A broadband gradient index (GRIN) metamaterial lens for gain enhancement of circularly polarized antennas has been automatically designed, fabricated and investigated. The GRIN metamaterial lens consists of an isotropic dielectric plate with a corresponding distribution of deep-subwavelength drill holes each with the same diameter. Such drill holes have a negligible influence on both the polarization state and the spectral response of the electromagnetic wave transmitting through the resulting GRIN metamaterial lens. Therefore, the GRIN metamaterial lens is polarization-insensitive and can efficiently transform spherical waves into planar waves over a very broad frequency range keeping the initial polarization states (e.g. linear or circular) scarcely changed. In the following we have derived analytical formulas that enable the setup of distribution rules for the drill holes on the plate. Based on these formulas, the GRIN metamaterial lens can be automatically designed and easily fabricated using circuit board engraving machines. The proposed GRIN metamaterial lens has been tested by placing it on the aperture of a circularly polarized conical horn antenna. The agreement between simulation and measurement results shows that the gain of the horn antenna has been significantly increased within the whole X-band (i.e. from 8 GHz to 12 GHz) and the largest gain enhancement reaches up to 5.7 dB. In particular, the axial ratio of the horn antenna with the GRIN metamaterial lens is less than 1.6 dB.

Pipelines made of dielectric materials such as Polyethylene (PE) are becoming increasingly popular. With no suitable inspection technique for dielectric pipes, there is an urgent need to develop new technology for their inspection. This paper presents a novel pipe inspection technique using Electrical Capacitance Tomography (ECT) imaging. Traditionally ECT is used for industrial process tomography as a low resolution but fast tomographic imaging technique. Typically commercial ECT can provide a resolution of approximately 10 percent of the imaging region. In this paper a limited region tomography technique is developed take into account prior knowledge about the geometry of the pipe. This has signicantly enhanced the imaging resolution of the ECT system, making it a viable pipe inspection solution. The experimental results in this study demonstrate an interior wall loss area as small as 0.195 percent of the ECT cross sectional imaging region is repeatable and can be reliably detected. A narrowband pass filter method (NPFM) is used as a means to limit the region for the ECT algorithm. This results in an unprecedented resolution, making ECT a viable non-destructive evaluation (NDE) technique for plastic pipes. The NDE application of the ECT for PE pipes is demonstrated in this paper with several experimental results. A wall loss of depth of 1.5 mm could be detected for an ECT sensor array of 150 mm in diameter, showing a high resolution and high definition ECT (HD-ECT) imaging that has not been reported before.

The model based on range and Doppler equations (RD model) is the most precise model for SAR geolocation, and therefore SAR geolocation based on this RD model has become more and more popular. Unfortunately, the RD method requires iterative solution, in most case, which is time-consuming and prone to poor optimization due to observation errors of parameters. In face of the huge mass of measured data from global SAR measurements, how to improve processing speed while maintaining geolocation accuracy is an important problem. This paper examines how to solve the RD geolocation equations for single, interferometric, and stereo SAR. First, the RD geolocation equations for the three kinds of systems are abstracted into a unified equation form. Second, it is determined that the RD geolocation equation can be approximated as a mapping relationship using polynomials. Then a fast solution method for the unified geolocation equation is proposed based on the Range Doppler Polynomial Coefficient Model (RDPC). Third, the accuracy loss of the RDPC model is analyzed, and the precision differences among the three kinds of system are compared. Finally, several groups of TerraSAR-X measured data for the three modes are processed using the fast algorithm. The results show that the fast algorithm greatly reduces the amount of calculation while the geolocation accuracy loss is small. Performance evaluation demonstrates that the proposed method is efficient and correct.

A new design methodology for multi-band rectangular microstrip antenna using a metamaterial-inspired technique is proposed. The methodology uses the metal disk with SRR-shaped slot placed horizontally between the patch and the ground plane. With the introduction of the split ring, sub-wavelength resonance can be achieved while the dominant mode of patch cavity remains the same, so the antenna can operate at multi resonant frequencies. Construction of the multi-band antenna requires only the sandwiching of two etched circuit boards. The antenna has the properties of low profile, easy fabrication and low cost. Dual-band and tri-band antennas are fabricated and measured, which validate the design methodology.

Composites of rice husks and carbon nanotubes (RHCNTs) are an innovation in improving the absorption of microwave signals. Rice husks, which are an agricultural waste material, have been found to possess a significant propensity for absorbing microwave signals. Studies have shown that both rice husks and carbon nanotubes (CNTs)have high percentages of carbon. Thus, in this paper, we present the results of our experimental study in which we varied the ratios of rice husks and CNTs in the composite materials and determined the dielectric properties of the composites and measured their abilities to absorb microwave signals. The experimental microwave absorber was fabricated using rice husks and CNTs, which increased the dielectric constant and the loss factor.Complex permittivity was measured using an Agilent dielectric probe.The RHCNT compositeswere investigated to determine their reflection loss and absorption performance as microwave absorbers. For the fabricated microwave absorber,we used the rectangular waveguide measurement technique to study reflection loss, transmission loss, and absorption performance in the frequency range of12.4 - 18 GHz. Carbon has an essential role in the absorber due to its ability reflect/absorb microwave signals.Thus, we compared the abilities of a pure rice-husk (PRH) absorber and RHCNT composites absorbers to absorb microwave signals.

In this work, a subharmonic frequency mixer for millimeter wave applications has been designed. The mixing and multiplication phenomena are simultaneously achieved via a nonlinear component consisting in a microstrip line gap covered by a graphene film coating. The circuit structure is made up of various filters, which have been optimized to ensure high port-to-port isolation. The nonlinear behavior of the subharmonic frequency mixer has been experimentally evaluated within the 39-40.5 GHz RF frequency band. The frequency downconversion is achieved by mixing the RF signal with the second harmonic component of a 17.9 GHz LO signal. Conversion losses are minimized by generating a return path for IF, through the use of a quarter wavelength open-ended stub.

A new broadband multiple-input multiple-output (MIMO) antenna with good isolation and compact size is proposed. The proposed antenna consists of two G-shaped elements in the upper layer and two inverted L protrude branches and a T slot etched in ground which is used to reduce the mutual coupling. This planar antenna has a bandwidth of 100% with |S₁₁| ≤ -10 dB from 2.26 to 6.78 GHz. The value of isolation between the two antenna elements is more than 22.5 dB in the whole band. The experimental results verify the simulations.

For ultra-wideband synthetic aperture radar (UWB SAR), there often exist a lot of clutters in the image, and the weak targets are easy to be masked by them. However, using the prior scattering knowledge of targets, enhanced imaging can be realized and beneficial improvements in image quality and detection performance can be expected. In this paper, an enhanced imaging method for body of revolution (BOR) has been researched. Since the BOR target has the unique feature of aspect-invariant characteristic, the aspect scattering entropy (ASE) is proposed to describe the diversity of aspect scattering and used in the BOR-enhanced imaging method. Then the application of the proposed method in landmine detection is discussed. The experimental results show that the BOR targets are effectively enhanced and the clutters are surpressed and thus the probability of landmine detection increases under the same false alarm rate.

In monostatic radars systems, only the micromotion signatures projected onto the radar line-of-sight (LOS) can be observed from echoes. As a result, the obtained micromotion signatures (e.g., the radius length of rotation) are sensitive to the radar LOS. In this paper, we propose a method for the accurate estimation of three-dimensional (3-D) micromotion signature with the orthogonal frequency division multiplexing - linear frequency modulation (OFDM-LFM) multi-input multi-output (MIMO) radar technique, which makes use of the advantages of the multi-view of MIMO radar systems and the broad bandwidth of the OFDM-LFM signals. In the proposed method, the Hough transform and Orthogonal Matching Pursuit (OMP) algorithm are introduced to extract the m-D curve features from echoes, and then the 3-D micromotion signatures of the rotating targets are obtained by solving nonlinear multivariable equation systems. The extracted 3-D micromotion signatures are no longer sensitive to the radar LOS, and can provide realistic feature information for target recognition. Simulations are given to validate the effectiveness of the proposed method.

A probe-compensated near-field - far-field (NF-FF) transformation with spherical spiral scanning, which makes possible to lower the number of needed measurements, as well as the time required for the data acquisition when characterizing quasi-planar antennas, is experimentally verified in this paper. Such a technique, based on the nonredundant representation of electromagnetic fields, has been achieved by properly applying the unified theory of spiral scans for nonspherical antennas and adopting a very flexible source modelling, formed by two circular "bowls" with the same aperture diameter but different bending radii. A two-dimensional optimal sampling interpolation formula allows one to reconstruct the NF data at any point on the measurement sphere and, in particular, at those required by the classical NF-FF transformation with spherical scanning. The reported NF and FF reconstructions, obtained from the nonredundant samples acquired on the spiral, assess the accuracy of the proposed technique.

The ship Kelvin-wake models on two-dimensional (2-D) linear and nonlinear sea surfaces are combined with the second-order small-slope approximation method (SSA-II) to comparatively study the corresponding electromagnetic (EM) scattering characteristics. The nonlinear sea-surface models include the Choppy Wave Model (CWM) and the second-order Creamer model (Creamer (2)). Considering the limitations of using the ideal plane EM wave incident upon a rough sea surface of the limited size, the expressions of the scattered field and scattering amplitude are derived by utilizing the modified tapered incident field. Due to the fact that the nonlinear effects of Creamer (2) surfaces is obviously stronger than those of CWM surfaces, the bistatic normalized radar cross section (NRCS) calculated from Creamer (2) surfaces is significantly greater than that of its linear and CWM surfaces for scattering angles departing from the specular direction, and the backscattering coefficients from Creamer (2) surfaces are also the greatest except within quasi-specular (near vertical incidence) region. In addition, for the linear and nonlinear sea surfaces, the influences of different wind speeds and directions on scattering characteristics are also calculated and analyzed in detail. However, taking the ship Kelvin wakes into account, the corresponding scattering features are obviously distinct from those of the single linear and nonlinear sea surfaces. This helps to provide a basis to extract the related ship information through the scattering characteristics of ship Kelvin wakes. Also it shows that the small-slope approximation method is a very effective analysis method to deal with the EM scattering from the rough sea surface.

Computer keyboards are often used to transmit confidential data such as passwords. The sensitive information such as keystrokes could be recovered by using the electromagnetic (EM) waves from the electronic components of the keyboard. In this paper, we have investigated the information leakage on the ground line of the PS/2 serial cable due to crosstalk and radiative coupling. The coupling principles are analyzed firstly. And then, through the experiments we found that the signals of keystrokes could leak to the ground line network which could then be detected on the other power outlets whose share the same electric line. Lastly, the eavesdropping experiments demonstrated that the keystrokes could be reproduced on the other places of the ground line network with no trace.

In this paper, an ultra wideband antenna employing a defected ground structure is presented. The radiating element is a circular patch on which a fractal based geometry is inscribed in the form of slots and excited by a tapered feed-line for impedance matching. The antenna has an impedance bandwidth of 8.2 GHz (117% at centre frequency of 7 GHz) and a peak gain around 6 dB. To improve the impedance bandwidth and gain, a Swastika shape Electromagnetic band gap (EBG) structure is proposed. The unit cell of the proposed EBG has a compact size of 3 mm × 3 mm and is obtained by introducing discontinuities in the outer ring of the Cross-Hair type EBG. The stop band (-20 dB) achieved with this EBG is 3.6 GHz (7.5 GHz-11.1 GHz) which is 1.6 GHz more than that achieved by a standard mushroom-type EBG of the same size and same number of elements. After application of the proposed EBG, there is an improvement of 12% in the impedance bandwidth while the peak gain increases by about 2-3 dB. The radiation of the antenna shows a dumb-bell shaped pattern in the E-plane and Omni-directional pattern in the H-plane. All the measured results are in good agreement with simulated results.

The combined method to investigate the electron spectrum of single n-type d-doped quantum wells in silicon is proposed. It is based on computing the electron potential energy by means of the Thomas-Fermi method at finite temperatures; then the obtained electron potential energy is applied to the iteration procedure with solving the Schrodinger equations for the electron spectrum and the Poisson one for the potential energy. The many-body corrections to the electron spectrum in the quantum well also have been investigated. The combined method demonstrates a rapid convergence. It is shown that that the simple TF method gives a good approximation for the electron potential energy and for the total electron concentration within the well.

In this paper, fusing of a metallic conductor is studied by judiciously using the solution of the one-dimensional heat equation, resulting in an approximate method for determining the threshold fusing current. The action is defined as an integration of the square of the wire current over time. The burst action (the action required to completely vaporize the material) for an exploding wire is then used to estimate the typical wire gapping action (involving wire fusing), from which gapping time can be estimated for a gapping current greater than a factor of two over the fusing current. The test data are used to determine the gapped length as a function of gapping current and to show, for a limited range, that the gapped length is inversely proportional to gapping time. The gapping length can be used as a signature of the fault current level in microelectronic circuits.

In this paper, the difference scheme of the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is replaced by the quasi isotropic (QI) spatial difference scheme to improve its numerical dispersion characteristics. The unconditional stability advantage of QI-ADI-FDTD is analytically proven and numerically verified. The numerical dispersion of the novel method can be dramatically reduced by choosing proper weighting factor. An example is simulated to demonstrate the accuracy and efficiency of the proposed method.

A subspace self-calibration ESPRIT algorithm for mutual coupling across an electromagnetic vector sensor is proposed in this paper. By introducing an auxiliary array element, the mutual coupling is calibrated. The whole array's mutual coupling matrix can be obtained simultaneously. A mathematic model for mutual coupling across the six collocated antennas of an electromagnetic vector sensor is established. And the solution of mutual coupling matrix was transformed into the solution of several matrix elements. The Cramer-Rao Lower Bound (CRLB) is also derived in the end of this paper to verify the efficacy of the proposed algorithm. The simulation results demonstrate that this approach is correct and effective.

In the framework of wide-band and ultra wide-band array antennas, an Optical Time Steered Antenna (OTSA) is presented, by considering the design strategies of a new True Time Delay (TTD) Control Unit in the Beam Forming Network (BFN). The unit has high reliability, low crosstalk, low switching time and potential low cost, being based on a low cost technology. Furthermore, due to its compactness and modularity, it can be easily grouped with other ones to make a control unit of large arrays. Different strategies and working configurations of the TTD control unit are presented as a trade-off among hardware complexity, insertion loss reduction and beam control capability. The design of an OTSA prototype is discussed by considering a realistic model simulating the behavior of a real world antenna and accounting for unavoidable non-realities, such as random, periodic and systematic errors introduced by each device exploited in the OTSA as well as mutual coupling between radiating elements. An optimal trimming strategy, able to compensate at best for BFN errors and based on the use of suitably located trimmers, is presented. Among other cases, to enlighten the potentialities of the OTSA, an all optical architecture providing a difference beam squint free pattern is also proposed.

This paper presents two novel dual-mode dual-band bandpass filters (BPFs) by using stubs loaded coupled line. The analytical equations of their transmission poles and transmission ze-ros are given by the classical even-/odd-mode method. Design rules for two dual-band BPFs are al-so given, which shows the easily tuned passband frequency locations and in-band performance. As examples, two dual-mode dual-band BPFs, dual-band filter A with central frequencies (CFs) at 3.5/6.8 GHz and -3 dB fractional bandwidth (FBW) of 14%/10%, while dual-band filter B with CFs at 2.4/6.8 GHz and -3 dB FBW of 43%/16% are designed, fabricated and measured. Good agree-ment can be observed between the simulations and measurements. These two filters exhibit simple design procedures, simple physical topology, low insertion losses, good return losses, high isolation and compact sizes.

A compact quadrature hybrid coupler with harmonic suppression adopting lumped-element band-stop resonator is proposed aiming for bandwidth improvement. Conventionally, harmonic rejection is realized by three band-stop resonators in lumped hybrid design. The using of three band-stop resonators can realize better harmonic suppression while exhibiting narrower frequency response. So as to improve operation bandwidth performance, the number of band-stop resonator applied in this proposed topology is minimized to one. Trading off with acceptable reduction in harmonic rejection, the proposed hybrid can enlarge working bandwidth with fewer lumped devices. Detailed design and theoretical analysis are presented and the expressions of lumped elements with dependence of rejected harmonic frequency are obtained. To validate the analysis, three 2.45 GHz couplers are fabricated on an FR-4 printed circuit board. The experimental results exhibit 27.3%, 26.9% and 23.3% operation bandwidth with better than 16 dB, 17 dB, and 21 dB harmonic suppressions at 4.9 GHz, 6.1 GHz, and 7.35 GHz, respectively. Less than 0.8 dB amplitude imbalance and 2° phase error are achieved over the whole operation frequency for the all three couplers, which are matched well with theoretical analysis.