A compact stepped-impedance dipole antenna with harmonic suppression is presented. The antenna occupies an overall size of 40 x 12 x 1.6 mm³ when being printed on a substrate with a relative dielectric constant of 4.4 and loss tangent 0.02. The simulation and experiments are well matched and offer a 2:1 V SWR (S₁₁ < -10 dB) bandwidth of 590 MHz at 2.45 GHz. In comparison with a conventional strip dipole, the stepped impedance based dipole antenna shows complete suppression of the first and second harmonics making it suitable as an efficient EMI emission free antenna for widely used Bluetooth and WLAN applications. It can also be employed for wireless power transfer applications with more efficiency.

In this letter, a compact microstrip bandpass filter (BPF) with four transmission zeros (TZs) is designed by using a short-stub centered loaded folded dual-mode resonator and an I/O mutual coupled open-stub loaded feedline structure. The coupling structure can realize source-load (S-L) coupling with quadratic function coupling coefficient, which can generate three TZs in the upper-stopband to improve the selectivity. Owing to the intrinsic characteristics of the dual-mode resonator, one extra TZ can be created near the lower passband edge. Finally, a compact BPF with fractional bandwidth (FBW) of 3.5% located at 2.4 GHz for WLAN application has been designed and fabricated. Good agreement between simulation and measurement verifies the validity of the design.

In this paper, a novel wideband dual-band dual-polarized magneto-electric (ME) dipole antenna is proposed. The proposed antenna consists of a folded double-layer magneto-electric dipole, a stair-shaped feeding line with a balun structure and a rectangular box-shaped reflector. The folded double-layer magneto-electric dipole is able to generate two resonant frequencies. The polygon balun structure can better match the antenna impedance. The rectangular box-shaped reflector not only can suppress antenna's back radiation but also can realize high gain over the operating frequencies. Both simulated and measured results show that the antenna can obtain two wide impedance bandwidths of 60% (1.54-2.87 GHz) in lower frequency band and 27% (4.62-6.10 GHz) in higher frequency band with the reflection coefficients lower than 10 dB for both input ports. The isolation between ports is greater than 25 dB in the corresponding frequency band. The gains of the measured antenna were 8.5-9.7 dBi in the low frequency band and 8.5-11.5 dBi in the high frequency band, respectively.

This letter presents a novel differential filtenna for microwave systems at 2.4 GHz on planar technology. This filtenna exhibits 5% bandwidth with a 3-pole Chebyshev response. The filtenna uses a square patch as radiating element combined with λ/2 resonators. Experimental and simulated return losses are presented with good agreement. Moreover, the experimental common and differential mode radiation patterns are presented showing an attenuation greater than 15 dB for the common mode.

Non-contact vibration detection using microwave radar is becoming a popular research area. However, vibration sensing using Doppler radar based measurements suffers from the problem of `Null point'. In order to mitigate this, traditional designs incorporate phase measurements using Quadrature (I/Q) radar. Such Quadrature radars are not cost effective for large scale indoor deployment scenarios. In this paper, we propose a new configuration of `Indented Radar'; a system of two singlechannel radars offset in space by a path length, which is equivalent to 90 degree phase shift. However, such a system of two independent channels is prone to different imbalances such as amplitude, phase and DC. This work closely examines the imbalance effect on the two-radar system and reports a novel approach that can be used to tackle such imbalance in a two-radar configuration. Our approach yields superior results over other commonly used I/Q algorithms, while measuring vibrational frequencies. Thus, our work can find immense application in both vital sign detection and structural vibration detection use-cases where affordable solution is sought.

Microwave radar imaging is increasingly being used in infrastructure monitoring applications due to its low cost, rapid measurement time, non-contact characteristics, and ability to penetrate nonmetallic media. An appropriate waveform design must be designed to obtain accurate information on the targets observed or the features being probed. Ultrawideband (UWB) radio frequency (RF) noiselets are excellent candidate waveforms in view of their multiresolution and interference rejection features. In this paper, a waveform optimization approach for UWB noiselet waveforms is described to achieve high peak-to-sidelobe ratio (PSLR) to enhance imaging capabilities. Synthetic aperture radar (SAR) scanning for microwave imaging is introduced after analyzing the essential microwave approaches for the multilayered structure. Image reconstruction using SAR scanning is performed for various multilayered structures and quasi-3D images of these structures are presented for nondestructive testing and evaluation (NDT&E) applications.

Substrate integrated waveguide (SIW) is widely used in filter design due to its advantages of high Q value, high power capacity, small size and easy integration. In this paper, a symmetric folded substrate integrated waveguide (SFSIW) miniaturization method is proposed. Through the comparison of the miniaturization degree of the resonant cavity before and after folding, the feasibility of this method is verified, and the miniaturization theory of SIW filter is further improved. Using a symmetrically folded SIW resonator, a two-cavity filter and a three-cascaded cross-coupling filter were designed. This structure achieves better miniaturization of the filter. The high Q value of the SFSIW resonator makes the filter's insertion loss smaller, the transmission characteristics better, and the simulation and measurement results are consistent.

A novel coplanar waveguide fed compact dual-band antenna for 2.5/5.7 GHz applications is presented in this paper. The above characteristics are obtained by carefully optimizing the slotted ground planes and meander short placed between the signal strip and one of the lateral ground planes. The proposed antenna has been designed on a substrate with dielectric constant 4.4, thickness 1.6 mm, and it occupies a small area of 18.2×20 mm². The experimental analysis shows 2:1 VSWR bandwidth up to 150 MHz and 370 MHz for 2.5 GHz and 5.7 GHz, respectively. Antenna radiation characteristics, including return loss, radiation pattern, radiation efficiency and gain are also validated with numerical simulation and experimental measurements.

Due to the spatial and temporal distribution of meteorological conditions along the transmission lines, the equivalent model with lumped parameters cannot accurately represent the line model with the actual parameters. In the paper, the nonuniform parameter model based on the dynamic thermal rating (DTR) technology of transmission lines is adopted to establish the power flow analysis model based on the conductor temperature. The algorithm presented in the paper is adopted to analyze the power flow of power networks with known load and meteorological parameters. And then cases with parameters of dierent seasons and spatial distribution in practical conditions are used to verify the feasibility of the algorithm. It is shown that the power flow analysis model established in this paper can realize the accurate analysis of the thermal load capacity of the transmission line in the power grid, which has great practical significance.

Design and development of a novel arrow headed modified cross slot array antenna with dual band characteristics and circular polarisation is reported. The proposed array configuration consists of an array of four arrow headed modified cross slot elements which are electromagnetically coupled by using a 1:4 corporate feed network. The slot elements are etched on the ground plane of the dielectric substrate with a feeding network on the other side. The proposed slot array shows dual band behaviour and enhanced gain characteristics compared to a single element arrow headed modified cross slot antenna. The slot array antenna shows resonance at two frequencies of 1.72 GHz (1.6912 GHz-1.7656 GHz) and 2.45 (2.3656 GHz-2.5568 GHz) GHz with circular polarisation in the upper band. This novel slot array configuration has a measured gain of 6.23 dBi at the lower resonant frequency and 7.01 dBi at the upper resonant frequency. The proposed slot array antenna exhibits bidirectional radiation patterns with improved gains. The simulated results are in good agreement with the experimental ones.

In this paper, the nonlinear single negative metamaterials (NLSNM) based on the microstrip loaded with varactor diodes are investigated. It is found that the NLSNM, including nonlinear epsilon-negative metamaterial (NLENM) and nonlinear mu-negative metamaterial (NLMNM) can be realized by loading varactor diodes and chip inductors onto the microstrip, and their transmission gaps can be controlled conveniently by the signal power. In addition, the nonlinear property of the heterostructure constructed of NLMNM and epsilon-negative metamaterial (ENM) is also studied, and the results show that the transmission property, especially the transmittance of the tunneling peak of the NLMNM-ENM heterostructure can also be regulated by the signal power. The NLSNM may have important potential applications in the microwave switch controlled by the signal power.

This paper deals with the influence of steel non-linearity when calculating the induced current/voltage on a pipeline circuit with earth return under 50-60 Hz induction by power lines or electrified railway lines. By having at disposal the measured curves of the per unit length pipe internal impedance versus the current flowing in it, one can calculate induced voltage and current on the pipeline-earth circuit by means of the successive approximations method. The paper presents some comparison of the results when ignoring or not the steel pipe non-linearity. In certain cases, the differences can be significant.

Accurate analysis of the thermal field in switched reluctance motor (SRM) is critical to the service life and safety performance of the SRM. According to the general structure of SRM, a two-dimensional (2D) finite element analysis (FEA) model was established, and the loss of each component, especially the iron loss, was analyzed by Orthogonal Fourier decomposition method, revealing the characteristics of the loss. A magnetic-thermal one-way coupling method is further used to model the temperature of the SRM, and basic assumptions and reasonable boundary conditions are set. Transient thermal analysis was carried out under natural cooling conditions and high vacuum conditions, respectively, and the results were compared and analyzed to understand the temperature distribution of the main components under two operating conditions.

This article describes numerical solutions for the electromagnetic interactions, known as `wakefields', of a proton beam with an RF cavity and a beampipe. Using FDTD calculations, time-varying electromagnetic solutions are obtained. Unlike modal expansion methods, FDTD allows to compute transient wakefields due to proton beam passing through the structures. A popular time-frequency analysis approach, the short-time Fourier transform (STFT), is applied to the electromagnetic fields inside a resonant cavity and past an open-ended beampipe. STFT enables a more explicit interpretation of the transitions between the fields radiated by moving charges and the resonant modes. The described time-frequency analysis is useful to engineers and accelerator physicists who analyze proton beam dynamics. As an extension of electromagnetic simulations using an extended proton bunch, a numerical Green's function approach is proposed in order to account for the wakefields due to individual superparticles.

Partially dielectric-filled empty substrate integrated waveguide (PFESIW) is introduced for millimeter-wave application alongside partially dielectric-filled ESIW filter by using inverter and resonators technique. The new design presents good transition implementation in order to introduce a waveguide compatible with planar integrated circuits. The main goal of introducing the new transmission line PFESIW is to control characteristic impedance without changing the cutoff frequency. The presented transmission line is analyzed by calculating attenuation constant α, phase constant β and characteristic impedance Z. The PFESIW is used to build a resonator with high-quality factor. The filter based on the combination of of ESIW and PFESIW is proposed. Furthermore, the designed filter showed very good performance in terms of bandwidth and cost. Transmission line and filter prototypes are manufactured using standard printed circuit board fabrication. Partially dielectric-filled ESIW measurement displays very good results in terms of phase constant β, attenuation constant α, return loss (S₁₁) and insertion loss (S₁₂). Measured return loss (S₁₁) and insertion loss (S₁₂) for waveguide and filter agree very well with simulation.

A modified compact microstrip resonance cell (CMRC) low pass filter (LPF) with ultrawide and deep stopband using novel fractal patches is presented. The proposed filter has low insertion loss in the passband, good selectivity, ultrawide and deep stopband. The experimental results show a 3-dB cut-off frequency of 2.85 GHz and out-of-band rejection up to 67 GHz with 181.5% relative stopband bandwidth.

In this paper an ultra-wideband band (UWB) pass filter is introduced. The filter is composed of multiple shorted shunt stubs and defected ground structure (DGS). The defected ground structure is composed of some circular-shape defects and diagonal-line patterns. The bend-shaped defected-ground structure is thoroughly studied and compared to some other defected structures. The filter features a simple structure and small dimensions (12 × 22 mm²). Meanwhile, a systematic design method is presented. The analysis method is based on numerical methods and is verified by a commercially available EM simulator. The 3 dB passband of the proposed wide band filter is between 2 GHz and 10 GHz.

Through-the-wall imaging (TWI) of human vital signs by bioradar is a hot research topic in recent years. Unknown wall parameters (mainly thickness and dielectric constant) are huge challenges for TWI. Ambiguities in wall parameters will degrade the image focusing quality, lower signal-to-noise-clutter ratio (SNCR) of vital signs, cause vital signs to be imaged away from their true positions and blur the close vital signs from multiple humans caused by the imaging resolution declination. A through-the-wall propagation model of vital signs for multiple-input and multiple-output (MIMO) bioradar is first built to analyze the influence of wall on imaging. In order to obtain focused image of vital signs quickly, an imaging model and a novel autofocusing imaging method of vital signs are proposed in this paper. Since vital signs of human are weak and sensitive to interferences, the SNCR-enhanced imagery of vital signs after change detection (CD) is applied to evaluate the focusing quality of image. Reflections of wall in the stationary targets imaging result are line structure approximately, so Hough transform is used to extract the positions of the front edge and rear edge of wall automatically. Propagation time in the wall of electromagnetic waves is estimated and used to build the constraint relationship of wall parameters. The number of unknown parameters is reduced to only one and the efficiency of autofocusing imaging improves. Several cases, including the case of single human, multiple human objects close to each other and the case of non-human objects, are simulated. The magnetic resonance imaging (MRI) image of human chest is put into simulation scene. And then the simulation data of human vital signs are calculated by the finite-difference time-domain (FDTD) method. The results show that the proposed method can effectively estimate the wall parameters and improve the focusing performance of human vital signs. And also the kurtosis of image can be used as a feature to efficiently decide the human vital signs are existed or not. Thus the SNCR of vital signs and resolution of imaging are improved, which are beneficial for detection of vital signs. The position errors of human vital signs are also corrected.

An array of rectangular holes pierced through a conducting screen is treated herein by a rigorous full-wave modal analysis using the moment method entailing Green's functions for rectangular cavities and planar multilayer structures in the spectral domain. Unexpectedly strong diffusions of incident plane waves are observed even at frequencies where the size of each hole is considerably less than the wavelength, posing a transmission efficiency that exceeds unity and thus leading to extraordinary transmission since this defies classical aperture diffraction theory. This paper fortifies the present understanding of the role surface plasmon polaritons (SPP) play in explaining this phenomenon, by using surface-wave dispersion and Floquet lattice diagrams to link up with the peaks in the transmission spectra. The incidence angle and polarization of the irradiation are taken into account in this work.

This paper describes the design of a broadband, fixed-IF, high efficiency single subharmonic mixer at Ka-band. The co-simulation between HFSS and ADS is applied to the modeling of the mixer. In order to improve the accuracy of simulation, the diode model is divided into passive linear model and active nonlinear model. On this basis, a global accurate equivalent circuit model of mixer is proposed and verified by testing data. The circuit of the presented mixer printed on the substrate of Rogers RT/Duroid 3003 is mounted in a waveguide block. When the fifixed IF frequency is set at 1.5 GHz, measured results show that the conversion loss is less than 8 dB over the RF bandwidth from 25 GHz to 39 GHz with 12 dBm of local oscillator power. The minimum conversion loss of 6.2 dB is measured at 28 GHz. The measured isolation between LO and IF, LO and RF is over 23 dB. The measured isolation between IF and RF is over 20 dB. Good isolation is achieved.