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.

We theoretically investigate the photonic band gaps in one-dimensional photonic crystals based on nanocomposite of silver nanoparticles. The dielectric permittivity is calculated in accordance with temperature dependence of plasma frequency of silver nanoparticle. The effect of temperature on these structures by incorporating the volume expansion coefficient of nanoparticle is analysed. The behaviors of photonic band gaps with variation of nanoparticle concentration, radii of nanoparticle, thickness of the layers and temperature are observed. The evolution of these results leads to designing the desired photonic crystals.

A problem of the spherical antenna consisting of a thin radial monopole located on a perfectly conducting sphere is solved. The antenna is excited at the base by a voltage δ-generator. An approximate analytical solution of the integral equation for the current on a thin impedance vibrator was found by the method of successive iterations. The solution is physically correct for arbitrary dimensions of the spherical antenna and for any value of surface impedance distributed along the monopole. The validity of the problem formulation is provided by using the Green's function for the Hertz vector potential in unbounded space outside the perfectly conducting sphere and by writing the initial integral equation for the current on the monopole. Influence of the monopole dimensions and surface impedance upon the radiation characteristics and the input impedance of the spherical antenna is studied by numerical evaluations using zero order approximation. The input impedance of the monopole was determined by the method of induced electromotive forces (EMF) using the current distribution function thus obtained.

PCA was effective and helpful in developing a classification system. However, it was inappropriate to perform two independent PCA models on ground truth images and query image, which was described in Figure 1 in Reference ``BRAIN MR IMAGE CLASSIFICATION USING MULTISCALE GEOMETRIC ANALYSIS OF RIPPLET, Progress in Electromagnetics Research, 137, 1-17, 2013''. In this note, we analyze the reason and revise Figure 1.

Microwave absorbers find a plethora of applications in the modern-day military and civil industries. This paper compares the performance of different variations of the Particle Swarm Optimization (PSO) algorithm to obtain optimal designs for multilayer microwave absorber over different frequency ranges, angles of incidence and polarizations. The goal of this optimization is to minimize maximum overall reflection coefficient of the absorber by choosing suitable layers of materials from a predefined database and simultaneously make the overall thickness the least practically possible. Numerical optimal results for each variation of the PSO are presented and the best results are compared with those existing in literature.

Linear array SAR (LASAR) has been attracting more and more attention for its capability of obtaining three dimensional (3D) resolutions. However, the low resolution in cross track (CT) direction limited by the length of its linear antenna array has become the bottleneck of its practical applications. To overcome this problem, we present a novel algorithm based on sparse reconstruction (SR) to improve the resolution in CT direction. First, it establishes a 1D real-valued sparse model for LASAR, which deals with the 3D image column by column along CT direction in each equi-range slice. This enables it to handle large scenes. Second, it employs the spatially variant apodization (SVA) to filter bases of the measurement matrix. As a result, the cross coherence gets suppressed as well, and it is helpful to improve the performance of sparse reconstruction algorithms (SRAs). Third, we propose the resolution enhancement ability (REA), which provides a new idea to evaluate how many times the resolution could be improved. Experimental results validate that when the signal to noise ratio (SNR) is 30 dB, LASAR could usually obtain 2 times of resolution improvement in CT direction, while the proposed method further improves the REA by a factor about 2.5. Moreover, the 3D surface terrain simulation shows a great improvement for the digital elevation map (DEM) in resolution enhancement.

This paper presents the design, simulation and measurements of wideband two-stage LNAs using commercially available discrete components and targeting Square Kilometre Array (SKA) focal-plane-array verification studies. The design optimization was implemented through simulations based on theoretical work that shows that low wide-band noise figures and power match are achievable by inner-stage component selection and device bias. In contrast to the conventional practice of having each stage of a discrete LNA matched to 50 Ω, the inner stage was designed with a mismatching capacitor between the two stages. The measured results are presented for 0.7-1.4 GHz and achieve noise figures below 0.4 dB, gain of at least 28 dB, mid-band input return loss of 7 dB, output P1dB of 18.3 dBm, input-referred IP3 of -15.47 dBm, and power consumption of 500 mW with a supply voltage of 5 V.

A novel range-instantaneous-Doppler (RID) algorithm of inverse synthetic aperture radar (ISAR) imaging based on adaptive Doppler spectrum extraction is proposed in this paper. Regarding maneuvering targets, such as military aircraft, the ISAR image is blurred on cross-range domain when the range-Doppler (RD) algorithm is applied. The RID imaging method is often used to resolve the Doppler ambiguity, but there are some scatterers that could be lost because the sliced time is fixed in traditional RID imaging. To the method proposed in this paper, the optimal Doppler spectrum of each range bin is extracted by gradient energy function (GEF) after time-frequency (TF) analysis, and then all of the optimal Doppler spectrums are combined to obtain a final 2-D RID image of the target. Compared with the traditional RID method, the novel algorithm can obtain image with better focused quality. The results obtained from simulated and field-measured data verify the superiority of the proposed algorithm.

A new class of incomplete Bessel polynomials is introduced, and its application to the solution of electromagnetic problems regarding transient wave radiation phenomena in truncated spherical structures. The definition of said special functions is introduced, and the relevant analytical properties are derived. The definition is such that the interrelationships between the incomplete polynomials parallel, as far as is feasible, those for canonical Bessel polynomials.