A compact multiband omnidirectional antenna for the reception of GNSS signals on artillery projectiles is designed in this paper. The proposed antenna consists of a metallic cone comprising a T-shaped monopole. It exhibits a broad bandwidth from 1.22 GHz to 1.28 GHz and from 1.44 GHz to 1.75 GHz, covering GPS L1, Galileo E2-L1-E1, GLONASS G1 and G2, CNSS B1 and B3. Measured results show that an omnidirectional radiation pattern is achieved, and the non-circularity in the azimuthal plane (xy-plane) is less than 2 dB for all the desired bands. Then the measured 6 dB beamwidth is about 110° in the presence of a finite 20 millimeters (mm) radius ground plane. Such an antenna has the potential to be easily used for small artillery projectiles.

This paper presents an alternate microwave imaging system that greatly reduces design and operation complexities compared to traditional imaging systems. At the heart of this novel system lies an electronically reconfigurable beam-scanning reflectarray antenna. The high tuning capability of the reflectarray provides us a broad steering range of ±60˚. The beam is steered across this range and the scattered field is recorded. The collected data are used for image reconstruction by means of the time reversal signal processing technique. Experimental results of the detection of various dielectric targets are presented.

A circular microstrip patch antenna design is proposed for applications that require suppression of surface waves and lateral waves. The proposed design is composed of a circular patch loaded with a single shorting pin on a grounded inhomogeneous dielectric substrate with a desired effective permittivity. The modal equation for the normalized resonance frequency of this design is solved numerically. Simulated and measured radiation patterns show that a good reduction of surface waves and lateral waves is achieved. A comparison between the present work and an alternative design in the literature is presented in this paper. The proposed design could find applications in large patch antenna arrays where mutual coupling needs to be eliminated and in high-precision global positioning system receivers where multipath interfering signals associated with low-angle reflection affect position accuracy.

A new compact microstrip ultra-wideband (UWB) bandpass filter (BPF) with improved out-of-band rejection and good selectivity is proposed using a modified ring multiple-mode resonator (MMR). The initial UWB bandpass filter comprises interdigital coupled lines and a conventional ring MMR. Then, four high-low impedance resonant cells are periodically placed in the inner area of the conventional ring MMR, which have the properties of achieving harmonic suppression and size reduction. To validate the design theory, a new compact microstrip UWB BPF with improved out-of-band rejection is designed and fabricated. Both simulated and experimental results are provided with good agreement.

A worst-case tolerance synthesis problem for low-sidelobe sparse linear arrays is solved by using a novel self-adaptive hybrid differential evolution (SAHDE) algorithm. First, we establish a worst-case tolerance synthesis model for low-sidelobe sparse linear arrays, in which random position errors are considered and assumed to obey the Gaussian distributions. Through the random sampling, the random model is converted to a deterministic optimization problem. Then, a novel SAHDE algorithm is presented for solving the problem. As a modification to the existing hybrid differential evolution algorithm, a simplified quadratic interpolation (SQI) operator is used to tune the control parameters self-adaptively, establishing the connections between control parameters and the fitness values. In order to determine appropriate control parameter values quickly, a selection operation is also used. Detailed implementation procedure for the SAHDE algorithm is presented, and some numerical results show its effectiveness. Finally, for the deterministic optimization problem, we present a fast way for calculating its fitness values. The SAHDE algorithm is used to obtain optimal nominal element positions. Simulated results illustrate that the worst-case peak sidelobe levels for the sparse linear arrays are improved evidently. The SAHDE algorithm is efficient for solving the worst-case tolerance synthesis problem.

In this paper, a compact multiple-input-multiple-output (MIMO) antenna is proposed for ultra wideband (UWB) communication. The UWB MIMO antenna consists of two identical monopole antenna elements with a comb-line structure on the ground plane to improve impedance matching and enhance isolation. Simulation and measurement have been analysed in terms of reflection coefficient, mutual coupling, dispersion diagram, radiation pattern, peak gain, efficiencyand envelope correlation coefficient. Results show that the antenna has an impedance bandwidth larger than 3.1-10.6 GHz, mutual coupling between the two ports lower than -25 dB and envelope correlation coefficient less than 0.001 across the UWB band. The proposed antenna has a compact size of 26×31 mm². All the measured and calculated results show that the proposed UWB MIMO antenna is a good candidate for UWB MIMO systems.

The rigorous modeling and analysis of surface waves at the boundary of two metamaterials are presented. The nature of the phenomenon of the surface-plasmon-polaritons and the influence of various parameters on it are investigated. We have analyzed the properties of structures incorporating nanostructured metamaterials. Surface-plasmon-polaritons at the interface of such metamaterials are studied. We demonstrate the ways to control the properties of the surface waves. Each metamaterial comprises alternating metal and dielectric layers. We analyze the dependence of the dispersion characteristics on the materials employed in metal-dielectric compound. The consistency of the dispersion diagrams and effective permittivity is studied. The Drude model is introduced in the metal dispersion in order to take into account the effects of the structure on dielectric properties.

Clifford's Geometric Algebra provides an elegant formulation of Maxwell's equations in the spacetime setting. Its clear geometric interpretation is used to derive a goal function, whose minimization results in Hodge-optimized material matrices being diagonal or diagonal-dominant. Effectively it is an optimization of the primal/dual mesh pair of a finite difference based discretization scheme taking into account the material properties. As a research example a standing wave in 2D cavity filled with an anisotropic material is investigated. Convergence of the scheme for various choices of mesh pairs is discussed. The limitations of the method in the 3D case are presented.

This paper presents a very simple comb shaped single layer microstrip patch antenna with seven operating bands for wireless systems. Eight symmetrical rectangular strips are connected by a single strip to achieve multiple operating bands. The proposed antenna provides maximum number of resonating bands compared to the antennas of its class. Effects of additional strips and the connecting strip on the antenna characteristics are studied. A prototype of the antenna is fabricated for experimental validation. The measured reflection coefficient (S₁₁) and radiation patterns are in good agreement with their simulated counterpart. Measured result shows that the proposed antenna can operate at seven different frequency bands 1.56-1.64 GHz, 1.76-1.94 GHz, 3.62-3.74 GHz, 4.43-4.48 GHz, 5.02-5.13 GHz, 5.48-5.62 GHz and 5.92-6.02 GHz. These bands cover some of the most useful bands for wireless systems such as GPS (1570.42-1580.42 MHz), DCS-1800 (1710-1880 MHz), PCS-1900 (1850-1990 MHz), WiMAX and WLAN.

In this paper, a new compact coplanar waveguide (CPW) ultrawideband (UWB) antenna with an electronically tunable notched band is proposed for an overlay onto cognitive radio (CR) systems. The proposed antenna utilized a rectangular microstrip resonator in the bottom layer to create a single notched band and to realize tunability and miniaturization using varactors. The center frequency of the notched band can be electronically tuned by changing the effective electrical length of the microstrip resonator, which is achieved by employing two varactor diodes at the resonator edges. Moreover, the simple biasing of the varactor diodes has a small effect on the antenna performance. Experimental results show that the proposed antenna can selectively have a band notch over a continuous operating band about 1.44 GHz from 4.77 to 6.21 GHz to prevent the interference to the primary users that are operating in this band such as the WLAN (5.15-5.35 GHz; 5.725-5.825 GHz) and the WiMAX (5.25-5.825 GHz). Good agreement is found between the simulated and the measured data.

The degree of polarization (DoP) can be utilized as a detection statistic in the polarimetric radar to achieve target detection performance improvement. In this paper, a polarimetric radar model is established, which includes reflections from both target and clutter at first. Then, probability density functions (PDFs) of the estimated DoP are expressed in closed form, which is derived from joint eigenvalue distributions of complex noncentral Wishart matrices. The detector is developed and evaluated theoretically on the basis of the statistical properties of the DoP. Finally, a comparison between the new DoP detector and single-polarization detector is presented against real data. The performance improvement is demonstrated by the comparison results.

In this paper, an ultra compact dual-band metamaterial antenna based on a new asymmetric generalized negative refractive index transmission line is introduced. The antenna is designed to support the 900 MHz GSM and 2400 RFID/WiFi bands. Moreover, the antenna size is only (15×20 mm²) which is only less than (0.08λ_g× 0.1λ_g) at the center frequency of the first resonance and (0.22λ_g× 0.29λ_g) at the center frequency of the second resonance. The theoretical design steps of the antenna are explained. The dual-band antenna design has been validated using equivalent circuit modelling, electromagnetic full wave simulations and practical measurement. The results illustrate that the antenna has the first resonance centred at 0.9 GHz and the second at 2.4 GHz with 15 dB return loss in the two bands. Good agreements among the circuit modelling, electromagnetic full wave simulation and practical measurements have been achieved.

The model for penetration of a wire braid is rigorously formulated. Integral formulas are developed from energy principles for both self and transfer immittances in terms of potentials for the fields. The detailed boundary value problem for the wire braid is also set up in a very efficient manner; the braid wires act as sources for the potentials in the form of a sequence of line multipoles with unknown coefficients that are determined by means of conditions arising from the wire surface boundary conditions. Approximations are introduced to relate the local properties of the braid wires to a simplified infinite periodic planar geometry. This is used to treat nonuniform coaxial geometries including eccentric interior coaxial arrangements and an exterior ground plane.

A compact dual-polarized antenna element integrated with balun is proposed. Two pairs of dipoles are employed for the dual-polarizations of the antenna, and strong mutual coupling between them is introduced to widen the bandwidth of the antenna. Bent dipoles are used to reduce the size of the antenna. The simulated and measured results show that the proposed antenna can cover the bandwidth ranging from 790 MHz to 960 MHz with VSWR < 1.5 and isolation > 26 dB. The antenna element is also fabricated and tested. The measured results show that the antenna can be a good candidate for the design of European Digital Dividend/CDMA800/GSM900 mobile communication base station antenna.

It has been widely verified that the hybrid finite element - boundary integral - multilevel fast multipole algorithm (FE-BI-MLFMA) is a general, efficient and accurate method for the analysis of unbounded electromagnetic problems. A variety of fast methods of FE-BI-MLFMA have been developed since 1998. In particular, the domain decomposition methods have been applied to FE-BI-MLFMA and significantly improve the efficiency of FE-BI-MLFMA in recent years. A series of fast domain decomposition methods (DDMs) of FE-BI-MLFMA have been developed. These fast DDMs can be roughly classified into two types: Schwarz DDMs and dual-primal finite element tearing and interconnecting (FETI-DP) DDMs. This paper will first give an overview of the DDMs development of FE-BI-MLFMA. Then a uniform, consistent, and efficient formulation is presented and discussed for these fast DDMs of FE-BI-MLFMA. Their computational complexities are analyzed and studied numerically.

Multispectral imaging is an important tool for understanding composite materials in many disciplines. Spectral unmixing enables the determination of individual fluorophore distributions. Due to the dispersive nature of biomaterials the observed spectra of fluorescent dyes is unknown. Spectral unmixing can be accomplished for unknown endmember spectra using minimum volume simplex analysis (MVSA). Compressive sampling (CS) is a method to reduce the computational cost of operating on sparse data sets and can be performed efficiently using NESTA based on Nesterov's algorithm. Here we demonstrate that NESTA and MVSA can be combined with a denoising threshold to create a compressive sampling and multispectral unmixing (CSMIU) method that enables efficient bioimaging and unmixing with high levels of accuracy (spectral angle distances (SADs) < 0.05). This CSMIU method may potentially enable broadband and in vivo bioimaging modalities.

Static charging of an aircraft surface can lead to electromagnetic disturbances on aircraft radio and avionic systems. This phenomenon is called Precipitation Static. Arc discharges are the main causes, and they often occur when there is a bonding defect on the surface of the aircraft. In order to find these bonding defects, often the whole aircraft has to be scanned. This paper presents a method that aims at reducing the time needed for the search of outer bonding issues. The system is composed of an instrumentation to be used in-flight, that measures the electromagnetic emissions of P-Static sources using several sensors placed on the surface of the aircraft. Then, given several signals measured from sensors and using a time domain location method based on delay estimation, it is possible to compute the source position. The method is validated on a simplified fuselage mock-up with satisfying location performance.

It is shown in this paper that the problem of reducing the number of elements for multiple-pattern arrays can be solved by a sequence of reweighted ℓ₁ optimizations under multiple linear constraints. To do so, conjugate symmetric excitations are assumed so that the upper and lower bounds for each pattern can be formulated as linear inequality constraints. In addition, we introduce an auxiliary variable for each element to define the common upper bound of both the real and imaginary parts of multiple excitations for different patterns, so that only linear inequality constraints are required. The objective function minimizes the reweighted ℓ₁-norm of these auxiliary variables for all elements. Thus, the proposed method can be efficiently implemented by the iterative linear programming. For multiple desired patterns, the proposed method can select the common elements with multiple set of optimized amplitudes and phases, consequently reducing the number of elements. The radiation characteristics for each pattern, such as the mainlobe shape, response ripple, sidelobe level and nulling region, can be accurately controlled. Several synthesis examples for linear arrays, rectangular/triangular-grid and randomly spaced planar arrays are presented to validate the effectiveness of the proposed method in the reduction of the number of elements.

We present a description of the electromagnetic field for the propagation invariant beams using scalar potentials. Fundamental dynamical quantities are obtained: energy density, Poynting vector and Maxwell stress tensor. As an example, all these quantities are explicitly calculated for the Bessel beams, which are invariant beams with circular cylindrical symmetry.

In this paper, a microstrip-fed hexagonal shape ultra-wideband (UWB) monopole antenna with triple band-notched characteristics is presented. The antenna consists of a microstrip feed line, a regular hexagonal shape radiation patch with a complementary split ring resonator (CSRR) and a pair of inverted T-shaped conductor-backed planes embedded in the antenna backside. Notched bands can be easily controlled by geometry parameters of the CSRR and conductor-backed planes. The simulated and measured results show that this monopole UWB antenna can offer an operation frequency from 2.93 GHz to 10.04 GHz with -10 dB return loss bandwidth, except three notched bands at 3.31-3.78 GHz, 5.33-5.77 GHz and 7.24-7.72 GHz for rejecting the WiMAX and downlink of X band satellite communication system signals. A good agreement between the measured and simulated results is observed. The proposed antenna provides broadband impedance matching, appropriate gain and stable radiation patterns over its operating bandwidth and can be used in wireless UWB applications.