An effective design of a novel, compact, single feed, dual patch frequency reconfigurable Microstrip Patch Antenna (MPA) for wireless communication systems is proposed and studied in this paper. Fundamental structure of the antenna consists of a rectangular patch and a U-shaped patch. This antenna occupies a compact volume of 86.3 mm × 50 mm × 1.5875 mm (6850.6 mm³) including ground plane. Switching among four different frequencies is obtained by varying effective length of antenna. Effective length is changed by placing three PIN diodes at different positions in the slot present between two patches of the antenna. Variations in effective length perturb the surface current paths and hence change current density on the conducting patches. By changing states of PIN diodes, the proposed antenna could be switched to 1.87 GHz, 3.55 GHz, 3.67 GHz and 5.6 GHz frequencies. Antenna is simulated in High Frequency Structure Simulator (HFSS) Version 13.0, and a prototype of the simulated antenna with DC biasing circuit is fabricated on a flame retardant (FR-4) Epoxy substrate. The antenna is fed by an inset microstrip line which provides impedance matching. The prototype is tested for its performance analysis. A good agreement is obtained between measured and simulated results. Simulated and measured results show that the antenna provides return loss less than -10 dB assuring good match in absence of any matching network at all frequencies. Effect of changing the position of PIN diodes on resonance frequencies is also studied. The proposed antenna provides benefits such as multifunction operation and symmetry of radiation pattern upon switching between different frequencies.

In this study, new closed-form solutions are presented for deriving inductance and capacitance elements of the extended-composite right/left-handed transmission line (E-CRLH TL) unit cell from the cutoff frequencies of right-handed (RH) and left-handed (LH) bands. The characteristics of the E-CRLH TL are investigated. The dispersion diagram, Bloch impedance, S-parameters are analyzed by the TL, circuit theories and the Bloch-Floquet theorem. Lastly, the usefulness of our method has been shown in detail by designing the desired characteristics for various cases.

This paper investigates the cogging torque and torque ripple in high pole number interior permanent magnet generators, designed for direct-drive applications. Two interior permanent magnet rotor topologies --- flat-shaped and V-shaped were considered with distributed wound and fractional slot concentrated wound stators. A comparison of torque performances was made between distributed wound and fractional-slot concentrated wound generators. Cogging torque was minimized by finding an optimum magnet pole arc length and torque ripples were minimized by finding optimum slotopening and flux barrier shape. Design analysis was carried out in finite element models. It was found that flat-shaped rotor topology in the fractional slot concentrated wound stator can provide the best torque performance regarding low cogging torque and torque ripple. This finding was verified in constructed prototype machine.

This paper presents the modeling and simulation of a new rectangular ferrite-loaded waveguide based on left-handed metamaterial (LHM) unit cells at K_u-band. The structure has an 8×8 unit cell configuration, whose negative permittivity and negative permeability are achieved by metallic wires array and ferrite medium, respectively. The equivalent circuit model and transmission parameter matrix for the unit cell are presented based on microwave two-port network theory. The operating frequency is in the TE₁₀ single mode range at 12.97-15.90 GHz where magnetic and electric resonances are coupled simultaneously. The finite-element method (FEM) based simulation software HFSS has been used to set original model and optimized model with vacuum layers for decoupling. Analysis of 3D electromagnetic waves propagation and scattering parameters demonstrate the backward wave property of the optimized waveguide. Negative propagation constant and negative index of refraction are calculated based ona method for extracting effective parameters of LHM. The proposed structure has scalability, double negative, and broad-band operation characteristics in the electromagnetic paradigm.

In this paper, a new analytically regularizing method, based on Helmholtz decomposition and Galerkin method, for the analysis of the electromagnetic scattering by a hollow finite-length perfectly electrically conducting (PEC) circular cylinder is presented. After expanding the involved functions in cylindrical harmonics, the problem is formulated as an electric field integral equation (EFIE) in a suitable vector transform (VT) domain such that the VT of the surface curl-free and divergence-free contributions of the surface current density, adopted as new unknowns, are scalar functions. A fast convergent second-kind Fredholm infinite matrix-operator equation is obtained by means of Galerkin method with suitable expansion functions reconstructing the expected physical behaviour of the unknowns. Moreover, the elements of the scattering matrix are efficiently evaluated by means of analytical asymptotic acceleration technique.

We present a new approach based on numerical constructions of testing functions for improving the accuracy of the magnetic-field integral equation (MFIE) and the combined-field integral equation (CFIE) with low-order discretizations. Considering numerical solutions, testing functions are designed by enforcing the compatibility of the MFIE systems with the accurate coefficients obtained by solving the electric-field integral equation (EFIE). We demonstrate the accuracy improvements on scattering problems, where the testing functions are designed at a single frequency and used in frequency ranges to benefit from the design procedure. The proposed approach is easy to implement by using existing codes, while it improves the accuracy of MFIE and CFIE without deteriorating the efficiency of iterative solutions.

Metamaterials have been previously loaded with diodes and other types of passive circuit elements. Transistors offer an alternative to these established loading elements to expand the possible capabilities of metamaterials. With embedded transistors, additional degrees of freedom are achieved and lay out the architecture for more complex electromagnetic metamaterial design. A mathematical analysis of transistor loaded SRR unit cells is described in which the transistor acts as a variable resistor. From the mathematical analysis, we calculate transmission coefficients for a single unit cell. We then experimentally measure two SRRs with tunable quality factors and thus tunable bandwidth based upon modulating the effective loading circuit resistance to confirm the calculations. From the agreement between the calculated and measured transmission coefficients, we expand the analysis to show that a slab of more densely packed unit cells can achieve negative permeability with varying degrees of dispersion.

A novel low radar cross section (RCS) microstrip patch antenna array (1×4) (MSPAA) is reported in this paper. A thin and wideband radar absorber (RA) based on a single octagonal loop (SOL) resistive frequency selective surface (FSS) is designed for realizing out-of-band RCS reduction of the MSPAA from 6.2 GHz to 18 GHz. The RA is designed for -15 dB reflectivity from 6.2 GHz to 18 GHz. Embedded Passives (EP) resistors are used for implementing the resistors as integral to the substrate with no soldering at all which results in a quantum improvement in reliability. Full wave analysis of the low RCS MSPAA with the RA is carried out using HFSS. RCS measurements are performed, and an RCS reduction of 6 to 18 dB is attained compared to the reference antenna array over a wide band from 6 GHz to 18 GHz, with no degradation in VSWR and gain of the antenna array. The thin and wideband RA with its low weight and flight worthy constituent materials can be applied independently as skins of a stealthy UAV configured primarily for low RCS with external shaping, and the proposed antenna array can be used without modifications, as a low RCS conformal antenna structure.

The simulation of multi-layer rough surfaces is an indispensable step in passive radiation imaging, to which little attention has been paid so far. Based on the existing model of brightness temperature tracing described in our recent works, diffused transmission of the bottom layer is taken into account in the improved model which is presented in this paper. Then, a method called multi-layer brightness temperature tracing method (MBTT) is established to obtain the brightness temperature of a rough surface, and the applied range of the simulation in passive millimeter-wave imaging (PMMW) is extended.

In fixed-receiver bistatic synthetic aperture radar (SAR), the spaceborne SAR is used as an illuminator. The direct-path signal and bistatic SAR raw data are sampled by the fixed-receiver which is placed on the top of a building or a hill. As the direct-path signal has high signal-tonoise ratio (SNR) advantage and almost the same synchronization error terms, it is used as the reference signal for the range matched filtering. Then the range compression can be realized with a time and frequency synchronization process. However, after range match filtering by the directpath signal, the range history of point target consists of three square-root terms, for which it is hard to use the Principle of Stationary Phase (POSP). Meanwhile, the two-dimensional (2-D) spatial variation of the target's 2-D frequency spectrum is serious. By combining azimuth preprocessing, directpath signal compensation and nonlinear Chirp Scaling (NLCS) imaging algorithm, a new focusing algorithm is presented in this paper. Simulation results of point targets are presented to validate the efficiency and feasibility of the proposed imaging algorithm. Finally, this algorithm is also validated by the measured data which is obtained using the HITCHHIKER system.

A new design of non-planar magneto-electric monopole antenna is proposed and presented. This antenna consists of a novel design of electric monopole with dual Ί shaped feed line design and possesses 61.5% impedance bandwidth, from 4.5 GHz-8.5 GHz. The antenna exhibits stable omnidirectional radiation pattern with almost identical E-plane and H-plane radiation patterns and also provides a peak gain of 7.4 dBi. Due to its good electrical characteristics and radiation parameters, the antenna has great capability to operate in C band, to overcome the challenges of multi-frequency applications.

This work investigates on the performance improvements in terms of sidelobe reduction provided by arrays organized into randomly overlapped subarrays (ROSAs) in comparison to other subarray arrangements such as contiguous and uniformly-overlapped modules. This configuration can be advantageous for applications that need to scan over a limited angular sector. The performance of the ROSA design is thoroughly analyzed for different degrees of overlapping in terms of scan losses, minimization of peak side lobe level, number of components and array size.

In this paper, a CPW feed ultrawideband (UWB) slot antenna with a single reconfigurable notched band is proposed for overlay cognitive radio (CR) systems. The proposed antenna utilizes two symmetrical short circuited quarter wavelength resonators at the top layer and close to the ground to create a single notch. The switching reconfiguration is achieved by changing the length of resonators to prevent the interference to the primary users that are operating in the wireless local area network (WLAN) band at 5.725-5.825 GHz and the international telecommunication union (ITU) band at 8.05-8.4 GHz. The center frequency of the notched band can be tuned by selecting the length of the resonators, which is achieved by employing two ideal switches. Moreover, the proposed antenna has been fabricated and tested. The experimental data confirmed that the proposed design can selectively have a band notch over the two existent desired bands.

This article presents a method to characterize stochastic observables defined by induced surface currents and fields in electromagnetic interactions with uncertain configurations. As the covariance operators of the stochastic distributions and fields are not compact, a strict Karhunen-Loeve (KL) approach is not possible. Instead, we apply a point-spectrum regularization by expanding the stochastic quantities on a finite-element-like basis. The coefficients of the KL expansion are approximated analytically in a polynomial-chaos (PC) expansion. The novelty of our approach resides in its ability to handle multiple PC expansions simultaneously and determine the orders of the KL and PC expansions adaptively. Thismethod is illustrated through the example of the voltage induced at the port of a random thin-wire frame illuminated by random plane waves. The results show the accuracy and computational efficiency of the proposed method, which provides a complete characterization of the randomness of the observable.

A ground-based radio occultation (RO) technique is proposed to retrieve the atmospheric refractivity profile around a specific region at a higher sampling rate than conventional space-based RO techniques, making it more suitable for regional weather studies. A harmony search (HS) algorithm with ensemble consideration (HS-EC) based on atmospheric physics is proposed to retrieve the refractivity profile more efficiently without being trapped in suboptimal solutions. The highest altitude of profile is extended to 95 km from 40 km adopted in conventional ground-based RO techniques, leading to more accurate results.

Using the program of numerical simulation of ultrawideband pulse reflection from dielectric medium with random rough surface, a possibility to detect ideally conducting objects placed near the surface was investigated. Medium parameters corresponded to the cases of the dry and wet sandy ground. Based on the correlation analysis of the reflected objects with orthogonal polarizations, a decision about the presence or absence of an object was made. An ideally conducting rectangular object was buried into the ground with a random rough surface to different depth. A cross-shaped metal object was disposed above the surface.

A novel high-gain directional lens antenna is numerically designed and experimentally tested in terahertz atmospheric transmission I window. The lens antenna consists of two components: a diagonal horn is adopted as the primary feed antenna, and a multilayer stacked lens consisting of the concentric hatch-crosses is used to focus the electromagnetic waves. The far-field characteristics of the horn antenna and the lens antenna are both studied. Furthermore, the effects of the number of periods of the lens and the focus diameter ratio on radiation characteristics are studied by using variable-controlling approach. The experimental results show that both the diagonal horn antenna and the lens antenna have axisymmetric radiation patterns. The gain of the horn antenna ranges from 23.8 dB to 24.9 dB, and the 3 dB main lobe beamwidth varies from 10.8° to 12.4°. The gain of the lens antenna is higher than 26.4 dB, and the 3 dB main lobe beamwidth is lower than 4.8° across the operation bandwidth. The good focusing characteristics and great directionality indicate that the designed lens antenna is qualified for applications in THz wireless communication systems.

There are applications of the finite difference time domain (FDTD) method, which need to model thin wires in dispersive media. However, existing thin wire techniques in the FDTD method are developed only for the conductive and dielectric media. The article presents a modification of oblique thin wire formalism proposed by Guiffaut et al. and a minor modification for the technique proposed by Railton et al. for applications with Debye media. The modifications are based on auxiliary differential equation (ADE) method. The modifications are validated by calculations of grounding potential rise (GPR) of a horizontal electrode buried in soil with dispersive properties.

In this paper we demonstrate how so-called polynomial chaos expansions can be used to create efficient algorithms for uncertainty quantification in some classes of problems related to wave propagation in stochastic environment. We provide an example from telecommunication.

This paper presents the design of a compact printed multi-band antenna for satellite communications within vehicular applications. The designed antenna is characterized by its compact size of 24mm18mm and multiple resonances over WiMAX, WLAN, 5 GHz U-NII, C-band, X-band, Ku-band, Kband and Ka-band. The performance of the multi-band antenna is investigated, and its equivalent circuit model is presented. Good performance is achieved over all the operating bands, with a relatively high gain and efficiency. Furthermore, as the interference with coexisting wireless systems can have a severe impact on the performance of the antenna, four variants of the antenna are proposed incorporating band rejection features within the antenna design. Embedded quarter-wavelength spur-lines, slots, and parasitic elements were used.