A comprehensive overview of dielectric resonator antenna (DRA) is presented in this paper. Several techniques have been reported in the literature for the performance improvement of DRA. Over the past few decades, circularly polarized (CP) DRAs have been widely explored to mitigate multipath fading and polarization losses in comparison to linearly polarized (LP) antennas. Apart from this, high data transfer rate is required, which needs the development in the field of multi-input-multi-output (MIMO) antenna designs. This includes the increase in the channel capacity without exploiting the limited constraints like signal power and bandwidth. Thus, exploring the concept of MIMO in DRA along with the diversity performance features leads to the development in this field. Furthermore, to mitigate the conduction losses at THz and optical frequencies, high-efficiency DRA proves rationale in extending towards the higher frequency ranges. These scintillating features pave the path for efficient devices integration and on-chip applications at higher frequency ranges where the performance of metallic radiator degrades. Also, the dispersive properties of metal conductivity lead to plasmonic behaviour resulting in the dissipation losses at the optical frequencies. These losses can be substantially mitigated using DRAs. This can be efficiently realized for the future application that requires the manipulation of high-resolution light.
The systematic design approach of a 42 GHz CW gyrotron has been extensively presented in this paper. Beam-wave interaction of the conventional tapered cylindrical cavity gyrotron is demonstrated using commercially available Particle-In-Cell (PIC) code. Beam absent and beam present cases have been considered to observe the performance of the device. Beam absent case is presented to validate the design in desired mode as well as resonant frequency whereas beam present case is demonstrated to validate and observe the beam-wave interaction behavior of the device in terms of output power. In order to optimize the dimension of interaction structure to achieve desired performance of the device, several parameters were considered. RF output power of the device is estimated with the variation of structure parameters as well as electron beam parameters to achieve better performance in terms of efficiency. Using the designed parameters, beam present analysis offers a saturated output power well above 250 kW. The particles phase space behavior along the interaction length is demonstrated to realize the energy transfer phenomena. The PIC simulation results are found in close agreement with the self-consistent single mode results. The estimated output power and efficiency support the proper design of proposed gyrotron oscillator.
A very economical and compact size wearable antenna operating over Ultra-Wide Band (UWB) spectrum is investigated in the proposed work. The antenna is modelled on a thin FR-4 (0.2 mm) material that makes it flexible and well-suited for wearable appliances. The radiating patch structure is the combination of one square and two elliptical patches rotated at 45˚ and fed with a Coplanar Waveguide (CPW) to achieve a wide impedance bandwidth. The complete radiating structure looks like a flower shape, and it has a partial ground to support the radiation from the antenna over the complete UWB. The flexibility of the proposed structure is investigated by bending it along xz and yz planes using cylindrical shape foam. The peak Specific Absorption Rate (SAR) is demonstrated for 1 g and 10 g of tissues at different chosen frequencies like 3.7, 8.4, and 11.2 GHz using a three-layer phantom model. The presented antenna performance analysis and compact size confirm that it is a good candidate for wearable applications.
This paper presents an analytical method for the optimal estimation of time constants of synchronous machine from Standstill Frequency Response Testing (SSFR). We show that the analytical method is advantageous over the conventional one since the latter is based on curve fitting representing the variation of the operational inductance as a function of the frequency and provides in accurate and non-unique solutions. In fact, the analytical method applies the standard theory of linear systems to locate the values of poles and zeros in the frequency response and determines the optimal order of the equivalent circuit that can model the machine accurately. The proposed method is simple, practicable and effective. However, it needs an optimisation process based on parameter differentiation, to improve the values of time constants. Based on the measured data, realistic tests are given to show the advantages of the method.
Compact wireless devices have been proposed as a result of the introduction of wireless communication systems, allowing more space to be used for other electronic components. A reconfigurable antenna is critical in today's cutting-edge wireless technologies. Reconfigurable antennas can perform a variety of tasks depending on their operating frequency, radiation pattern and polarization. Dynamic tuning can be done by altering mechanical, electrical, physical, or optical switches to run a certain switching mechanism. This can be accomplished using a single reconfigurable antenna that allows the user to customize a range of performance attributes such as resonant frequency, polarization and radiation pattern to meet their specific requirements. This paper looks into different types of reconfigurable antenna switching mechanisms, different types of effective implementation techniques, different types of reconfigurable antennas, and some recently proposed reconfigurable antenna designs for the Fifth Generation (5G) and IoT applications in various wireless communication systems.
Evaluation of the lightning coupling on the buried signaling cable nearby when the through-ground wire is used as the discharge channel of lightning current requires accurate models for the calculation of the underground lightning electromagnetic field and the induced current of this field on the signaling cable conductor. To accomplish this, a full-wave approach based on the finite-element method (FEM) is used, which incorporates the frequency dependence of soil conductivity and relative permittivity into in the model. The numerical results show that for soils characterized by relatively low resistivity values (less than 4000 Ω.m), the frequency dependence of the electrical properties of the soil has a negligible influence on the horizontal component of the electric field and the vertical component of the magnetic field. However, the distribution of the lightning electromagnetic field is markedly affected by the distance between the air-soil interface and the buried signaling cable. We also find that the coupling strength of the lightning electromagnetic field to the buried signaling cable is strongly dependent on the wave shape of the lightning current, soil resistivity, the distance between the cable and the air-soil interface, and the distance between the cable and the lightning strike point. Finally, the common grounding methods of the cable shielding layer in cable protection are compared. Results show that single-layer double-terminal grounding is the most effective anti-interference measure for the electromagnetic field coupling between the through-ground wire and the buried signal cable near the lightning point of the high-speed railway. The desired shielding effect properties with the frequency from dc to 1 MHz can be achieved using this method.
A novel polynomial-chaos (PC) techninullque is implemented based on anisotropic index sets. The proposed scheme takes advantage of the effect of each random variable on the output parameter of interest and adaptively constructs the PC expansion. Particularly, the algorithm starts by generating bases via low and high reliability heuristics and builds a PC representation, until an error criterion is satisfied or until the maximum desired polynomial order is reached. Our method is tested on a variety of uncertainty problems, where the statistical moments of the outputs of interest are estimated. Numerical results prove the efficiency of the proposed approach, since accurate outcomes are obtained in lower computational times than other techniques.
A novel signal processing scheme for identification of jet fighter targets by the onboard radar of active and hybrid homing missiles is proposed in the present work. For a specific target, the frequencies of the internal resonances of the cavity-backed apertures existing as the air-inlet pipes of the jet engine are used to construct an interior signature function for the proposed target identification scheme. For the purpose of quantitative description and assessment of the proposed scheme, electromagnetic simulation is used where the air-inlet pipe is modeled as an open-ended conducting cylinder with a number of radial conducting blades placed inside the cylindrical cavity near the open end. The transmitted radar pulse is formed by frequency chirping using linear frequency modulation (LFM) to include the frequencies in the band 1.0--2.0\,GHz with high sweep resolution. The selected frequency band is wide enough to distinguish among various jet fighter targets. The CST® simulator is used to evaluate the radar cross section (RCS) of the open-ended pipe model with the internal blades due to an incident chirped pulsed plane wave as mentioned above over the frequency band 1.0-2.0 GHz. The proposed target identification algorithm is mathematically described and computationally applied to identify different targets with different dimensions of the jet engine pipe. The effect of the additive white Gaussian noise (AWGN) on the correctness of the target identification decision using the proposed scheme is investigated by calculating the false alarm rate (FAR) with varying the signal-to-noise ratio (SNR). The numerical examinations show that the proposed algorithm succeeds in taking the correct decision regarding the target identification with FAR<10% for SNR} ≥ 12 dB.
This paper presents a CPW-fed, UWB-extended bandwidth, dual band-notched on-chip antenna with its equivalent circuit model. The UWB-extended bandwidth is realized by truncating the bottom corners of a rectangular patch radiator while a 90º-rotated `C'-shaped slot in the patch and a `U'-shaped slot in the feedline are used to achieve two notch bands for mitigating the signal interference in the frequency bands of 5.15 to 5.925 GHz and 7.9 to 8.8 GHz. Based on the fundamental theory, different parasitic as well as distributed circuit parameters associated with the designed on-chip antenna are extracted, and then the corresponding equivalent circuit model is configured from them. The resultant circuit is validated with the well approved full-wave electromagnetic simulation result and is found in close approximation with each other.
Robust optimization design of brushless electrically excited synchronous machines (BEESMs) is a problem that has received extensive attention. The increase in finite element calculation cost due to the increase in the number of motor parameters is one of the main problems faced by optimization. In this paper, a robust multi-objective optimization design method of BEESM based on an improved hill-climbing algorithm is proposed. All design parameters are divided into three subspaces according to the sensitivity by the sensitivity analysis method combined with Kendall's rank coefficient, thereby reducing the consumption required for FEM calculation. The screening problem of Pareto frontier solutions is solved by an improved hill-climbing algorithm. The candidate points to be optimized are screened through the improved climbing algorithm, and only the candidate points located on the Pareto frontier will be optimized, which ensures the high performance of the candidate points. Based on the noise problems that may occur in actual production and processing, the candidate points are robustly analyzed, and the optimal design is screened out. The robust optimization design method proposed in this paper can reduce the computational cost and improve the robustness of the motor based on improving the performance of the motor.