A fully printable and conformal antenna array on a flexible substrate with a new Left-Handed Transmission Line (LHTL) phase shifter based on a tunable Barium Strontium Titanate (BST)/polymer composite is proposed and computationally studied for radiation pattern correction and beam steering applications. First, the subject 1×4 rectangular patch antenna array is configured as a curved conformal antenna, with both convex and concave bending profiles, and the effects of bending on the performance are analyzed. The maximum gain of the simulated array is reduced from the flat case level by 34.4% and 34.5% for convex and concave bending, respectively. A phase compensation technique utilizing the LHTL phase shifters with a coplanar design is used to improve the degraded radiation patterns of the conformal antennas. Simulations indicate that the gain of the bent antenna array can be improved by 63.8% and 68% for convex and concave bending, respectively. For the beam steering application, the proposed phase shifters with a microstrip design are used to steer the radiation beam of the antenna array, in planar configuration, to both negative and positive scan angles, thus realizing a phased array antenna.

The resonant characteristics of superconducting rectangular microstrip patch antenna with a superstrate layer are investigated using a full-wave spectral analysis in conjunction with the complex resistive boundary condition. The complex surface impedance of superconducting patch is determined using London's equation and the two-fluid model of Gorter and Casimir. Numerical results using the full-wave analysis presented here are in excellent agreement with theoretical and experimental results available in the open literature. Numerical results show that the effect of the superstrate layer on the resonant frequency and half-power bandwidth of the superconducting rectangular patch is stronger than that of the structure without superstrate layer as both the thickness and permittivity of the superstrate increase. Finally, numerical results concerning the effects of the parameters of superstrate-substrate and superconducting patch on the antenna performance are also presented and discussed.

Quantitative active microwave imaging for breast cancer screening and therapy monitoring applications requires adequate reconstruction algorithms, in particular with regard to the nonlinearity and ill-posedness of the inverse problem. We employ a fully vectorial three-dimensional nonlinear inversion algorithm for reconstructing complex permittivity profiles from multi-view single-frequency scattered field data, which is based on a Gauss-Newton optimization of a regularized cost function. We tested it before with various types of regularizing functions for piecewise-constant objects from Institut Fresnel and with a quadratic smoothing function for a realistic numerical breast phantom. In the present paper we adopt a cost function that includes a Huber function in its regularization term, relying on a Markov Random Field approach. The Huber function favors spatial smoothing within homogeneous regions while preserving discontinuities between contrasted tissues. We illustrate the technique with 3D reconstructions from synthetic data at 2 GHz for realistic numerical breast phantoms from the University of Wisconsin-Madison UWCEM online repository: we compare Huber regularization with a multiplicative smoothing regularization and show reconstructions for various positions of a tumor, for multiple tumors and for different tumor sizes, from a sparse and from a denser data configuration.

A new circuit reduction algorithm for generating physically meaningful equivalent circuits for electrically small structures is proposed in this work. It makes use of the generalized Y-to-Δ transformation as well as features unique to partial element equivalent circuits (PEECs) to perform the reduction process. For a given partial element equivalent circuit, insignificant nodes are removed one by one in a prioritized order according to both user-specified cut-off frequency and threshold value. By having the freedom of choosing these parameters, this algorithm provides users an option to make a tradeoff between accuracy and simplicity of the final reduced circuit. Since the generalized Y-to-Δ transformation can keep all mutual couplings intact, the order-reduced circuit should correctly capture all physical essences of the structure being modeled. Two examples are presented in this paper to validate the proposed algorithm. The equivalent circuits obtained can indeed reflect all essential physical features, demonstrating that the algorithm is a useful tool for designing and analyzing electrically small multi-conductor structures.

A wideband antenna is designed based on the concept of equivalent magnetic dipole and electric dipole combinations with excellent radiation characteristics. Single linear polarization design with two different excitations achieves good radiation symmetry and low cross-polarization. The dual-polarization case has a 67% bandwidth and isolation better than 30 dB. The present design and construction of the antenna provides simple solutions compared with similar antennas in the literature. This design avoids loading the antenna with dielectric in the active region. The agreement between measured and simulated results is excellent. The suggested antenna construction is very simple and solves many of the problems related to the practical excitation of this antenna.

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.