In this paper, a quarter circular sector with an inverted L shaped monopole antenna for tri-band applications is proposed. The antenna is designed from a U shaped ultra-wideband (UWB) antenna. The number of higher-order modes, each with wide bandwidth, gets excited in a monopole, which electromagnetically couple to provide UWB. In the proposed tri-band antenna the electromagnetic coupling between higher-order modes is reduced by selectively removing the symmetrical portion and decreasing the thickness of the UWB radiator. An inverted L strip is added to a quarter circular sector, and a similarly shaped parasitic element is placed close to the radiator to achieve the desired tri-band. The antenna provides S₁₁ ≤ -10 dB over 2.1-2.5 GHz, 5.0-5.6 GHz and 8.4-9.0 GHz which covers 3G, Wi-Fi, LTE, Bluetooth, WLAN and X- band applications. The antenna offers nearly omnidirectional radiation pattern in the lower band and directional radiation pattern in the other two bands, The prototype antenna is fabricated on a 0.147λ₀×0.22λ₀ FR4 substrate, where λ₀ is the free-space wavelength corresponding to 2.1 GHz. The measured results agree with simulation ones.

A typical outcome of Collaborative Beamforming (CB) in Wireless Sensor Networks (WSNs) is the presence of relatively high radiation in undesired directions, an aspect attributed to the usual random arrangement of collaborating sensor nodes. High radiation in undesired directions and prominent sidelobes are bound to result in interference in adjacent co-channel networks. Research towards suppression of radiation in undesired directions in CB is active with a number of proposals already in place. Most of the proposals are in the domain/perspective of 2-dimension WSN configuration with a focus on suppressing the highest-leveled (peak) sidelobe only. Commonly, peak sidelobe suppression is achieved through nodes' transmission amplitude perturbation after a conventional phase steering based beamsteering procedure. In this paper, concurrent amplitude and phase perturbation at collaborating nodes has been utilized towards achieving concurrent beamsteering and suppression of radiation in an elaborate set of undesired directions. A variant of the Particle Swarm Optimization (PSO) algorithm has been applied in the node transmit amplitude and phase perturbation process. Selection of radiation suppression directions is done uniformly from the set of all possible undesired radiation directions. A WSN featuring planar node arrangement with the sink at an elevated plane has been used as the analysis platform. The proposed scheme outperforms the peak sidelobe suppression approach in terms of observed radiation in undesired directions and average sidelobe levels. It has also been established that increasing the number of collaborating nodes and/or the number of selected undesired radiation directions in the proposed CB scheme leads to undesired radiation performance improvement although at an exponentially decaying rate.

This paper proposes a novel coaxial magnetic gear (CMG) with eccentric permanent magnet structure and unequal Halbach arrays for achieving sinusoidal air-gap flux density and high output torque. The proposed model has a high temperature superconducting (HTS) bulks to replace the epoxy resin in the conventional stationary ring. According to the Meissner effect and one-sided field, the HTS bulks could enhance the modulation effect. The permanent magnets (PMs) on the inner and outer rotors are distributed in Halbach array, in which the PMs are arranged regularly on the outer rotor, and the inner rotor is an eccentric structure. So the inner nonuniform air gap can be obtained. The proposed model with the pole pairs of 4 and 17 for the inner and outer rotors is established, and using finite element analysis (FEA) a calculated torque is up to 350.8 N.m. It is 2.16 times of the torque of conventional CMG.

In this letter, a 120-220 GHz fourth-harmonic mixer based on Schottky diodes is presented. To broaden the bandwidth, a novel diplexer is proposed, which consists of two low-pass filters (LPFs) and a beam lead capacitor. Thanks to the high-pass characteristic of capacitor, the 30-55 GHz local oscillator (LO) signal is efficiently pumped to the diodes. Moreover, a two-level hammer-head configuration is adopted at the LO LPF to block the 120-220 GHz radio frequency (RF) signal. Finally, a 120-220 GHz fourth-harmonic mixer is fabricated and measured. The measurement results show that the conversion loss ranges from 12 to 18 dB within a wide RF relative bandwidth of 58.8%.

A miniaturized in size linear multiple-input multiple-output (MIMO) antenna array operating on demand at 28 GHz and 24.8 GHz for 5G applications is presented and investigated in this research work. The antenna array has the capability to switch and operate efficiently from 28 GHz to 24.8 GHz with more than 15 dB gain at each frequency, having 2.1 GHz and 1.9 GHz bandwidth, respectively. The unit cell of the proposed antenna array consists of a transmission line (TL) fed circular patch connected with horizontal and vertical stubs. The vertical stubs are used to switch the operating frequency and mitigate the unwanted interaction between the adjacent elements of the antenna array to miniaturize the overall dimension of the array. The proposed antenna array is compared with the recent works published in the literature for 5G applications to demonstrate the features of miniaturization and high gain. The proposed array is a potential candidate for 5G sensors applications like cellular devices, drones, biotelemetry sensors, etc.

This letter proposes a novel analysis and design method of a continuously adjustable bandpass combline filter. It investigates the feedline design specifications and introduces an external quality factor (Q_ext) tuning structure to achieve a constant fractional bandwidth over 60% tuning bandwidth. The design approach allows to determine the optimum feedline structure for the filter andis verified by full-wave simulation and measurement. The results show a constant fractional bandwidth of 4.5% over the entire operating frequency range between 225-400 MHz.

In this study, a Vernier effect based temperature sensor with ultra-sensitivity and high-resolution detection is presented. The structure of the proposed temperature sensor is based on dual cascaded Fabry-Perot interferometers (FPIs), which consists of polymer and air cavity FPIs. The polymer cavity works as the sensing part, whereas the air cavity works as the reference part. The slight difference between the Free Spectral Range (FSR) of the sensing and the reference FPIs can establish the Vernier effect, which improves the sensitivity of the cascaded FPIs structure compared to the single FPI structure. The experimental results show that the proposed structure can provide the ultra-high temperature sensitivity of 67.69 nm/˚C that is 20 times higher than the single FPI, which is 3.36 nm/˚C in the testing range of 26˚C-28˚C. In addition, the structure is simple to fabricate, compact, inexpensive, along with ultra-sensitivity and high-resolution. Therefore, the proposed sensor is a suitable choice for the applications demanding high resolution temperature detection in different fields of engineering and science.

An optical fiber sensor based on thin-core fiber (TCF) and no-core fiber (NCF) interference structures is presented and experimentally demonstrated to measure the curvature and temperature. The fabrication process of the sensor is simple and convenient, and the sensing part is formed by cascading a TCF and an NCF between two single-mode fibers. The dips at resonant wavelengths are generated in the optical transmission spectrum owing to mode interference. The experimental results indicate that an optical curvature sensitivity of -5.76 nm/m^-1 is achieved in the linear range of 0.9895-3.2817 m^-1, and that a temperature sensitivity of 0.18 nm/˚C is obtained in the temperature range of 25-55˚C. Additionally, the cross-sensitivity problem is solved using the coefficient matrix measurement method, and the cross-sensitivity is as low as 0.0312 m^-1/˚C. Therefore, the sensor exhibits a highly reproducible technique and low cross sensitivity, which has a wide range of application prospects in the accurate measurement of mechanical arms and structural health monitoring.

In this paper, a miniaturized dual-band circularly polarized (CP) implantable antenna is proposed. The -10 dB impedance bandwidth of the antenna in Industrial Scientific Medical (ISM) band and the low frequency part of UWB can reach 30.3% (2.02~2.74 GHz) and 39.9% (3.73~5.59 GHz), respectively. The important features are its CP characteristic in two bands and a small volume. The miniaturization of the antenna is realized by half-cutting technique, which is to cut the original antenna meeting the symmetry of structure and electric field distribution into two halves to obtain a compact structure and wider impedance bandwidth, so that the final size is 5×10.4×0.254 mm³. The CP wave performance of the antenna is achieved by exciting orthogonal polarization components on the radiation surface. The proposed antenna provides an axial ratio of less than 3 dB. CP axial ratio bandwidths in the two bands are 24.4% and 18.1%, respectively. In addition, the safety considerations and link margin are evaluated to analyze the performance of the proposed antenna. In order to verify the simulation results, the proposed antenna is fabricated. The measurements are carried out under the human muscle mimicking liquid circumstances. The measured data are in good agreement with the simulation results.

In the paper, a very compact UWB-MIMO antenna with four rejected bands property is introduced and investigated. With a T-shape stepped stub on back ground, impedance bandwidth of 3-11 GHz and isolation of -15 dB are achieved. By etching four pairs of symmetrical L-formed slots into the radiators, four bands are isolated. With only a size of 21 mm × 27 mm, the proposed UWB-MIMO antenna system has low port coupling of -15 dB and wide working bandwidth of 3-11 GHz (S₁₁ ≤ -10 dB or VSWR < 2) except 3.5 GHz WiMAX band, 5.3 GHz lower frequency band of WLAN, 5.8 GHz upper frequency band of WLAN and 7.4 GHz X-band. Moreover, other characteristics, such as radiation patterns, antenna gain, antenna efficiency, and ECC (envelope correlation coefficient) are also studied.

This paper proposes a 2D semi-analytical electromagnetic model to compute the magnetic field and eddy current generated by a variable current density along a conducting billet of induction heater. The developed model is based on the combination of the discretization method and the Biot-Savart theory. Firstly, the analytical solutions of the vector potential and the magnetic field are calculated in all elements discretized cylindrical geometry using the law of Biot-Savart. Then, the total field is determined by the contribution of the superposition of each element of the discretized geometry. The eddy currents are computed using the Ampere law, and it also allows us to determine the exact resulting heating power density, which is the heat source of the thermal problem. The results obtained are in agreement with those obtained using finite element method. Therefore, the developed magnetic model presents a fast and accurate tool for the design of induction heating devices.

A compact microstrip rat race attained by artificially shortening its lines by inserting stubs is presented. The design starts with a preliminary theoretical length reduction where quarter wavelength lines are shortened thanks to shunt open circuit stubs placed in the line mid-points. Such a preliminary design is then optimized via particle swarm optimization (PSO) within a full wave electromagnetic CAD, also bending the stubs to attain maximum compactness. The resulting design occupies an area up to only 37% of a conventional rat race, with performances comparable to those of a standard rat race.

This research work deals with the plane wave diffraction by a coated perfect electrically conducting wedge with arbitrary apex angle. The uniform layer covering the impenetrable wedge is made of a standard double positive material or an unfamiliar double negative metamaterial with negative permittivity and permeability at the operating frequencies. The propagation mechanism is studied when the incidence direction is perpendicular to the edge of the composite structure, and uniform asymptotic solutions are proposed to evaluate the diffraction contribution for both the polarizations. Such approximate solutions are obtained by using the Uniform Asymptotic Physical Optics approach based on electric and magnetic equivalent surface currents radiating in the neighboring free space. The related expressions are user-friendly and provide reliable field values as verified by numerical tests involving a full-wave electromagnetic solver.

This paper aims to present a highly selective, compact size new ultra-wideband (UWB) bandpass filter with three sharp notches for UWB indoor applications. The fundamental geometry of the filter is based on modified multi-mode resonator (MMR) structure which comprises a open-ended step impedance resonator (SIR) attached to an interdigitated uniform impedance resonator (UIR). Realizing a Comb-shaped resonator structure below the UIR and symmetrically extending the lower arm edge of the interdigital coupled lines, three notches are generated at 6 GHz, 6.53 GHz, and 8.35 GHz. These notches have improved the UWB bandpass filter responses by suppressing the existing interferences in the UWB passband created by Wi-Fi 6E (6 GHz), super-extended C band (6.425 GHz~6.725 GHz), X band satellite communications for satellite TV networks or raw satellite feeds (7.25 GHz~8.395 GHz). Concurrently the notched band filter has achieved superiority in other salient features concerning passband and stop band of the filter such as a high passband fractional bandwidth (115.76%), low return loss (-13.27 dB), low insertion loss (0.44 dB~0.97 dB), wide upper stop band (5.37 GHz), nearly flat group delay (0.28 ns~0.45 ns) etc. The ultimate design of UWB bandpass filter is fabricated and verified by comparing the simulated filter responses with the measured results indicating a good agreement.

Directed energy weapons provide a number of useful functions for the modern fighting force, and hence it is useful to produce a framework in which such a weapon's performance can be predicted. Towards this objective this paper introduces a new stochastic model to determine the number of targets defeated by a directed energy weapon over a given time interval. The key to this is to introduce a general queueing model, where arrivals are modelled by a renewal process, and the service time of a target being affected by the weapon is related to its probability of defeat. The queue is assumed to have an infinite capacity, and it is shown how the waiting time of detected threats can be modelled by an auxiliary delay process. A random variable counting the number of targets processed by the queue is then defined. Several functions constructed from this random variable will be investigated in order to identify a suitable metric for assessing performance. In order to facilitate this an example where a high energy laser is used for threat defeat is examined to investigate the utility of the identified performance metrics. As will become apparent, the modelling framework has considerable utility due to the fact that it can be used for performance prediction of any weapon system where an arrival process of threats and corresponding probability of defeat can be specified.

In this paper, an efficient wideband array adaptive beamforming (ADBF) approach based on keystone transform is presented. In order to eliminate the aperture effect of the wideband signal, the modified keystone transform is applied to remove the time delay between different array elements. Thus, the wideband array is equivalent to the narrowband array, and the orthogonal projection matrix of the target steering vector can be used to filter the desired signal in the training samples, which avoids the signal cancellation caused in the estimation of ADBF covariance matrix. Compared with theestablished algorithm of sliding window, this approach can significantly reduce the computational burden. The feasibility and effectiveness of the proposed method are validated through numerical simulations.

This paper proposes a joint estimation algorithm based on sparse-Bayesian learning (SBL) for the gain-phase problem between array antenna channels. The algorithm uses the idea of the iterative method to jointly estimate the direction-of-arrival (DOA) and gain-phase error calibration coefficients in the iterative process, combining self-calibration and calibration with a calibration source. At each iteration, the rough value of DOA is first estimated using SBL, and then the DOA estimate is used to calculate the gain-phase error calibration coefficient. The value obtained in each iteration is brought into the error cost function, which is constructed based on the principle of signal and noise subspace orthogonality. Iterations are continued until convergence to find the minimum value of the cost function. The algorithm does not require a priori knowledge of array perturbations and has good performance in DOA and array gain and phase error estimation. Simulations and experimental measurements show that the method has better calibration performance than other methods based on optimization algorithms, and the algorithm effectively improves the antenna gain.

A W-band high isolation single-balanced mixer using a 0.1-um GaN high-electron mobility transistor process is proposed in this paper. The diode is biased near the threshold voltage to reduce drive level, and the needed LO power is only 3 dBm. Moreover, the reasonable diode layout and phase compensation structure are used in the proposed mixer to enhance the LO-to-RF isolation. The measured results of the proposed mixer demonstrate a single-sideband conversion loss of 9-10.6 dB and a LO-RF isolation of 40 dB from 75 to 110 GHz with 7 dBm LO power. Moreover, a DC-to-18 GHz IF bandwidth is achieved with the LO frequency fixed at 110 GHz. The 1 dB compression point of the proposed mixer is 11 dBm with 16 dBm LO power. The measurement results indicate that GaN mixer has great potential for W-band transceiver system applications.

Implementation of a broadband Ruthroff-type transmission line transformer balun with a 1:2 step-up impedance transformation ratio is presented in this letter. The proposed Transmission Line Transformer (TLT) balun was investigated with broadside-coupled lines using three stacked microstrip lines. The proposed balun was formed by cascading one section of modified Ruthroff-type 2:1 unbalanced-to-unbalanced TLT with one section of Ruthroff-type 1:4 TLT balun in series. The achieved fractional bandwidth of the balun is 192.17% over the frequency range from 1.2 to 6.6 GHz, which covers the IEEE 802.11 a/b/g WLAN, WiMAX applications. The measured amplitude and phase imbalances are less than 1 dB and less than 4.51˚, respectively at this frequency range.

In this manuscript, plasmonic metal conductors such as Silver, Gold, Aluminum, Copper, Chromium, Tungsten, Titanium, and Nickel are investigated on a T-shaped nano dipole antenna using dielectric materials such as Silicon Dioxide, Zinc Oxide, Indium Tin Oxide, and Silicon Nitride. The optical properties of the conductors and dielectric materials are modeled using Drude and Lorentz dispersive models, respectively. It is observed that the Aluminium metal supports high quality plasmonic oscillations for a wide range of Terahertz frequencies. The Aluminium metal also shows high losses occurring at the Terahertz frequency among the other metals. The Gold and Silver can resonate in the visible region and have moderate losses compared to the other plasmonic metals. It is noticed that the near-zero permittivity point of the Silicon Dioxide substrate occurs at 2875 THz which is much greater than the other three substrates. Further, it is observed that on the Silicon Dioxide, Zinc Oxide, and Silicon Nitride substrates the Silver Nano dipole antenna shows the maximum directivity of 6.615 dBi, 5.671 dBi, and 5.709 dBi, respectively. The Aluminium nano-antenna gives the maximum directivity of 5.066 dBi on the Indium Tin Oxide substrate. The Silver-Silicon Dioxide Nano-antenna will be suitable for the terahertz optical wireless communication.