Search

A broadband absorber that utilizes a dispersive metamaterial and covers the entire microwave X-band (8–12 GHz) is proposed in the present study. An ideal absorber attached to the surface of a perfect electric conductor requires the permittivity of the absorbing layer to be anomalously dispersive in the targeted broad frequency band. We show that anomalous dispersion of the permittivity for the X-band can be fitted to a two-pole Lorentz oscillator model and realized with the use of a double-layered, square-loop metamaterial. We explain the connection between the two-pole oscillator model and the double-layered, square-loop metamaterial using an equivalent circuit model and present explicit design rules for the metamaterial. We fabricate a 4-mm-thick metamaterial absorber with flexible silicon rubber, a resistor element, and conductive wire using carbon and silver conductive ink. Our metamaterial absorber achieves a reflectance of less than −20 dB over the entire X-band region. [ABSTRACT FROM AUTHOR]

Large truncated spherical near-field systems with conductive or absorbing floors are typically used in the measurement of the performances of vehicle-installed antennas. The main advantage of conductive floor systems is the ease of accommodation of the vehicle under test, but their performances are affected by the interaction with the reflecting ground floor. Instead, absorbing-based systems emulating free-space conditions minimize the effect of the interaction with the floor, but generally require longer setup times, especially at lower frequencies (70–400 MHz), where bulky absorbers are typically used to improve reflectivity levels. Considering scaled measurements of a vehicle model, the performances of these two typical implementations are analyzed in the 84–1500 MHz range and compared to free-space measurements. Absorbers with different dimensions and reflectivity have been installed in the scaled measurement setup, and measured data have been investigated with proper post-processing to verify the applicability to realistic systems. Figures of merit of interest for automotive applications, like gain and partial radiated powers, have been compared to free-space to evaluate the impact of different scenarios. [ABSTRACT FROM AUTHOR]

In nowadays, two dimensional integral equations are frequently used in various different engineering and scientific studies. In solving these equations using numerical and analytical methods along wide frequency spectrums; the electrical dimensions of the objects and the complexity of their geometric structures are considered as critical computational aspects. This article offers an effective solution to solve some integral equations. Various problems of the theory of diffraction realized by perfectly conductive metal plates are reduced to these integral equations. Thus, a method for solving integral equations is proposed to understand arbitrary values of frequency parameters and strip sizes. Diffraction theory, defines the diffraction processes that occur when waves such as in the form of light, encounter different obstacles in multiples of their wavelengths with dimensions. A certain bending and deflection of waves around these barriers is characterized by diffraction theory. In dealing with diffraction theory, advanced numerical and matrix-based solutions such as the moment method and the T-matrix method are used. On the other hand, the integralbased solutions proposed in this study are used effectively. The integral-based solution obtained from this study is simulated according to the different medium permeability which is calculated with the electrical dimension varying depending on the frequency of the wave, and a graphical representation is provided. It is seen that the normalized current value at the ends of the strip is maximum for two different cases where the medium permeability is 20 and 30. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of a dipole antenna near the perfect electric conductor, perfect magnetic conductor, and artificial magnetic conductor (AMC). The phase variations due to reflector reflection coefficient and the distance between antenna and reflector are analyzed, and their effect on the antenna radiation patterns are studied for different frequencies. The cause of a null occurrence in the broadside direction of radiation pattern when using the AMC (or HIS) as a reflector is explored. It is shown that this degradation is due to the phase of the reflected waves at different angles from the reflector surface and this phenomenon may occur for any type of reflector. In the next step, a new broadband unit cell is presented. By changing the AMC reflection feature and the distance between the antenna and the ground plane for three different states, the performance of the printed dipole antenna is improved. The maximum gain of the antenna is enhanced by approximately 7 dB, 9 dB, and 9 dB for three different cases of AMC reflectors. Moreover, the 3 dB max‐gain bandwidth of the structures are 33.81%, 29.17% and 20.84%, with profile size of 0.16λ, 0.4λ, and 0.4λ, respectively. All cases of the antenna with AMC structures have been fabricated and the measurement results are presented. [ABSTRACT FROM AUTHOR]

In this paper, a coplanar waveguide (CPW) fed pot‐shaped electronic textile (E‐textile) antenna aided by rectangular ring ground plane has been proposed. The textile patch in pot form is designed by cutting triangular slots on the non‐radiating edges of the rectangular patch, which yields a broadband of 6.45 GHz. The measured antenna impedance bandwidth is from 2.15 to 8.6 GHz with a peak gain of 10.7 dB on fabricated human tissue muscle equivalent phantom model. The proposed antenna exhibits a broadside radiation pattern from 2.15 GHz to less than 6 GHz and conical radiation pattern from 6 GHz to 8.6 GHz covering wide impedance matching bandwidth (S11 ≤ −10 dB) of 120% for dual‐mode off and on‐body communication. In CPW fed technique, the back radiation from the antenna to on body is reduced by using a perfect electric conductor. For wearable applications, considering human safety concern the specific absorption rate levels are maintained, that is less than 1.6 W/kg limit over the operating bandwidth according to IEEE C95.1‐1999 standard averaged over 1 g of tissue model. [ABSTRACT FROM AUTHOR]

The generalized Debye source representation of time-harmonic electromagnetic fields yields well-conditioned second-kind integral equations for a variety of boundary value problems, including the problems of scattering from perfect electric conductors and dielectric bodies. Furthermore, these representations, and resulting integral equations, are fully stable in the static limit as ω → 0 in multiply connected geometries. In this paper, we present the first high-order accurate solver based on this representation for bodies of revolution. The resulting solver uses a Nyström discretization of a one-dimensional generating curve and high-order integral equation methods for applying and inverting surface differentials. The accuracy and speed of the solvers are demonstrated in several numerical examples. • Efficient solver for wideband electromagnetic scattering from bodies of revolution. • Thorough discussion of the evaluation of modal Green's functions. • Computation of high-fidelity radar cross sections. • Numerical examples demonstrating that high-order accuracy is basically required for high-frequency calculations. [ABSTRACT FROM AUTHOR]

This paper employs the spectral domain approach for full wave analysis of metal strip grating on grounded dielectric slab and microstrips shielded with either Perfect Electric Conductor (PEC) or Perfect Magnetic Conductor (PMC) walls. The modal relations between these structures are revealed by exploring their symmetries. It is derived analytically and validated numerically that all the even and odd modes of the latter two (when they are mirror symmetric) find their correspondence in the modes of metal strip grating on grounded dielectric slab when the phase shift between adjacent two unit cells is 0 or n. Extension to non-symmetric case is also made. Several factors, including frequency, grating period, slab thickness and strip width, are further investigated for their impacts on the effective permittivity of the dominant mode of PEC/PMC shielded microstrips. It is found that the PMC shielded microstrip generally has a larger wave number than the PEC shielded microstrip. [ABSTRACT FROM AUTHOR]

The electric and magnetic field expressions of guided waves in three-layer planar waveguide containing strong chiral material have been investigated theoretically. All three layers are parallel to the walls of the waveguide. Middle layer of the waveguide is filled with the air however the other two layers are filled with strong chiral material. The behavior of field intensity in different regions of the waveguide is discussed. It is shown that the location of maximum field intensity is shifted by changing the source frequency and modes of waveguide. [ABSTRACT FROM AUTHOR]

This work extends the mathematical formulation of the iterative-field-matrix method for observed data from the near-field region of a Perfect Electric Conductor. The method is used as a diagnosis tool for reflector antennas, to determine the positions and extent of distortions from their idealized shapes. The new formulation is tested on a reflector antenna with several significant bumps, and excellent results are achieved. This work also presents an example where the Method of Moments is used to generate the synthetic data and the inversion is performed using Physical Optics. Such a configuration ensures that the forward model is unbiased with respect to the inversion model, demonstrating that the new formulation is also robust for these realistic scenarios. [ABSTRACT FROM PUBLISHER]

The article investigates the application of three different ground planes for antenna performance enhancement. They are the conventional perfect electric conductor, the perfect magnetic conductor and their combination. A half-wavelength dipole in free space is considered as the reference case and its performance over these ground planes is investigated and compared.