Square slot antennas with modified edges for broadband circular polarization are presented. Slots with only stubs or notches are studied and it is found that the axial ratio (AR) bandwidth is quite sensitive to the perturbations of the stubs and notches. To further enhance the AR bandwidth, slot antennas with combination of stubs and notches are proposed and wide 3-dB AR bandwidth of 15.5% (2.45-2.86 GHz) is obtained. By placing a conducting reflector at the rear of the slot, another modified square slot antenna is designed for practical applications, which achieves a 3-dB AR bandwidth of 6.5% (2.38-2.54 GHz) and peak gain of 8.7 dBic. Agreement between simulated and measured results is satisfactory.

In this paper, a novel miniaturized branch-line coupler (BLC) operating at 1.675 GHz is proposed. Partially meandered lines and dual transmission lines equivalent technology are used as the coupler's shunt arms, producing significant reduction by more than 68% compared with the conventional coupler. Moreover, the coupler can equally divide the input signal with 90° phase of difference while maintaining the initial power from the source with a simple structure. The simulated and measured results are in good agreement. Thereby verifying the design concept.

Time domain reflectometry (TDR) offers the advantage of distributed sensing using a single transmission line sensor. In the present study, a parallel plate type non-invasive TDR sensor for structural health monitoring (SHM) of composite has been designed, modeled and experimentally tested. Five layer unidirectional glass fiber/epoxy composite specimens are fabricated. Specimens included a damage initiator in form of a cut in the central ply. The TDR sensor detects sub-surface damage in the composite non-invasively as the effective dielectric constant of the composite decreases due to the presence of delamination cracks. Previous work done on dielectrostriction is used to model the TDR response to strain changes. Qualitative agreement between theory and experimental results for strain sensing are found.

In this paper, a novel planar inverted-F antenna (PIFA) with slotted ground structure is proposed for multiband mobile communication application. The multimode performance is applied for multiband operation in our design. The proposed antenna has good impedance matching characteristics for GSM850/900, DCS1800/1900, LTE2300/2500, IEEE 802.11a/b. The measured radiation efficiency of proposed antenna is all higher than 69% in GSM (824-960 MHz)/DCS (1710-1880 MHz)/PCS (1850-1990 MHz)/LTE (2300-2400 MHz, 2500-2690 MHz)/802.11b (2.4-2.48 GHz), and is up to 50% in IEEE 802.11a (5.15-5.825 GHz).

We investigate the wave propagation properties in lossy structures with graded permittivity and permeability involving left-handed metamaterials. An exact analytic solution to Helmholtz' equation for a lossy case with both real and imaginary parts of permittivity and permeability profile, changing according to a hyperbolic tangent function along the direction of propagation, is obtained. It allows for different loss factors in RHM and LHM media. Thereafter, the corresponding numerical solution for the field intensity along the composite structure is obtained by means of a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms. We present the expressions and graphical results for the field intensity along the composite structure and compare the analytic and numerical solutions, showing that there is an excellent agreement between them.

The ability to control the scattering property of an object is important in many applications. In this paper, we propose and study the scattering characteristics of a circular array of split-ring resonators (SRRs). By calculating the scattered energy spectrum, we show that the proposed structure has a localized surface plasmon resonance like behavior, which makes it useful as a super scatterer. Furthermore, in a special case, the proposed structure exhibits transparency to the illuminated waves, i.e. it does not scatter any energy at all and thus acts as a zero electromagnetic scattering object.

Time domain analysis of electromagnetic wave propagation is required for design and characterization of many optical and microwave devices. The FDTD method is one of the most widely used time domain methods for analysing electromagnetic scattering and radiation problems. However, due to the use of the Finite Difference grid, this method suffers from higher numerical dispersion and inaccurate discretisation due to staircasing at slanted and curve edges. The Finite Element (FE)-based meshing technique can discretize the computational domain offering a better approximation even when using a small number of elements. Some of the FE-based approaches have considered either an implicit solution, higher order elements, the solution of a large matrix or matrix lumping, all of which require more time and memory to solve the same problem or reduce the accuracy. This paper presents a new FE-based method which uses a perforated mesh system to solve Maxwell's equations with linear elements. The perforated mesh reduces the requirement on memory and computational time to less than half of that compared to other FE-based methods. This paper also shows a very large improvement in the numerical dispersion over the FDTD method when the proposed method is used with an equilateral triangular mesh.

The capability of Ground Penetrating Radar (GPR) systems of accurately reconstructing the geometrical features of buried objects, when working in critical conditions, is investigated. A customized microwave tomographic approach is used to tackle the imaging through the processing of comparative experimental and synthetic GPR data. The first ones have been gathered in laboratory controlled conditions, while the second ones have been obtained by exploiting an ad-hoc implementation of a CAD tool. Attention is paid to the significant case of `strong' scatterers having size comparable to the wavelengths of the probing signal, and possibly located close to the interface where the GPR antennas move. The results from imaging point out the potential of the proposed approach, showing in particular to which extent, in challenging operational settings, it is possible to recover also the information about the shape of metallic targets in addition to their correct location and size.

In this paper, calibration of a microwave power sensor with an adaptor is investigated with direct comparison transfer technique, and mathematically modeled using signal flow-graphs together with non-touching loop rules. The developed calibration model is then implemented practically with a 30 dB attenuator as the adaptor. Its performance is evaluated following the Guide to the Expression of Uncertainty in Measurement and also verified with the Monte Carlo method. Good agreements are observed with all the error |E_n| ≤ 0.25 over the whole frequency range (up to 18 GHz).

This paper presents a cost effective and simple anti-jamming method for global positioning system (GPS) antennas in the GPS L1 (1.563-1.587 GHz) band. The proposed structure is composed of a metallic conical structure with a microstrip patch antenna, which is selected as the basic element. To overcome intentional jamming signals coming from low elevation angles, the structure is applied around the low profile patch antenna. It is found that the maximum anti-jamming performance is achieved when the lower diameter (l), height (h), and upper diameter (d) of the structure are 90, 190, and 380 mm, respectively. The experimental results show that the peak gain in the horizontal plane for the jamming signal decreases by about 6.2 dB from -6.16 to -12.36 dBic, while the peak gain in the vertical plane for the GPS signal increases by about 5.58 dB from 1.32 to 6.9 dBic. Moreover, it is shown that an improvement in the circular polarization (CP) characteristics is also obtained with the proposed structure. The measured fractional bandwidth is about 3.7% (1.561-1.62 GHz).

Magnetic response based on a two-level magnetic dipole transition in rare earth ions doped crystals was studied. Semi-classic theory and Wigner-Eckart theorem were used to calculate the magnetic permeability. It is found that negative permeability can be attained near the transition frequencies. In order to realize simultaneously negative permittivity and negative permeability, an electric dipole transition at the same frequency was also adopted, and a negative refraction region with a bandwidth of 0.57 MHz is demonstrated in (Yb_0.02 Sm_0.02Y_0.96)₃Al₅O₁₂ crystal. This explores a new route to obtain magnetic response and negative refraction at optical frequencies with nature-existed materials instead of metamaterials.

The relationship between specific absorption rate (SAR) and antenna gain inside the head due to the metal-frame spectacles was investigated. The radio frequency (RF) energy source considered is the smartphone used in the frontal face. A computer simulation using CST Microwave Studio 2012 was used for the investigation. Two sets of dipole antennas, operated at 900 MHz and 1800 MHz for GSM applications, were used as representative radiation sources from a mobile phone. Parametric studies were conducted to determine the optimum length of the metal rod, and the length was used to study the possibility of RF irradiation of the metal spectacles model. Then, the spectacles model was used as an analysis tool to study the interaction between gain and SAR in the head. The radiation pattern was plotted to identify the causes of the interactions. The gain decreased when the energy source was very close to the spectacles, and SAR increased enormously.

Application of electric field in normal to aligned carbon nanotubes creates Coulomb forces at intertube junctions and tubes become closely packed. Packed structure facilitates intertube transfer of carriers and reduced resistance is found to scale with field strength. Aggregated nanotubes are therefore used as field sensors and sensitivity is evident by drastic fluctuations of resistance. Sensing mechanism is discussed and verified.

Few works on symmetric and asymmetric dielectrics have been published, specifically the case of chiral and bi-isotropic media. For this reason, and taking into account the complexity of the studied environment, this paper treats the asymmetrical effects on the resonant frequency and the bandwidth of a rectangular microstrip patch antenna in a complex bi-anisotropic substrate-superstrate configuration. This structure is studied theoretically, and the obtained results are discussed and commented. The numerical analysis used in this paper is mainly employed in order to obtain original results. The originality of this work is presented by the bianisotropic chiral asymmetry and the combined effect of the substrate and the superstrate.

It is well known that using proper signal compression techniques, the range resolution of the radar systems can be enhanced without having to increase the peak transmits power. Whereby the range resolution is inverse proportional with the frequency band of the scanning signals, in the last period of time, in radar systems literature a lot of suitable wideband signals were designed and analyzed as performance level. However, for the large majority of these signals, the compression filter response contains significant sidelobes which may cause difficulties in the target detection and range estimation process. Consequently, in the radar signal processing theory, the sidelobes reduction techniques using synthesis of some proper nonlinear FM (NLFM) laws represents a major scientific research direction. In order to assure the sidelobes suppression, the main objective of this paper is to present an adequate synthesis algorithm of some NLFM laws based on stationary phase principle. The achieved experimental results confirm a significant sidelobes reduction (i.e., more than -40 dB) without necessity to apply some weighting techniques. Finally, the analysis of the synthesized NLFM laws by ambiguity function tool was also discussed.

A compact square dc-block bandpass filter with slots is presented. The proposed dc-block bandpass filter using square shapes produces compact size and improved performance as compared to the conventional dc-block bandpass filter using cymbal shapes. Two filters with the same dimensions provide different center frequencies respectively. In other words, the center frequency of the square bandpass filter is lower than that of the cymbal bandpass filter. The center frequency and transmission zeros can also be controlled by the slots of the square shape in the proposed square bandpass filter. The proposed square bandpass filter has an insertion loss of better than 2 dB and a return loss better than 10 dB at center frequency of 7.2 GHz. The proposed square dc-block bandpass filter is optimized by electromagnetic simulator IE3D.

In this paper, an open cavity is proposed to measure the permittivity of dielectrics. The cavity consists of an ellipsoidal mirror and two planar mirrors. The relationship between the parameters of the beam in the open cavity and the cavity geometrical parameters is presented. The transcendental equation of dielectric loaded cavity is presented, from which the permittivity of the dielectric can be solved. The resonance frequencies of the vacuum cavity and loaded cavity are computed by the resonance frequency formula and the transcendental equation. they are compared to the results from FDTD simulation. The results from two methods are almost same with each other. The advantage of the proposed open cavity over the conventional open cavity composed of spherical mirror and planar mirror is demonstrated.

The periodic structure like electromagnetic band gap (EBG) is a hot research topic in the academia and RF-microwave industry due to their extraordinary surface wave suppression property. This study involved in designing a compact uni-planar type EBG structure for a 2.4 GHz resonant frequency band. Double folded bend metallic connecting lines are successfully utilized to realize a low frequency structure while a size reduction of 61% is achieved compared to the theoretically calculated size. From the transmission response, the surface wave band gap (SWBG) is found to be 1.2 GHz (1.91-3.11 GHz) whereas the artificial magnetic conductor (AMC) characteristic is observed at 3.3 GHz. The FEM based EM simulator HFSS is used to characterize the EBG structure. The SWBG property is utilized for alleviation of mutual coupling between elements of a microstrip antenna array. A 2 x 5 EBG lattice is inserted between the E-plane coupled array which reduced the coupling level by 17 dB without any adverse effect on the radiation performances.

In this paper, an algorithm based on penalty cost function for synthesizing at-top patterns is proposed. A descent algorithm (DA) as its optimizing approach is proposed in this paper as well. Apparently, whole algorithm efficiency totally depends on the DA. Unlike traditional descent method, the DA defines step length by solving a inequality, instead of Wolf or Armijo-type search rule, stimulation results indicate that it can improve the computational efficiency. Under mild conditions, we prove that the DA has strong convergence properties. Several numerical examples are presented to illustrate the effectiveness of the proposed algorithm. The results indicate that the approach is effective in the pattern shape precisely in both mainlobe and sidelobe region for arbitrary linear arrays.

The performance comparison of two configurations of broadband Mach-Zehnder Switches exploiting, respectively, two and three waveguides, assembled into 4x4 matrices is reported in this paper. The simulations are performed by the Finite Element Method and the Finite Difference Beam Propagation Method. In particular, we have found that, to parity of maximum insertion loss, about equal to 1 dB for the single switch and 3 dB for the 4x4 matrix, the proposed three-waveguide configuration exhibits an almost doubled bandwidth Δλ=115 nm, making it suitable for efficient routing of the Wavelength Division Multiplexing signals over photonic Networks on Chip.