Microwave Staring Correlated Imaging (MSCI) technology can obtain high-resolution images in staring imaging geometry by utilizing the temporal-spatial stochastic radiation field. In MSCI, sparse-driven approaches are commonly used to reconstruct the target images when the radiation fields are accurately calculated. However it is challenging to compute radiation filed with high precision due to existence of random phase errors in MSCI systems. Therefore, in this paper, a self-calibration method is proposed to handle the problem. Specifically, a two-step self-calibration framework is applied which alternately reconstructs the target image and estimates the random phase errors. In the target image reconstruction step, sparse-driven approaches are utilized, while in the random phase errors calibration step, an adaptive learning rate method is adopted. Moreover, the batch--learning strategy is utilized to reduce computation burden and obtain effective convergence performance. Numerical simulations verify the advantage of the proposed method to obtain good imaging results and improve random phase errors correction performance.
In this paper, a compact triple-band coplanar waveguide (CPW)-fed patch antenna with dual-polarization characteristics for wireless applications is proposed. The antenna is composed of an F-shaped patch, a grounded-C strip, a rectangular strip, and a horizontal rectangular grounded slot. The first circular polarized band is obtained by the F-shaped feed-line, and the second is achieved by the left C-shaped strip, while the right rectangle strip is responsible for the lower linearly polarized band. By inserting a slot at the right of the square slot, a notched band centered at 5.5 GHz is achieved. Both simulated and experimental results show that the antenna can generate three separate impedance bandwidths to cover frequency bands of 2.4/5.2/5.8-GHz WLAN band and X band. And the antenna is circularly polarized in the 5.8 GHz and 10GHz band. Furthermore, the antenna structure is extremely simple and occupies small space. The proposed antenna has its applications in compact and portable devices operating at multiple frequency bands like cellular phones, Tablets, Wi-Fi devices, etc.
A differentially fed dual-polarized patch antenna with wide bandwidth is presented in this paper using Substrate-Integrated Waveguide (SIW) technology. The antenna comprises a circular patch radiator, a square SIW cavity and four symmetric arc-shaped slots. The circular patch is internally embedded in the square SIW cavity with a surrounded ring slot. Two pairs of differential L-shaped probes are used for the excitation of the differential signals. These signals excite the orthogonal linearly-polarized modes. The dominant resonant mode of the circular patch resonator (TM11) and the modes of the SIW cavity (TE110 and TE120/TE210) are employed to achieve effective radiation under these resonances. Besides, four symmetric arc-shaped slots are etched on the top surface of the cavity to enhance the impedance bandwidth. The resonant properties of these modes are studied based on the cavity model theory. Then, their resonant frequencies are discussed to provide information for designing and optimizing such an antenna. Finally, the feeding positions of the differential L-shaped probes are investigated for good impedance matching. The proposed antenna has been fabricated and measured. The measured results show that the proposed antenna achieves a wide impedance bandwidth of about 64.8% (4.37-8.56 GHz) and 64.2% (4.48-8.72 GHz) for horizontal and vertical polarization, respectively. High differential isolation of better than 30 dB and low cross-polarization are obtained by adopting the differential feeding mechanism. Due to the SIW cavity-backed structure, the antenna shows unidirectional radiation patterns and low back-lobe radiation, making it conveniently integrated with microwave differential circuits and applied in the base station systems.
In this paper, we discuss the spectral property of radiation of an electron moving in a bi-period harmonic undulator field with a phase between the primary undulator field and the harmonic field component. We derive the expression for the photons per second per mrad2 per 0.1% BW of the radiation. A small signal gain analysis is also discussed highlighting this feature of the radiation. A bi-period index parameter, i.e., Λ is introduced in the calculation. According to the value of the index parameter, the scheme can operate as one period or bi-period undulator. It is shown that when Λ = π, the device operates at the fundamental and the third harmonic. However, when Λ = π/2, it is possible to eliminate the third harmonic.
Compressive sensing (CS) is an effective method for reconstructing magnetic resonance imaging (MRI) image from under-determined linear system (ULS). However, how to improve the accuracy of MRI image reconstructed by CS is still a serious problem, especially in noisy conditions. To solve this problem, in this paper, we propose a novel approach, dubbed as regularized maximum entropy function (RMEF) minimization algorithm. Specifically, motivated by the entropy function in information theory, we propose a maximum entropy function (MEF) to approximate Lq-norm (0 < q < 1) as sparsity promoting objectives, and then the regularization mechanism for improving the de-noising performance is adopted. Combining the above two ideas, a new objective function of RMEF method is proposed, and the global minimum is iteratively solved. We further analyze the convergence to verify the robustness of the RMEF algorithm. Experiments demonstrate the state-of-the-art performances of the proposed RMEF algorithm and show that the RMEF achieves higher PSNR and SSIM than other widely-adopted methods in MRI image recovery.
A triple band notch MIMO/Diversity antenna using Inductance Boosted Compact Electromagnetic Band Gap (IB-CEBG) cells is presented in this paper. For obtaining compactness in the conventional EBG cell, spiral shaped defects are introduced. The proposed antenna obtains triple band notches in WiMAX (3.3-3.6 GHz), WLAN (5-6 GHz), and the X-band satellite communication (7.2-8.4 GHz) bands. IB-CEBG cells exhibits miniaturization of approximately 46% for WiMAX band, 50% for WLAN band and 48% for X-band Satellite communication band, compared to conventional EBG cells. To enhance the isolation among all four compact UWB monopoles, rectangular slots in the ground plane and parasitic decoupling arrangement are utilised. Further, a stepped structure with an angular separation of 90˚ is incorporated with individual monopoles to reduce mutual coupling effects. Stepped structure also helps in the better impedance matching by incrementing the path length. The results show that the magnitude of transmission coefficient is greater than 15 dB in between the ports of proposed antenna elements. Envelope Correlation Coefficient is less than 0.5, which lies in tolerable limits for Ultra-Wide band (UWB) frequency range. It has been noticed that notched frequency is dependent on IB-CEBG cell parameters. The proposed antenna is fabricated using an FR-4 substrate with overall dimensions of 58 x 90 x 1.6 mm3.
Using the moment method, we analyze a loop antenna with a perturbation segment in the presence of a ground plane. First, the radiation characteristics versus loop height above the ground plane are investigated. It is found that as the loop height increases to more than 0.2 wavelengths a novel antenna other than a conventional one can exist, showing an enlarged bandwidth of 9% for a 3 dB axial-ratio criterion. Next, the radiation mechanism of the novel antenna is compared with that of the conventional one. Last, the novel loop is used in a comb-line antenna as a radiation element. It is found that the CP wave bandwidth is five times as wide as that of a conventional comb-line antenna. The analysis results are verified by experimental work.
The finite-difference time-domain (FDTD) algorithm is a numerical stencil computation method, which is widely used in solving electromagnetic simulation problems. However, this algorithm is both computing and storage intensive, so the simulation efficiency is usually restricted in software implementation on CPUs. Recently, hardware accelerators have proved to be effective in improving the performance of various stencil computations. In this paper, we propose a hardware architecture of the 3D FDTD algorithm along with a practical convolutional perfectly matched layer (CPML) boundary condition and implement it on a field programmable gate array (FPGA). By applying the chain processing elements array and temporal parallel strategy, the proposed accelerator can achieve a maximum of 608 mega cells per second (Mcells/s), which is approximately 6 times higher than that of other reported designs on FPGAs. Moreover, the accelerator can maintain the speed above 467 Mcells/s for different grid sizes and CPML layers without modifying the hardware design, which demonstrates the performance stability and flexibility of the architecture under various applications.
Magnetic resonance electrical properties tomography has attracted attentions as an imaging modality for reconstructing the electrical properties (EPs), namely conductivity and permittivity, of biological tissues. Current reconstruction algorithms assume that EPs are locally homogeneous, which results in the so-called tissue transition-region artifact. We previously proposed a reconstruction algorithm based on a Dbar equation that governed electric fields. The representation formula of its solution was given by the generalized Cauchy formula. Although this method gives an explicit reconstruction formula of EPs when two-dimensional approximation holds, an iterative procedure is required to deal with three-dimensional problems, and the convergence of this method is not guaranteed. In this paper, we extend our previous method to derive an explicit reconstruction formula of EPs that is effective even when the magnetic field and EPs vary along the body axis. The proposed method solves a linear system of equation derived from the generalized Cauchy formula using the conjugate gradient method with fast Fourier transform algorithm instead of directly performing a forward calculation, as was done in our previous method. Numerical simulations with cylinder and human-head models and phantom experiments show that the proposed method can reconstruct EPs precisely without iteration even in the three-dimensional case.
In this article, a modified circular shape printed dipole structure is studied to achieve wide bandwidth and dual-band circular polarization (CP) behavior along with dual polarizations. The idea behind this structure is that asymmetric geometry can give rise to circular polarization with an optimized position of coaxial probe feed. The circular patches on both sides of the substrate are altered with elliptical slots at an optimized location in association with opening slots. With these alterations the impedance bandwidth for S11<-10 dB is ranging from 2.36-7.34 GHz (4.97 GHz) which is nearly 102.5% about mid-point frequency 4.85 GHz. The antenna resonates at a lower band (1.55 GHz) and shows linear polarization (LP) operation at that band whereas dual CP bands with dual senses are obtained at higher frequency ranges 4.00-4.60 GHz and 6.07-7.13 GHz respectively with 3-dB axial ratio bandwidth of 13.7% and 16.6%. The simulated and measured experimental results are in close agreement. This antenna is suitable to be used for navigation purposes, radar communication, and wireless communication (especially wireless avionics intra communications) in S and C bands, respectively.
First of all we inform the audiences that this article is a Review Paper (RP) for the PIERS17 Proceedings Paper (Zheng et al. ). The reason why we publish this RP is that: although the paper  reported important ideas and simulation facts, details of the contents were insufficient, and the audiences of the report were not satisfied. This was because the page number was limited, and we saved the number of pages. However, because the contents of~ are important, we decided to publish an RP, which would provide additional explanations or give considerations supporting main issues. Now, we start the abstract from Section~1. Here, we mention historical topics and RP-related things. In Section~2, we explain the problem of diffraction by a conically-mounted metal grating. To save the page number, we skip the method of solution. In Section~3, we explain our method in noise free case. We show the high precision of the quadratic (or parabola) approximation. We define the workspace (WS: relation between index range of a sample and a proper azimuth angle) and one-to-one correspondence between sample index and resonance angle. In Section~4, we try our method in a noisy environments. A curve-fitting procedure and three types of noise filters work to find satisfactory solutions. That is, in both 3. and 4., the resolution of the index is 7-digit usually, which is our target from the beginning. We think that the introduction of AI or statistical processing would increase the stability of the result. In Section~5, we mention some of future works. In APPENDIX A, we explain the method: How to find the azimuth angle, which we need in solving the diffraction problems by conically-mounted grating.
In recent years, surface magnetic resonance tomography (MRT), which is applied to the direct determination of the presence of groundwater, has been developed from underground two-dimensional to three-dimensional (3D) imaging. However, because of the influence of subsurface electrical conductivity, the magnetic resonance sounding (MRS) signal has been proved to be a complex-valued form. Moreover, the real and imaginary parts of MRS signals show different sensitivities to aquifers of different depths. In this study, a complex model of 3D MRT with separated loops configuration is introduced to provide accurate water-bearing imaging. Through simulation experiments, we demonstrate that the separated loops configuration is conducive to obtaining the imaginary part signal of MRS. Compared with a conventional model, the complex model has better 3D imaging resolution and sensitivity, especially for the deep regions. Moreover, in the case of noise interference and the presence of a multi-aquifer, the imaging results of complex inversion are reliable. As a result, this study is significant to the further development of multi-channel MRS instruments and provides a feasible method for high-precision imaging.
The objective of this paper is to propose an inversion model of soil moisture using a neural network, and compare the performance of this method with two empirical models in soil moisture inversion. A wide dataset of backscattering coefficients extracted from Sentinel-1 images and in situ soil surface parameter measurements (moisture content and roughness) are used. Since the available backscattering models have limited performances of describing the nonlinear relationship between soil parameters and backscatter coefficient, the retrieval of soil parameters from radar backscattering coefficient remains challenging. The proposed inversion method of a neural network is used for establishing this relationship. At the same time, two empirical models are employed to estimate the soil moisture for comparison. The results show that for most of the six measuring stations the inverted soil moisture with the neural network model has higher correlation coefficient with the in-situ soil moisture than those by the empirical models. Moreover, the neural network model inversion results under multi-polarization input conditions are discussed in this paper. The results of stations 2, 4, and 5 show that R2 of multi-polarization inputs are increased by 0.1928, 0.4821, and 0.2758 respectively, compared with those of single-polarization inputs.
In this paper, a reconfigurable patch antenna with Circular Polarization (CP) diversity with theoretical discussion and verification is proposed for the fifth generation (5G) of mobile communication systems. The proposed antenna contains two PIN diodes, which are correctly placed on the ground plane to attain polarization diversity. By switching between two ON/OFF modes in the PIN diodes, the proposed antenna can support the RHCP mode or the LHCP mode. An antenna with the well-matched impedance bandwidths (S11 ≤ -10 dB) of 2.5 GHz (27~29.5 GHz) and 3 GHz (36~39 GHz) and the dual-band 3-dB axial ratios of 6% (27.3-29 GHz) and 8.4% (35-38.2 GHz) operates at both the RHCP and LHCP modes. The experimental result shows that the proposed antenna has a circular polarization bandwidth at the center frequencies of 28 and 38 GHz for both the RHCP and LHCP.
In this paper, the thermal degradation of electro-conductive fabrics exposed to high current impulses is studied by using an equivalent resistive circuit and a technique commonly applied to the analysis of exploding wires. A method to estimate the threshold burst current of conductive fabrics is derived based on the so-called specific action, which is defined as the integral of the squared current density over the time applied at critical locations of the fabric such as the contact areas between yarns. The model has been experimentally validated on woven and non-woven fabrics using lightning impulse currents applied to the conductive fabrics coated with Cu-Ni alloy. A general rule for determining the dimensions of conductive fabrics as a function of the input-current specific-energy levels has also been derived.
In this paper, a wideband metasurface reflector that converts polarization of plane wave to the cross polarization with a double-square-shaped unit cell is presented, and the principle of polarization conversion based on polarization synthesis is also presented. The proposed structure has a unit cell with the longest dimension of 0.37 wavelength, a width of 0.23 wavelength, and a thickness of about 0.09 wavelength. 95% or more of the incident wave power is converted to cross-polarization covering a fractional bandwidth of 32.4% at 8.5 GHz.
A new class of the wideband series-fed microstrip array antenna is presented for X-band applications. A novel configuration of the reflector-slot-strip-foam-inverted patch (RSSIP) is proposed to provide high efficiency and wide operating frequency band. To improve the front to back ratio (FBR) and enhance the gain, a reflector is used. The series-fed configuration is selected for the array to simultaneously provide a very high efficiency and reduce the side lobe level. To experimentally verify the performance, a prototype of the array antenna is fabricated, and measurement is performed. This array consists of 12 sub-linear arrays with series-fed microstrip excitation. Also, each of these subarrays consists of 16 RSSIP antennas. An excellent agreement exists between measurement and simulation. The measured gain and efficiency of the fabricated antenna are 28.5 dB and 67% at 10 GHz, respectively. The measured impedance matching bandwidth (S11<-10 dB) is 24% which confirms the wideband characteristic of the antenna. The series-fed configuration results in very low measured SLL of -24.5dB at H-plane. The proposed 16 x 12 array antenna is a proper candidate for applications in MIMO systems and synthetic aperture radars (SAR).
The aim of this work is to discuss the possibility of resistive thin-film coatings used for vacuum electron devices. Following a short review, results on radiophysical parameters studies in millimeter-band of such coatings are presented. Resistive Sn-O coatings with varied oxygen content were fabricated on quartz substrates by reactive magnetron sputtering. Morphology and elemental composition of prepared coatings were studied by means of scanning electron microscopy and secondary ion mass spectrometry, while four-probe method was utilized to study the resistivity of those. Dielectric properties were measured in the V-band (50-70 GHz) in free space using vector network analyzer. It was demonstrated that resistivity and the dielectric properties of coating in millimeter-band can be widely varied by controlling coating composition.
This article presents a metamaterial-based microwave sensitive sensor with a complementary split-ring resonator (CSRR) structure for nondestructive surface crack detection in pipelines. The CSRR resonator is etched in the ground plane of a microstrip line and is produced using printed circuit board technology. The novelty of the proposed sensor is its structure that allows it to be directly used for nondestructive crack detection in pipelines, based on frequency and Q factor variations, even for cracks under a coating. A measurement setup was used to test the proposed sensor in pipelines of different materials: steel, PVC, and aluminum. The sensor could detect cracks of 1 mm. For a crack of 1 mm, the frequency shift was 6.10 MHz in steel, 2.62 MHz in polyvinyl chloride (PVC), and 1.70 MHz in aluminum. In some conditions, the Q-factor shift measurements were 6.72, 5.18, and 7.15 for steel, PVC, and aluminum, respectively. The proposed sensor features high sensitivity, small dimension, simple design, and easy fabrication.
A novel high-gain polarization reconfigurable antenna composed of a polarization conversion metasurface (PCM) and a linearly polarized source patch antenna is presented in this article. The PCM is placed above the source patch antenna with an air gap. The proposed PCM can convert the linear polarization (LP) wave radiated by the source patch antenna to LP wave, right-hand circular polarization (RHCP) wave and left-hand circular polarization (LHCP) wave by rotating the PCM around the center of the antenna. Meanwhile, the proposed PCM can serve as the partially reflective surface (PRS) of a Fabry-Perot (FP) resonant cavity which can achieve gain enhancement. In order to validate the performance of the proposed design, a prototype antenna is fabricated and measured. Simulated and measured results agree well. From 10.43 GHz to 11.2 GHz, the polarization reconfiguration can be achieved by rotating the PCM to different angles while maintaining the high gain performance simultaneously.