This paper presents a novel low-profile antenna with a broadside radiation. The proposed design strategy consists in modifying the layout of a classical Vivaldi antenna, thus resulting in compact dimensions and a broadside radiation pattern. Two different ways of implementing the proposed design approach are presented and discussed. More specifically, experimental data referring to two prototypes on a FR4 substrate with an operating frequency of 2.45 GHz are reported. The first layout has approximately the same dimensions of a Vivaldi antenna and a directivity of about 7 dBi, the second one has more compact dimensions (the dimensions are smaller than the ones of a standard patch antenna) and a directivity of about 5 dBi.

A metamaterial based electronically controlled microstrip structure, performing as leaky wave (LW) antenna with beam steering capability was synthesized. The structure has the configuration of metamaterial transmission line(TL) composed of cascade composite right- /left-handed(CRLH) unit cells. The direction of maximum radiation is tuned via the variation of varactros' capacities incorporated to the structure. Theoretical analysis and synthesis, based on the metamaterial TL theory, was made and novel methods to realize some of the elements of the units cells are proposed. Results, received via simulation, demonstrate that the LW antenna has steering capability of the direction of maximum radiation in a range of 40°, gain changing a little, 6 dB to 7 dB, during the scanning, whereas small number of cells is enough to obtain this performance.

A printed Log-periodic dipole array (LPDA) is presented, operating over the C, X and Ku bands. The antenna feeding structure consists of two coaxial cables, in order to realize an infinite balun which provides the required broadband input matching. The second coaxial cable mirrors the first one, connected to the antenna input, and is capable of both stabilizing the antenna phase center and improving the radiation pattern. The antenna has been designed using CST Microwave Studio, with an useful frequency range of 4-18 GHz. Moreover, both simulated and measured results show that the proposed LPDA can be successfully used as an Ultra Wideband Antenna in the range 4.25-13.25 GHz, in which its phase center remains stable.

A Ka-band two-dimensional synthetic aperture interferometric radiometer called BHU-2D has been developed by Electromagnetic Engineering Laboratory of Beihang University. The radiometer obtains images in real-time benefiting from the adoption of a 1bit/2level FPGA-based correlator unit. The design and implementation of the correlator unit in BHU-2D are presented in this paper. The calibration procedures of the correlation coefficients are also presented. For the purpose of simplifying the calibration procedure, a closed form approximation is introduced and applied to BHU-2D, which is used to correct the errors caused by threshold offset of the quantizer. Error analysis of this approximation shows that the method is applicable in SAIRs. In order to verify the design and calibration method, a series of validation experiments have been conducted. Measurement results have proved that the performance of the correlation unit could meet the requirements of BHU-2D.

This paper presents a novel design approach to design in-line microstrip bandstop filter with accurate design theory and sharp skirt selectivity. This kind of bandstop filter is based on a simple coupled-line structure, indicating compact and flexible circuit layout for microstrip implementation. For a single-section bandstop filter, the scattering parameters and their constrain conditions are achieved, which provides an effective design guide for multi-section bandstop filters. Theoretical analysis indicates that the even-mode and odd-mode characteristic impedances can be easily used to determine the desired bandstop performance while the total circuit layout keeps very compact. For demonstration, seven numerical examples are designed, calculated, and compared. Finally, both experimental and simulation results of a two-section two-cell microstrip bandstop filter operating at 1 GHz are presented to verify the theoretical predications.

Label-free optical biosensors are important tools to study the kinetics, interaction and presence of (bio)chemical compounds in various fields such as biotechnology, pharma, diagnostics as well as environmental and food quality monitoring. Systems based on planar optical waveguides with input/output grating couplers are of interest as they offer multiple tuning parameters for the chip design and their high sensitivity. In the present paper, an algorithm based on the Finite-Elements Method (FEM) is proposed for finding the chip response and optimizing the sensitivity of the sensor system. Total field and scattered field coupled with the Transmission Line Transfer Matrix Method (TLTMM) are compared for the FEM. Unlike some widely used approximations, the impact of the grating depth, shape, duty cycle as well as losses and surface roughness are taken into account. Another advantage of the presented method is the possibility to implement a large part of the algorithm with commercially available FEM solver. Several practical situations are treated proving the validity of the approach against the Local Interference Method (LIME). The waveguide losses appear to be a decisive parameter for the chip design.

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.