances, the presented antenna can be used in various applications, such as MIMO antenna system, wide-angle scanning antenna array and reflector feed antennas operating in satellite C-band 5.9-6.4 GHz and 6.425-6.75 GHz. It is worth mentioning that the main contribution of the current work is the investigation of the detrimental effects of the overlay capacitor on the IBW of a linearly polarized RMPA etched on a compact AMC surface using a simple equivalent circuit model.
In this paper, a novel microstrip-fed compact antenna with dual band-notched characteristic is presented for ultra-wideband (UWB) applications. Assisted with symmetrical open-circuited stubs, a UWB impedance matching can be achieved. A novel modified capacitively loaded loop (CLL) resonator is proposed to realize the dual notched bands. By symmetrically placing a couple of proposed resonators in the vicinity of the feed line, dual band-notched properties in 3.4-3.7 GHz for WiMAX and 5.15-5.825 GHz for WLAN are generated. The good performance of the dual notched bands, stable gain, and radiation patterns in the operating bands make the proposed antenna a good candidate for various UWB applications.
A compact tri-band antenna is designed and analyzed to achieve both transmission and reception of direct broadcast service (DBS) and fixed satellite service (FSS) in Ku band. The proposed antenna design consists of a truncated E-shaped slot, eight rectangular slots, two C-shaped slots in the patch and eight defected ground structure (DGS) slots. The three frequency bands of 11.40-12.91 GHz, 13.86-14.53 GHz, and 17.20-17.86 GHz are achieved with impedance bandwidths of 12.32%, 4.73%, and 3.77% respectively. Conversely, the measured frequency bands of 11.40-12.98 GHz, 14.21-14.86 GHz, and 17.41-18.98 GHz with the impedance bandwidth of 12.70%, 4.48%, and 8.63% respectively are obtained. The simulated results of the proposed antenna are compared with the results of fabricated antenna and are found to be satisfactory for reflection coefficient, impedance bandwidth, polarization, efficiency, gain, and radiation pattern. Moreover, the proposed antenna design can be used as an element in an array configuration to achieve high gain in both transmission and reception modes of FSS and DBS.
In this work a reconfigurable Ultra Wide Band (UWB) antenna for Wireless Body Area Network (WBAN) is presented. The antenna is completely composed of fabric materials and is able to switch its topology from a monopole-like structure (for on-body communications) to a microstrip-like structure (for off-body communications) maintaining UWB characteristic stable both on body and in free-space. This antenna presents good radiation properties in both configurations. In order to describe its time domain and frequency domain behavior a System Fidelity Factor (SFF) analysis has been done for both topologies.
Time domain finite element methods (TD-FEM) for computing electromagnetic fields are well studied. TD-FEM solution is typically effected using Newmark-Beta methods. One of the challenges of TD-FEM is the presence of a DC null-space that grows with time. This can be overcome by solving Maxwell equations directly. One approach, called time domain mixed finite element method (TD-MFEM), discretizes Maxwell's equations using appropriate spatial basis sets and leapfrog time stepping. Typically, the basis functions used to discretize field quantities have been low order. It is conditionally stable, and there is a strong link between time step size and mesh dependent eigenvalues, much like the Courant-Friedrichs-Lewy (CFL) condition. This implies that the time step sizes can be very small. To overcome this challenge, we use the Newmark-Beta approach. The principal contribution of this work is the development of, and rigorous proof of, unconditional stability for higher order TD-MFEM for different boundary conditions. Further, we analyze nullspaces of the resulting system, and demonstrate stability and convergence. All results are compared against the conditionally stable leapfrog approach.
The problem of radiation of a magnetic dipole axially symmetric with an infinitesimally thin perfectly conducting circular disk is solved in an exact closed form. This is done by transforming the original dual integral equation system describing the problem into a single second-kind Fredholm integral equation and searching for the solution as a power series. Both low- and high-frequency asymptotic limits are also discussed from which simple approximate solutions are readily derived. Numerical results are provided to validate the proposed formulation.