A new miniaturized microstrip branch-line coupler with wide suppression band is proposed in this paper. The new structure has two significant advantages, which not only effectively reduces the occupied area to 12.3% of the conventional branch-line coupler at 0.6 GHz, but also has high 11th harmonic suppression performance. The measured results indicate that a bandwidth of more than 125 MHz has been achieved while the phase difference between S21 and S31 is within 90° ± 1.0°. The measured bandwidths of |S21| and |S31| within 3 ± 0.4 dB are 145 MHz and 150 MHz, respectively. Furthermore, the measured insertion loss is comparable to that of a conventional branch-line coupler. The new coupler can be easily implemented by using the standard printed-circuit-board etching processes and is very useful for wireless communication systems.
This work presents an approach for the design of a quad-band substrate integrated waveguide (SIW) bandpass filter based on multilayer process. TE101/TE102/TE103/TE104 modes are used to characterize the four passbands, respectively. Firstly, the locations and band ratios of the passbands are chosen based on the effective width-length of the SIW resonator and its ratio. Then, vertical couplings of the modes and source-load are designed on the middle metal layers between the dielectric layers, which provides a relatively independent bandwidth tuning and high selectivity. To demonstrate the proposed design method, a quad-band SIW bandpass filter is fabricated and measured. Experimental results agree well with the simulated counterpart. The proposed quad-band SIW filter presents good selectivity and compact size.
Ground penetrating radar is an effective nondestructive method for exploring subsurface object information by exploiting the differences in electromagnetic characteristics. However, this task is negatively affected by the existence of ground clutter and noise especially if the object is weak or/and shallowly buried. Therefore, this paper proposes a novel method for suppressing the clutter and background noise simultaneously in both flat and rough surfaces. First, the ground clutter is removed mainly by applying a simplified least square fitting background method, which remains the residual random noise signal. The remaining signal is then decomposed by singular value decomposition, which assumes that the decomposed signal contains four main components including strong target, weak target, very weak target, and accumulated noise signals. The powered singular values and their differences are clustered by K-means to extract the target signal components. The simulation results indicate that the proposed method is able to enhance the target signal with satisfactory results under both flat and rough surfaces as well as in a high-level background noise. Besides, this method also shows its superiority to the latest existing proposed methods.
D-dot sensor is a type of differential sensor that is widely used in the measurement of ultra-wide band (UWB) pulse electric field. The output of the sensor needs to be integrated to rebuild the original electric field. According to the methods of integration, the measurement system based on D-dot sensor can be classified into software integral D-dot measurement (SIDM) system and hardware integral D-dot measurement (HIDM) system. For an SIDM system, the accuracy of calibration, which is influenced by the integral error of the recovery signal, unfortunately, remains an impediment to its practical application. In this paper, a calibration uncertainty evaluation method based on a standard field generating equipment of time-domain electromagnetic pulse is investigated. The level of the integral error is determined by constructing a noise model using the calibration method. In the process of modeling, the characteristics of the background noise are analyzed first. Additionally, a random signal model taking background noise into account is built, and the integral value of the background noise is derived. Moreover, the integral error model is verified by a statistical method using tested data. After modeling, the uncertainty of the equivalent area for a real D-dot sensor in a software integral system and the methods for reducing the uncertainty are illustrated according to the integral error model.
L-band one-dimensional (1-D) synthetic aperture radiometer is a passive microwave imager that aims to produce global sea surface salinity and soil moisture maps. Two instrument concepts for the L-band 1-D synthetic aperture radiometer have been proposed and selected as candidate payloads for future Chinese space missions, including MICAP (Microwave Imager Combined Active and Passive) for the Chinese Ocean Salinity Mission and IMI (Interferometric Microwave Imager) for the Water Cycle Observation Mission (WCOM). For a synthetic aperture radiometer, spatial imaging error is defined as the difference between the original brightness temperature (BT) and the retrieved BT images within the alias-free field of view (AF-FOV). The main causes of image spatial error in the L-band 1-D system are antenna elements spacing and antenna patterns error. Flat target transformation (FTT) algorithm is always useful for correcting radiometer imaging, but there is still a concave residual error in the retrieved image. An improved calibration algorithm is proposed, which replaces the cold sky view in the FTT with a stable reference scene BT image. A task simulator has been set up to evaluate the new method. The proposed calibration algorithm is shown to reduce the spatial bias and improve the quality of the retrieved BT image.
An ultra-wideband microstrip bandpass filter which operates from 3.1 GHz to 10.6 GHz, with high selectivity and sharp notched band is presented and experimentally verified. The filter is composed of a square loop shaped defected ground structure, metal faces, and microstrip lines. By adding two short stubs connected by a short circuit point on the microstrip lines, the filter achieves an attractive capacity in out-of-band rejection. By placing open stubs in microstrips, the filter realizes a notched band in passband. To illustrate the possibilities of the new approach, an ultra-wideband microstrip bandpass filter is designed and fabricated. Measured results agree well with the predicted counterparts.
In the paper, a universal compensation method is presented to improve the imbalance of a trans-directional coupled-line (TRD-CL) based balun caused by the inevitable physical separation between the TRD-CLs. Using this method, the input mismatch and output imbalance can be effectively solved. Moreover, since the compensation is achieved by shortening the two TRD-CLs instead of adding additional stubs, size miniaturization is maintained. Design formulas are derived using the signal flowchart and even-odd mode analysis. A prototype operating at 1.6 GHz is also designed and measured to verify the proposed method.
Design of a resistive-loaded Transverse Electromagnetic (TEM) horn antenna for air-coupled ground penetrating radar (GPR) is proposed in this paper. As the focus is on the application in sensing pavement subsurface, some issues should be considered, such as ultra-bandwidth (UWB) performance, air-coupled detection, high fidelity, compact structure, and simple fabrication. The resistive-loaded horn antenna with a microstrip-type balun was constructed and measured to facilitate the issues. With the radiation towards concrete ground at a height of 0.5 meters, the measured results suggested that the impedance bandwidth of the antenna was 0.5~14 GHz with a return loss less than -10 dB. The radiation waveform of the horn antenna also showed a late-time ring. A radar experiment result showed that the antenna performed excellently for pavement layer detection.
This research proposes a novel method based on generative adversarial network (GAN) and hidden Markov random field (HMRF) models, for use in large-scale high-resolution synthetic aperture radar (SAR) images. The method consists of three stages. In the first stage, a virtual target and a SAR image are generated by using the GAN model, according to the statistical and gray-level features of the original SAR image used in detection. In the second stage, the virtual target is embedded in the generated image. In the third stage, real targets are detected in the generated image by using the HMRF model. The experiment results show that the proposed algorithm based on GAN and HMRF models can be applied to ship detection in high-resolution SAR images, with high accuracy and processing speed.
In severe multipath channels, depolarization of wireless signals has been shown to be a three dimensional effect. This work herein presents and applies a 3D Stokes vector framework for such depolarization. Empirical data are used to illustrate the capabilities of this framework (specifically, polarization purity indices and direction of propagation) to describe depolarization behavior for three different wireless channels.
Conical scanning radiometric imaging system is good at large field view but suffers from visual nonlinear distortion. The distortion is caused by azimuth and elevation sampling in sphere coordinate, especially for short range and large views. An outdoor experiment is carried out on a building, and the raw image is obtained with obvious distortion. The key to correct distortion is solving the range in relationship between sphere coordinate and Cartesian coordinate. For the a specific building, it is approximately treated as a plane object, and its height is assumed known to solve the range and parameters for plane fitting. Once the coordinates of all pixels are determined, the object is represented in Cartesian coordinate, and the nonlinear distortion is corrected. If any size information for object is unknown, an arbitrary plane is also competent for distortion correction. The difference is that the correcting result is a projection onto this plane instead of real location. However, the projection is also compatible with human vision.
In plasma physics, the interaction with electromagnetic waves is related to the electrons contained in the plasma. So to analyze this interaction, the behaviour of electrons contained must be understood and modeled. In this paper, a new TLM formulation for dispersive media called the exponential time differencing (ETD) transmission line matrix (TLM) technique is introduced to model the interaction with dispersive media. To verify the high accuracy and efficiency of this method, the reflection and transmission coefficients of electromagnetic wave through a non-magnetized collisional plasma slab are computed and compared to the analytical solution. As the electron density in plasma can be distributed as Epstein formula, and its distribution is a function of the grads coefficient σ, and the effect of this parameter and the electron collision frequency νc on the reflection coefficient is calculated. The results show that with different values of σ and νc, the reflection coefficient is affected and can be reduced.
A novel compact ultra-wideband (UWB) bandpass filter (BPF) with quad-notched bands and wide upper-stopband performance using quad-mode stepped impedance resonator (QMSIR) is proposed in this paper. Firstly, the resonance properties of the proposed QMSIR are studied. The proposed QMSIR is found to have the advantages of introducing quad notched bands and wide upper-stopband performance. Then, the proposed QMSIR is employed to achieve four desired notched bands. To validate the design concept, a novel super compact UWB BPF with quad notched bands respectively centered at frequencies of 5.2 GHz, 5.8 GHz, 7.0 GHz, and 8.0 GHz is designed and measured. The predicted results are compared with measured data, and good agreement is reported.
A miniaturized TM21 mode circular patch antenna is introduced. The miniaturization is realized by loading the patch with four symmetric radial slits, which facilitate elongating the current path and thus reducing the resonant frequency and the patch size. In particular, the eigenvalue of the proposed higher order mode is reduced to that of a conventional dominant TM11 mode antenna, resulting in about 40% reduction in the radius. The effects of the slit geometry on miniaturization and resonant frequency are studied. The measurement results are also presented, which are in good agreement with the simulation ones. Such miniaturized TM21 patch antennas with conical radiation patterns have manifold applications in phased array antennas for booming communication demands.
In order to solve the high harmonic content of permanent magnet synchronous motor (PMSM) for fitness car, a PMSM with built-in permanent magnet bridge is proposed in this paper. Compared with surface mounted permanent magnet synchronous motor (SM-PMSM), the proposed motor with permanent magnet bridge structure has lower harmonic content. The performance and magnetization angle of the proposed motor are compared and analyzed in detail. The results obtained from finite element analysis show that the permanent magnet bridge can increase the air gap magnetic field intensity, and different directions of magnetization will affect the amplitude of fundamental wave of air gap magnetic density. Moreover, it can reduce the total harmonic distortion (THD) and make the magnetic density waveform more sinusoidal. It is very beneficial to the smooth output of torque of fitness car.
The paper presents a new method of dispersion compensation. It aims to reduce the dispersion effect of the wave throughout its propagation in the cable. The main objective is to improve the defects localization accuracy in electrical cables. This suggested method can be applied to any test signal injected in the line under test.
A compact dual-band substrate integrated waveguide (SIW) crossover with high isolation is proposed. Two identical slots are etched on the ground plane to achieve dual-band response and compact size. The passbands are generated below the cutoff frequency of the SIW due to the electric dipole behaviour of the slots. In-line ports are also employed to obtain good transmission and high isolation. To validate the concept, a dual-band crossover operating at 2.4 GHz and 5.4 GHz is designed, fabricated, and measured. The crossover size including in-line ports is 43.2×43.2 mm2, equivalent to 0.43λg×0.43λg, here λg is the guided wavelength at the first operating frequency. The tested insertion loss and isolation at the two operating frequencies are smaller than 0.27 dB and greater than 40 dB, respectively.
In this paper, an antenna composed of an inverted L-shaped feeding strip and a shorting strip with three branches for LTE/WWAN mobile phones is presented. With the help of novel ground plane slots, the proposed antenna can realize miniaturization (34×15 mm2) and multiband to cover LTE/WWAN bands. The measured bandwidth (3:1 VSWR) of the proposed antenna is 156 MHz (810-966 MHz) at the low band and 1937 MHz (1548-3485 MHz) at the high band. Moreover, the lowest measured radiation efficiency of the fabricated antenna is more than 54% in the whole operation band. The proposed antenna has been successfully fabricated and measured, and there is a good agreement between simulated and measured results.
In this paper, a 60-GHz broadband 8-by-1 gap-coupled microstrip antenna array is presented and experimentally investigated. The proposed antenna array has been implemented using a Miniature Hybrid Microwave Integrated Circuits (MHMIC) fabrication process on a thin ceramic substrate with εr = 9.9, and h = 127 μm. For a comprehensive characterization and to accurately evaluate losses, as well as manufacturing tolerances, the proposed antenna array structure has been implemented using two different feeding techniques. The first one adopts a grounded broadband via-hole less transition from coplanar to microstrip line (GCPW-to-MS), while the second one has involved a broadband waveguide (WR12) to microstrip transition, based on a ridged waveguide concept. The obtained results have demonstrated that the proposed gap-coupled array configuration provides an improved bandwidth (4.56%) and an enhanced gain (11.8 dBi), while maintaining a lower side-lobe level (13.4 dB). These outstanding performances make the proposed WR12 gap-coupled array structure a potential candidate for the future emerging 60-GHz short-range point-to-point wireless communication systems.
This paper presents the realization of Nonstandard Finite Difference Time Domain (NS-FDTD) analysis having high accuracy and low computational cost to a negative permittivity metamaterial wire medium for the first time. A sine wave of frequency less than that of plasma frequency of the medium which is in the shape of a slab reflector is allowed to interact after identifying the exact values of the required stability condition of the NS-FDTD. The electric field distribution around the plasma slab obtained for a particular excitation point using NS-FDTD and standard FDTD are demonstrated which show obvious advantages of this high accuracy algorithm. This novel technique may be further extended to various dispersive and metamaterial structures.