A flexible VHF/UHF Vivaldi antenna is proposed. The antenna is realized on 600 × 600 mm² silicone substrate with a thickness of 1.5 mm. The silicone substrate is used due to its low cost, its robustness and its flexibility. The antenna has a 6-dB impedance bandwidth from 150 MHz to 10 GHz. The measurements have shown that the bending slightly affect the impedance and the radiation patterns of the antenna. This last one is used for military applications to receive and find the source of VHF/UHF micro-wave emissions.

This paper presents a new approach for the realization of RF switches based on the Conductive Bridging Random Access Memory technology (CBRAM). This promising approach allows the realization of RF switches in an extremely simple manner at low cost. For the first time, an RF switch based on a MIM structure is realized with an insulator layer obtained from a commonly used resin deposited by spin coating. The paper reports a RF switch based on CBRAM and demonstrates a device integration onto plastic circuit board (PCB). The realized switch is validated by experimental measurements for a frequency range up to 1.5 GHz with an activation voltage less than 1 V.

Based on a proposed inexact Hodge decomposition, this paper describes a viable scheme using the second order finite elements in the T-Ω method considering multiply-connected regions for the eddy current problems. Several numerical examples have been presented to demonstrate the effectiveness of this scheme.

Ring resonators are very commonly used for the design of frequency selective surfaces (FSSs). But, for some particular design, the spacing between the resonators becomes very small. So it leaves no space to shift the reflection band towards the lower side of the spectrum. It also becomes very difficult to realize large PCBs. In this paper, an improvised design of the ring resonator using stubs is reported. This provides the designer with some flexibility. Two different configurations using this concept have been fabricated. Measured results are compared with the configuration using conventional ring resonators. These results indicate good performance with tune-ability in the response without major change in the design or in the substrate.

In this article, the mixed potential integral equation is discretized using the Rao-Wilton-Glisson basis functions in order to obtain a method of moments matrix equation for a source reconstruction problem. The weighting functions used in the setup of the moments equation are Dirac delta functions. The entries of the moments matrix are computed using a semi-analytical method which is applicable to any method of moments problem with point matching. The analytical calculation is made possible by employing a differentiation property of the scalar Green function and the properties of the mesh elements of the source plane. The semi-analytical method makes it easier to increase the accuracy of the moments matrix elements. The accuracy of the method is shown by comparing the results obtained using the semi-analytical method to those obtained by a fully numerical procedure.

The discontinuous Galerkin's (DG) method is an efficient technique for packaging problems. It divides an original computational region into several subdomains, i.e., splits a large linear system into several smaller and balanced matrices. Once the spatial discretization is solved, an optimal time integration method is necessary. For explicit time stepping schemes, the smallest edge length in the entire discretized domain determines the maximal time step interval allowed by the stability criterion, thus they require a large number of time steps for packaging problems. Implicit time stepping schemes are unconditionally stable, thus domains with small structures can use a large time step interval. However, this approach requires inversion of matrices which are generally not positive definite as in explicit shemes for the first-order Maxwell's equations and thus becomes costly to solve for large problems. This work presents an algorithm that exploits the sequential way in which the subdomains are usually placed for layered structures in packaging problems. Specifically, a reordering of interface and volume unknowns combined with a block LDU (Lower-Diagonal-Upper) decomposition allows improvements in terms of memory cost and time of execution, with respect to previous DGTD implementations.

Performance of a harmonic transponder strongly depends on the properties of the antenna and diode used, which makes finding a good combination of them very important. For a transponder with a fixed antenna geometry, the effect of different diodes is analyzed through electromagnetic simulations and theoretical calculations. The antenna used in the transponder is directly matched to the impedance properties of a particular diode. Effects of both detector and varactor diodes on the return loss characteristics of the antenna and the obtainable transponder response are observed. Criteria for selecting a suitable diode are given. Benefits and drawbacks of using different antenna matching techniques are discussed, and principal design steps are given both for transponders matched directly to the antenna and for transponders with external matching circuits.

This paper presents a wideband circular polarization antenna for Global Navigation Satellite System (GNSS). By exciting four slots etched along each edge of a square ground with equal amplitude and 90° phase difference, good circular polarization performance is achieved. A novel radiation element, composed of back-side slot and front-side monopole, is proposed to realize a wideband radiation. Meanwhile, the feed network composed of Schiffman phase shifters and Wilkinson power dividers maintains this wideband performance. A backed cavity is used to suppress the backward radiation, therefore enhances the frontward gain. Measured results of the fabricated antenna show good agreement with the simulated ones. The main advantages of this antenna include its wide bandwidth, good circular polarization, high front to back ratio, low cost, and easy fabrication, which make it very attractive for GNSS terrestrial applications.

A new approach to design a dual-band matching network using a dual-band quarter-wave line is presented. The proposed matching network is capable of simultaneously matching frequency-dependent complex loads (FDCLs) having different values at two arbitrary frequencies to a real source impedance, Z₀. A very simple step-wise design procedure is discussed for the transformer along with closed-form design equations which are very simple in nature. For experimental verification, two PCB prototypes have been fabricated using FR-4 material, operating at 1 GHz and 2.42 GHz. The measurements results matches well with that obtained from simulation, exhibiting good performance.

In this letter, a novel frequency-reconfigurable monopole antenna with several switchable states including an ultra wideband (UWB) state, filtering narrowband states, and a tunable filtering band state is presented. The antenna, which supports most applicable overlook narrowband frequencies between the 2-6 GHz, can be used in multiradio wireless systems. Moreover, the proposed antenna, which can avoid UWB interference and has narrowband functionality, has good potential for use in cognitive radio.

Microwave oven generates a harmful electromagnetic wave at 2.45 GHz of 1000 Watts. The generated microwave is confined within the cavity of the oven for efficient heating and secured operation. To prevent microwave leakage through the front glass door, a special construction of Faraday Cage is involved. In this paper, Faraday Cage is replaced with Transparent Frequency Selective Surface Front Door, which provides better visibility and avoids microwave energy to escape from the oven. Two works are proposed in this paper. The first one is band pass response which has been achieved for 10 GHz by printing array of Greek cross aperture (FSS) on the front glass door, and the second work is band stop response which has been achieved for 2.4 GHz frequency by printing the array of circular ring patch (FSS) on the front glass door. Design of two different FSS arrays and the simulation results were discussed.

In this paper, a multiband flexible antenna is presented. This antenna was realized on a flexible substrate in order to realize a deployable system for a distress beacon. We used the concept of open-sleeve antenna to change a quadrupole mode into a dipole mode. The main radiating element of the antenna is a dual-band folded U-shaped antenna. The operating frequencies of this antenna are studied depending on the length of the parasitic elements. In order to understand the matching and the radiation patterns in far field of both antennas (U-shaped and open-sleeve), their magnetic behaviors in near field are studied in simulation and in measurement. The simulated and measured radiation patterns are also presented to check the study in near field.

This paper presents a tri-band bandpass filter (BPF) consisting of a wide BPF and two narrow bandstop filters (BSFs). BPF is a ninth-order interdigital structure, and BSFs are designed fifth-order series resonators with quarter wavelength transmission line connected. The selectivity of BPF and the bandwidth of BSF are analyzed using simulation software. A tri-band BPF, made of metal cavities, is designed and measured. Three passbands are located in 1.332~1.401 GHz, 1.443~1.458 GHz, 1.506~1.660 GHz, and insertion losses in passbands are less than 2.1 dB. Ratios of Δf_{40 dB} /Δf_{3 dB} are 1.9, 2.67 and 1.33, respectively, and isolation between passbands is more than 75 dB. The good agreement between the simulated and measured results validated the proposed structure.

A circular patch antenna based on open elliptical-ring slots and shorting vias with conical radiation patterns is proposed. Fed by the coaxial probe at the center of the circular patch, the proposed antenna is excited at three resonant modes simultaneously. The first resonant mode (monopolar patch mode) is achieved by six shorting vias, each of which is placed at the center of the open elliptical-ring slot. By embedding six open elliptical-ring slots on the patch, the other two resonant modes of the open elliptical-ring slot resonator, TE₁₁₀ and TE₂₁₀, can also be excited. Due to symmetrical slots on the patch, these two modes can produce conical patterns, and their frequency ratio can also be tuned by adjusting the size of the slots. The proposed antenna is fabricated and measured. The measured results show that the proposed antenna can provide three operating bands which meet the required bandwidth specifications of 2.4/5.8 GHz WLAN and 3.5/5.5 GHz WiMAX standards. Detailed design considerations of the proposed antenna are described, and both the simulated and measured results are given. Moreover, the effects of the vital parameters on the performance of the proposed antenna are analyzed in this paper.

In this article we present νFDTD (New FDTD), an efficient and accurate method for solving low frequency problems and with those non-conformal geometries by using the Finite Difference Time Domain (FDTD) method. The conventional time domain technique FDTD demands extensive computational resources when solving low frequency problems, or when dealing with dispersive media. The νFDTD technique is a new general-purpose field solver, which is designed to tackle the above mentioned issues using some novel approaches, which deviate significantly from the legacy methods that only rely on minor modifications of the FDTD update algorithm. The νFDTD solver is a hybridized version of the conformal FDTD (CFDTD), and a novel frequency domain technique called the Dipole Moment (DM) approach. This blend of time domain and frequency domain techniques empowers the solver with potential to solve problems that involve: (i) calculating low frequency response accurately and numerically efficiently; (ii) handling non-Cartesian geometries such as curved surfaces accurately without staircasing; (iii) handling thin structures, with or without finite losses; and (iv) dealing with multi-scale geometries.

The asymptotic approach to the problem of high-frequency diffraction by elongated bodies is discussed in this work. The classical expansion is shown to require the frequencies to be too high for it to be applicable. Attempts to improve the approximating properties of the asymptotic methods are discussed. It is shown that effective approximations appear under the supposition that the squared transverse dimension of the body is proportional to its longitudinal size measured in wavelengths. This is referred to herein as the case of strongly elongated body and is examined in detail. It is assumed that the body has a rotational symmetry and can be well approximated by a spheroid. The cases of axial incidence and that of incidence at a grazing angle to the axis are considered. Both the asymptotics of the induced currents on the surface and of the far field amplitude are developed. Comparison with numerical results for a set of test problems shows that the leading terms of the new asymptotics provide good approximation in a uniform manner with respect to the rate of elongation. Some effects typical for scattering by elongated bodies are discussed.

This paper presents for the first time a systematic algorithm to optimise the bandwidth for a semiconductor junction circulator with minimum magnetic bias requirements. The behaviour of the gyroelectric parameters was studied to describe the optimum biasing magnetic field for millimetre wave operation with maximum bandwidth. Perfect circulation conditions derived using a Green's function approach were analysed to determine the optimum radius and coupling half-angle for the semiconductor disk forming the circulator. Previously measured data for InSb at 77 K were used to find design parameters for optimum bandwidth of circulation at millimetre wave frequencies. The performance of the design was verified using a full-wave electromagnetic simulation package, where up to 90% 10 dB bandwidth centred at 200 GHz was achieved with magnetic biasing as low as 0.214 T.

Due to the inaccuracies in radar's measurement, autofocus including range alignment and phase compensation is always essential in inverse synthetic aperture radar (ISAR) imagery. Compressed sensing (CS) based ISAR imagery suggests that the image of target can be reconstructed from much fewer random pulses. Because the number of pulses is inadequate and the pulse intervals are nonuniform, conventional phase compensating algorithms can't work in CS imaging. In this paper, an iterative algorithm is proposed to compensate the phase errors and reconstruct high-resolution focused image from limited pulses. In each iteration, the image of target is reconstructed by CS method, and then the estimation of phase errors is updated based on the reconstructed image. By cycling these steps, well-focused image can be obtained. The smoothed ℓ₀ algorithm is used to reconstruct the image, and the idea of minimum entropy optimization is used to estimate the phase errors. Besides, a method of extracting range bins in range profile based on amplitude information is proposed, which can reduce the computational complexity and improve the speed of convergence considerably. Both simulation and experiment results from real radar data demonstrate the effectiveness and feasibility of our method.

Two-dimensional (2D) electromagnetic scattering from a target above the sea with breaking water wave is studied by a multiregional iterative analytical-numerical method that combines the boundary integral method (BIM) and the Kirchhoff approximation (KA). Based on the ``Pierson-Moskowitz'' (PM) sea surface and the LONGTANK breaking wave, a theoretical model of a target above the rough sea surface with breaking wave is built firstly in this paper. Unlike traditional sea surface, the multipath scattering between the crest of the breaking wave and the target cannot be accurately predicted based on KA alone. To improve the algorithm precision, a multiregional hybrid analytical-numerical method is proposed. In our multiregional model, the whole sea is divided into two subregions: the breaking wave and the PM sea surface. The scattering from the breaking wave and the object is well approximated by BIM, while the PM sea surfaces can be estimated very well by KA based on Fresnel theories. Taking the interaction between KA region and BIM region into account, an iterative system is developed which gives a quick convergence. The hybrid technique presented here is highly efficient in terms of computing memory, time consumed, and versatility.

Noncontact temperature measurements in industrial scenarios present great variety of difficulties (dust, vapor...). In this work, the authors study the use of a low-cost microwave power radiometers to measure the temperature of hot metal plate during its cooling with water. Two different radiometer, centred at different frequency bands, have been experimentally considered. The radiometers have been surrounded with a metal box to reduce undesirable radiation. Several experiments have been carried out, showing the ability of these radiometers to detect the cooling of the plates. A recalibration of the radiometers gain can be done to compensate the gain variation of the circuitry of the radiometers.