A compact microstrip rat-race coupler is proposed with a new phase inverter which is realized by a modified Lange coupling structure with a slotted ground plane and a floating-potential conductor. Based on the evenand odd-mode theory, its parameters are generally synthesized. In order to further miniaturize the rat-race coupler, a T-shaped line is utilized. A prototype operating at 2.0 GHz is designed and fabricated for verification. The circumference of our proposed rat-race coupler is only 0.52λ. Its in-phase and out-of-phase bandwidths are also enhanced, with reasonable agreement obtained between its simulated and measured S-parameters.
An antenna and an array with photonic bandgap (PBG) structures, which are cylindrical conformal microstrip antennas, both operating in X-band (10.2 GHz) are proposed. As shown in the simulation, PBG structures could suppress the surface wave propagating on substrate and balance the influence of cylindrical curvature at resonance frequency on antennas. The simulation results indicate that they have a higher gain and better directivity over the conventional antenna without PBG structure. Both of the antenna and the array are designed and manufactured, and the measurement results agree well with the simulations.
A compact dual band-notched ultra-wideband slot antenna with sharp band-notched characteristics and controllable notched bandwidths is presented. The antenna is formed by a rectangular slot with chamfered corners on a printed circuit board ground plane, a T-shaped stub and two sets of compound band-notched structures. The compound band-notched structures are employed to generate desired lower and upper rejected bands with satisfactory skirt characteristics and sufficient rejection bandwidths. Moreover, the bandwidth of either the lower or upper rejected band can be independently adjusted by changing the size and location of the corresponding band-notched structure. Finally, an UWB slot antenna with two rejected bands at WiMAX/WLAN frequencies is successfully simulated, designed, and measured, showing good impedance matching, stable gain and near omnidirectional radiation patterns.
The paper presents an analytical investigation of a tapered core optical fiber of which the outermost section is loaded with radially anisotropic liquid crystal. The analyses are dealt with transverse modes supported in the fiber structure followed by the relative distribution of power in the different fiber sections. Preliminary dispersion characteristics of the guide are also illustrated. The results demonstrate that the TE modes transport very large amount of power in the outermost liquid crystal region --- the criteria much useful for fiber optic sensing and field coupling devices.
The electromagnetic losses and shielding efficiency of shields for a buried three phase high voltage cable are studied for several shielding configurations. The shields are U-shaped gutters covered with plates, and the power cables are positioned either in trefoil or in flat configuration. The shielding efficiency and the losses are compared for shields with the same geometry but several shielding materials: aluminium, and two ferromagnetic steel grades. The numerical models are validated with experimental results. From the experiments, it is observed that the average reducing factor of the flux density is about 7 with the flat cable configuration while the average reducing factor of the flux density is about 5 with the trefoil cable configuration. But the power losses in the DX52 shield for trefoil configuration is about 40% lower compared to the flat configuration. In case of trefoil configuration, the losses are 12.41 W/m per meter length in the shield for a current of 750 A. Next to the shield material and the cable configuration, the paper investigates the influence of several parameters on both the shielding efficiency and the losses: the size of the shield, the current amplitude in the cable and the thickness of the shield.
In this paper, microstrip line resonators with loaded elements are proposed and studied to design microstrip diplexer. To demonstrate the design ideas, the equivalent circuits of the proposed resonators are built and studied. It is found that the different loads on different positions of the proposed half-wavelength resonator make the resonator have different features, which will easily control the characteristic of the diplexers. And here, resistor, open stub, and shorted stub are used as loaded elements. It is found the resistor loaded on the center of the microstrip line resonator can extremely reduce the unloaded quality factor of even-mode resonant frequency, which can be used to suppress the harmonics of the diplexer. The loaded open stub not only can reduce the size of the diplexer, but also can control the frequency ratio between the fundamental frequency and second harmonic of a resonator, which can increases the frequency ratio between the two passbands of the diplexer. As for the loaded shorted stub, it can enlarge the size of the diplexer. To demonstrate the design ideas, three diplexers are presented. The comparisons between the loaded and unloaded diplexers are given. The experimental results agree well to the theoretical predictions and simulations.
We present a rigorous full wave calculation of the optical force on a dielectric cylindrical particle of an arbitrary size under the illumination of one dimensional (1D) Airy beam. The radiation force is written in terms of the cylindrical partial wave expansion coefficients of the non-paraxial 1D Airy beams. Our simulation results demonstrate that an Airy beam can accelerate the microparticles along its parabolic trajectory, while transverse to which the particles are trapped at the center of its main lobe, corroborating the possibility of the long distance particle transport by means of an Airy beam.
Millimeter waves can be used to detect concealed objects because they can penetrate clothing. Therefore, millimeter wave imaging draws increasing attention in security applications for the detection of objects under clothing. In such applications, it is critical to estimate the distances from objects concealed in open spaces. In this paper, we develop a segmentation-based stereo-matching method based on passive millimeter wave imaging to estimate the longitudinal distance from a concealed object. In this method, the concealed object area is segmented and extracted by a k-means algorithm with splitting initialization, which provides an iterative solution for unsupervised learning. The distance from a concealed object is estimated on the basis of discrepancy between corresponding centers of the segmented objects in the image pair. The conventional stereo-matching equation is modied according to the scanning properties of the passive millimeter wave imaging system. We experimentally demonstrate that the proposed method can accurately estimate distances from concealed objects.
This paper presents the design, simulation and measurement of a dual-band terahertz metamaterial absorber with polarization-insensitivity and wide incident angle. The unit cell of the metamaterial consists of top resonator structures and low metallic ground plane, separated by an isolation material spacer to realize both electric and magnetic resonances. The physical mechanism of dual-band absorption and the sensitivity to the polarization direction and incident direction of the EM wave are theoretically investigated by simulating the x-component and normal component electric field distribution, current distribution on ERRs and metallic ground plane, and distribution of power flow and loss at the resonance frequencies as well as different modes EM waves, based the FDTD calculated method, respectively. The results show that the absorber is not only correctly coupling to the incident electric field and magnetic field, but also can trap the input power into specific positions of the devices and absorb it, besides insensitive to the polarized angle and incident angle. Moreover, the experiment demonstrates that the absorber achieves two strong absorptions of 82.8% and 86.8% near 1.724 and 3.557THz.
Recent studies on artificial materials demonstrate that substantial improvements in electromagnetic response can be attained by combining different materials subject to desired metrics. However, the perfect material combination is unique and extremely difficult to determine without automated synthesis schemes. In this paper, we develop a versatile approach to design the microstructure of periodic materials with prescribed dielectric and magnetic material tensors. The proposed framework is based on a robust material model and generalized inverse synthesis tool relying on topology optimization. The former is derived using homogenization theory and asymptotic expansion applied to Maxwell equations and can characterize the effects of anisotropy and loss of materials with periodic unit cells of arbitrary geometries and multi-phases much smaller than the wavelength. Resulting Partial Differential Equation (PDE) is solved numerically using Finite Element Analysis (FEA) and is validated with results in literature. The material model proves to be fast and numerically stable even with complex inclusions. The topology optimization problem is applied for the first time towards designing the unit cell topology of periodic electromagnetic materials from scratch with desired dielectric and magnetic tensors using off-the-shelf materials, i.e., readily available constituents obtained from isotropic ceramic powders. The proposed framework's capability is demonstrated with five design examples. Design with anisotropic permittivity is also fabricated. Results show that the framework is capable of designing, in an automated fashion, non-intuitive material compositions from scratch with desired electromagnetic properties.
The berthing of large ships in inclement weather with frequently poor visibility presents a challenge. To assist with this application, it may be beneficial to utilise standard radar imaging. Whilst this may be achieved using a mechanically-scanned system, reliability, cost and weight issues, coupled with the need to primarily image only a 120º sector on the port and starboard of the ship, make phased array radar an attractive possibility. Multiple-Input Multiple-Output (MIMO) radar, with its ability to enhance the resolution available from a given number of elements, is particularly suited to a short-range application such as this in which there is sufficient time to switch between antenna elements as an alternative to more complex implementations. This paper describes a system of this nature from its basic architecture to development and validation, including some artefacts of the particular topology employed.
The magnetic properties of the metamaterial composed of both periodic and aperiodic closed rings are studied. Experimental results validate that metamaterials with 0 < μ < 1 can be non-dispersive in a wide frequency range. The magnetic properties are insensitive to disorders of the closed rings, e.g., the position disorders and the size disorders. The related causality issue is also discussed.
This paper presents a method for extracting the coupling matrix and the unloaded Q from the measured (or electromagnetic simulated) S-parameters of a narrow band cross-coupled resonator bandpass filter with losses. The Cauchy method is applied to determine the characteristic polynomials of the S-parameters of a filter in the normalized low-pass frequency domain. A five-parameter optimization method is proposed to obtain the unloaded Q and remove the phase shift of the measured S-parameters, which is caused by the phase loading and the transmission lines at the input/output ports of a filter. Once the characteristic polynomials of the S-parameters with the phase shift removed have been determined, the coupling matrix of a filter with a given topology can be extracted using well established techniques. Two application examples are given to illustrate the validity of the proposed method.
The design and measured results of a compact, low cost, low conversion loss microstrip single balanced Schottky diodes mixer is proposed. This mixer is designed for Ka-band satellite transponder simulator to convert the 30 GHz radio-frequency (RF) signal down to the 20 GHz intermediate-frequency (IF) signal with 9.8 GHz local oscillator (LO) frequency. This design takes full advantage of the frequency relationship of the RF, IF and LO, which is 3 : 2 : 1. A microstrip rat-race ring is designed at the LO frequency, which also functions as a 180-degree hybrid coupler at the RF frequency by its intrinsic multi-band characteristic. The amplitude and phase balance at both LO and RF frequency are analyzed, which guarantee the state-of-art performance of this single balanced mixer. The multi-function open/short stubs and a lowpass filter (LPF) with bonding wires across the rat-race ring are optimized to realize this low conversion loss mixer. The measured results show that the conversion loss is less than 9 dB at the IF frequency from 20.0 to 21.6 GHz, and the power of the second harmonic of LO is -45dBm with +6.5dBm LO drive power. The 3rd order inter-modulation products (IMD3) could be lower than -50 dBc with LO power higher than +7.8dBm at the input RF power of -15 dBm.
A set of characteristic basis functions of the energy radiation pattern for a true-time-delay array of equi-spaced elements radiating a pulsed/transient wave-field was derived. This set is determined by the array layout and by the set of excitation waveforms that can be used to expand the actual excitation pulse. It is established that the characteristic basis function set spans the mapping of the square amplitudes of the discrete Fourier transform of the excitation coefficients to the energy radiation pattern. This mapping is further used to analyze array performance and re-examine the term array sparsity. Additional use of this set can be found in synthesizing an array radiation pattern to meet prescribed requirements.
The propagation characteristics of electromagnetic waves at the interface between an isotropic regular medium and an anisotropic metamaterial for arbitrary orientation of principal axis are investigated. In terms of the different sign combinations of the tensor components along principal axes, the anisotropic media are divided into four classes. The existence conditions of negative refraction are discussed in different cases, indicating that the conditions for the existence of negative refraction are closely dependent on the principal components and the rotation angle. Furthermore, the influence of the rotation of the principal axes on the incident angle region is analyzed for each case, and the optimal material parameters are attained for the maximum area of the incident angle region of negative refraction occurrence.
Electrothermal effects in various through silicon via (TSV) arrays are investigated in this paper. An equivalent lumped-element circuit model of a TSV pair is derived. The temperature-dependent TSV capacitance, silicon substrate capacitance and conductance are examined for low-, medium-, and high-resistivity silicon substrates, respectively. The partial-element equivalent-circuit (PEEC) method is employed for calculating per-unit-length (p.u.l.) resistance, inductance, insertion loss and characteristic impedances of copper and polycrystalline silicon (poly-Si) TSV arrays, and their frequency- and temperature-dependent characteristics are treated rigorously. The modified time-domain finite-element method (TD-FEM), in the presence of a set of periodic differential-mode voltage pulses, is also employed for studying transient electrothermal responses of 4- and 5-TSV arrays made of different materials, with their maximum temperatures and thermal crosstalk characterized thoroughly.
The symmetric and asymmetric double Langmuir probe systems with their necessary driving circuits are developed for characterization of low pressure inductively coupled nitrogen plasma, generated and sustained with 13.56 MHz RF source and an automatic impedance matching network. First of all the plasma parameters such as ion saturation current, electron temperature and electron number density are determined with symmetric double probe system at different input RF powers, filling gas pressures and radial distance from the plasma chamber wall. Then the electron temperature and electron energy probability function are determined with asymmetric double probe system at the centre of the discharge plasma chamber by changing the filling gas pressure and input RF power. It is observed that the electron temperature and electron number density increase with the increase in input RF power and radial distance but decreases with the increase in filling gas pressure. The electron energy probability function determined with asymmetric probe system evidently deviates from the Maxwellian, particularly at low filling gas pressures.
A novel approach to moving target detection is proposed for dual-channel SAR system. This approach is on the basis of eigen-decomposition of the sample covariance matrix and examines the statistic of the second eigenvalue and the Along-Track Interferometric (ATI) phase for ground moving target indication. Based on this statistic, a new Constant False Alarm Rate (CFAR) detector can be designed to solve the problem of GMTI. To detect slow moving targets more accurately, the second eigenvalue and the ATI phase pre-thresholds are implemented before a CFAR detector. Experimental results on measured SAR data are presented to demonstrate that this novel detector has wider range of detection velocity and lower false alarm probability.
To deal with pattern synthesis of antenna arrays, a chaotic particle swarm optimization (CPSO) is presented to avoid the premature convergence. By fusing with the ergodic and stochastic chaos, the novel algorithm explores the global optimum with the comprehensive learning strategy. The chaotic searching region can be adjusted adaptively. To evaluate the performance of CPSO, several representative benchmark functions are minimized using various optimization algorithms. Numerical results demonstrate that the proposed approach improves the performance of the algorithm significantly, in terms of both the convergence speed and exploration ability. Moreover, CPSO was applied to array synthesis examples, including the equally spaced linear array, unequally spaced linear array and conformal array, compared with other optimization methods. Experimental results show its high performance in the pattern synthesis with low side lobe, multi-nulls and shaped beam.
A novel microstrip quad-band bandpass filter was designed and fabricated on an Al2O3 ceramic substrate of 1 mm thick. Two different types of open-loop resonator --- a winding line-shaped resonator (WLR) and a stepped impedance resonator (SIR) --- were positioned in parallel at the two sides of input/output microstrip lines that had the same coupling lengths and coupling gap widths. The proposed filter was based on a WLR with four different resonant frequencies: 1.23 GHz, 2.49 GHz, 3.73 GHz, and 5.41 GHz. By carefully selecting the resonant frequencies of the two resonators to be slightly different, the phase difference for the signals in the two resonators was negative, indicating that energy cancellation occurred, resulting in wide bandwidths and deep transmission zeros. The spurious resonant frequencies of the SIR were designed to be non-integer multiples of the fundamental resonant frequency by adjusting the length, characteristic impedance ratio, and electrical length. The SIR was designed to have three resonant frequencies at around 2.27 GHz, 3.37 GHz, and 4.94 GHz, which had phase differences with the WLR's resonant frequencies of 2.49 GHz, 3.73 GHz, and 5.41 GHz. Finally, a novel quad-band filter with a narrow band in the L2-band (GPS, 1.227 GHz) and three wide bands in the WIMAX (3.5 GHz) and WLAN (2.4 GHz and 5.2 GHz) was achieved.
Organic-inorganic thermoplastic composites offer a cost-effective material choice with tuneable dielectric properties for various telecom components and applications. Typically such composites require substantial loading of inorganics to obtain a feasible level of permittivity at RF frequencies dramatically decreasing mechanical ruggedness and increasing losses. In this paper we demonstrate utilization of nanoparticle phase in BaSrTiO3-polypropylene-graft-poly (styrene-stat-divenylbenzene) composite to enhance the high frequency properties and overcome the problems associated with high filler loading. The effect of nanosize silicon, silver and Al2O3 additives with different volume fractions in complex permittivity was investigated up to 1 GHz. Significant increase in the effective permittivity of the composites with all the additives was observe, especially in the case of the nanosized silver particles where only 2 vol.% addition was able to enhance εr by 52% without increasing the dielectric losses when compared to the reference sample.
In this paper, an improved CBFM/p-FFT algorithm is presented, which can be applied to solve electromagnetic scattering problems of large-scale periodic composite metallic/dielectric arrays, even when the array has electrically small periodicity or separating distance. Using characteristic basis function method (CBFM), scattering characteristics of any inhomogeneous targets can be represented by special responses derived from a set of incident plane waves (PWs). In order to reserve the dominant scattering characteristics of the targets and remove the redundancy of the overfull responses, a singular value decomposition (SVD) procedure is applied, then, new series of basis functions are built based on the left singular vectors after SVD whose corresponding singular values beyond a predefined threshold. However, the algorithm of CBFM combined with method of moments (MoM) still requires a lot of memory and CPU resources to some large scale problems, so the precorrected-fast Fourier transform (p-FFT) method is applied based on the novel built basis functions, with which, the required memory and solve time for solution can be reduced in an extraordinary extent. For a near correction technique is applied to process the interactions between cells placed within a distance less than a predefined near-far field threshold, arrays with electrically small periodicity can be analyzed accurately. Moreover, the incomplete LU factorization with thresholding (ILUT) preconditioner is applied to improve the condition number of the combined algorithm, which improves the convergence speed greatly.
This paper presents a new method of sequential microwave filter tuning. For filters with R tuning elements (including cavities, couplings and cross-couplings), based on physically measured scattering characteristics in the frequency domain, the Artificial Neural Network (ANN) is used to build inverse models of R sub-filters. Each sub-filter is associated to one tuning element. The sub-filters are obtained by successive opening or shorting of resonators and by removing coupling screws. For each sub-filter, the ANN training vectors are defined as physical reflection characteristics (input vectors) and the corresponding positions of the tuning element, which is detuned, in both directions, from its proper setting (output vectors). In the tuning process, such inverse models are used for calculating the tuning element increments needed for setting the tuning element in the proper position. The tuning experiment, conducted on 8- and 11- cavity filters, has shown the performance of the presented method.
Synchronization performance of a pulse-based ultra-wideband (UWB) system is investigated by taking into account of distortions caused by transmitter and receiver antennas and wireless propagation channels in different environments. The synchronization scheme under consideration can be achieved in two steps: a slide correlator and a phase-locked loop (PLL)-like fine tuning loop. Effects of the non-idealities are evaluated by analyzing the distortion of the received UWB pulse and subsequently the synchronization performance of the pulse-based UWB system. It is found that generally a smaller step is required for the sliding correlator due to distortions introduced by the antennas and channels. However, the fine tuning loop can always be stabilized by adjusting the loop parameters. Therefore, synchronization can always be achieved.
In this paper two four-pole filters at X-band are presented, both designs use a coaxial quarter wavelength resonator suspended in air by short circuits between the coaxial center and outer conductor. Different couplings between suspended resonators have been used to obtain a Chebyshev and a quasi-elliptic response. The Chebyshev filter was designed to have a 9.2 GHz centre frequency with a 4% fractional bandwidth. The second design is a quasi-elliptic filter composed of two vertically stacked rectangular coaxial lines, where one pair of resonators is placed on the lower coaxial line and another pair is located on the upper line. Coupling between coaxial lines is achieved through an iris in the common coaxial ground plane. The quasi-elliptic filter has been designed to have a centre frequency of 9.1 GHz with a 4% fractional bandwidth. Two transmission zeros located at the sides of the passband have been successfully achieved with the proposed filter topology. Experimental results for both designs are presented, where a good agreement with simulations has been obtained.
In this paper, the characteristics of three different types of high impedance surfaces (HIS) to be used as ground planes for low profile wire antennas are investigated and compared: a mushroom-like surface, which is the classical example of HIS with connecting vias, and two surfaces with no vias, one of which is anisotropic. Both the simulation results and the measurements verify that the high impedance behaviour is successfully accomplished around the resonant frequency. In order to complete the study, return loss and radiation pattern of a horizontal dipole placed above the surfaces are analyzed.
Image preprocessing is commonly used in infrared (IR) small target detection to suppress background clutter and enhance target signature. To evaluate the performance of preprocessing algorithms, two performance metrics, namely PFTN (potential false targets number) decline ratio and BRI (background relative intensity) decline ratio are developed in this paper. The proposed metrics evaluate the performance of given preprocessing algorithm by comparing the qualities of input and output images. The new performance metrics are based on the theories of PFTN and BRI, which describe the quality of IR small target image, by representing the difficulty degree of target detection. Theoretical analysis and experimental results show that the proposed performance metrics can accurately reflect the effect of the image preprocessing stage on reducing false alarms and target shielding. Compared to the traditional metrics, such as signal-to-noise ratio gain and background suppression factor, the new ones are more intuitive and valid.
The kinematic properties of an array of transmitting antennas that are transiently excited by a sequence of modulated pulses, with high repetition rate, are explored. The array's parameterization is carried out via the energy radiation pattern. It is shown that the energy radiation pattern can be decomposed into a set of different types of beam contributions, defined over a beamskeleton, which is determined by the array's physical and excitation parameters. The different types of beams are main beams, gratinglobe beams and cross-pulsed lobe beams, each corresponding to a different pulsed interference mechanism. While grating lobes are timeharmonic phenomena, cross-pulsed lobes are unique for excitation with a pulsed sequence. The different beam types set limits for array sparsity in terms of the array's physical and excitation parameters. The array's directivity is introduced as a figure of merit of its performance and to demonstrate the resulting effect of the time-domain excitation characteristics. The array's parameterization can be used with any type of excitation --- from extreme narrow band (time-harmonic) to extreme ultra-wideband (transient/short pulsed) excitation. For timeharmonic excitation, the resulting characterization matches that of the classical frequency domain antenna theory.
In the field of High Frequency Surface Wave Radar (HFSWR), this paper deals with a study which determines the electric permittivity and conductivity values that a medium must hold to propagate a sole surface wave at its interface with air. Firstly, we demonstrate clearly the reason why the Zenneck Wave cannot be excited on sea surface. Kistovich decomposition is used for this purpose. Secondly, the reasoning is extended to identify electric permittivity and conductivity values that permit to excite a surface wave on an homogeneous medium. Finally, numerical validation is obtained by comparison with the analytic formulation of the field radiated by a vertical Hertzian dipole as it has been established by Norton.