Search

In this letter, a miniaturized-element dual-polarized frequency selective rasorber (FSR with independently regulated dual-transmission response has been presented. The proposed FSR is made of two cascaded layers separated by an air spacer, where the top lossy layer provides wideband absorption along with in-band transmission and the bottom lossless layer exhibits a dual bandpass filter. The novelty of the proposed design lies in the use of lumped capacitors in the top layer to realize the independently controlled highly selective transmission frequencies as well as attain a miniaturized unit cell topology (having dimensions of 0.08L 0.08L, L being the lowest operating frequency . In addition, convoluted slot geometries are patterned in the bottom layer to obtain the transmission bands appearing at the same frequencies as that of the top layer. The proposed structure has an operating range of 1.87 - 7.97 GHz, whereas two distinct transmission responses are located at 3.52 GHz and 5 GHz having insertion losses of 1.2 dB and 0.82 dB, respectively. Further, the geometry exhibits an angularly stable performance upto 45o for both TE and TM polarizations. A prototype of the proposed FSR was fabricated and measured to validate the simulated responses under normal incidence

A simple optically transparent absorber based on a double complementary structured layer of indium tin oxide (ITO) deposited polyethylene terephthalate (PET) film is presented. The structure showed more than 90% absorption from 2-4.5 GHz of the frequency with a thickness of 0.0847L (wavelength corresponding to the lowest frequency of absorption band). The computed absorptivity of the proposed structure is validated using the transmission line theory and measured experimentally as well. The structure has polarization insensitive response and is highly stable for oblique wave incidence over a wide angular range. This absorber can be conformally wrapped on a curved surface and reduces the radar cross-section (RCS) by more than 10 dB of a curve cylinder. This 10 dB RCS reduction covers almost the entire S-band of microwave frequencies. Optical transparency and flexibility of the proposed absorber make it suitable for a wide range of applications.

Usually, Radar signature of an object is reduced using microwave absorber surface. Recently, another approach based on time‐modulated frequency‐selective surfaces has been developed to deceive Radar detection by selectively generating harmonics/sidebands. Here, a polarization‐insensitive time‐modulated frequency‐selective surface is proposed that works over a broad frequency range. The design employs a PIN diode‐based switchable frequency‐selective surface to switch between the two states of reflection coefficient. Monochromatic incident electromagnetic (EM) wave, upon reflection from the surface is modulated by a periodic time‐varying reflection coefficient to generate several harmonics/sidebands along with the incident frequency. In the frequency spectrum of the reflected EM wave, the power of the incident frequency component is suppressed below that of the sidebands. The time‐modulated frequency selective surface has the capability to suppress the incident frequency component for any incident EM wave in 2–4 GHz that is S band, as well as generate spurious reflection sidebands.

In this letter, three different wrapping methods i.e., circle having incisions (CI), pentagon and hexagon (P&H) and petals wrapping are proposed for covering of spherical shaped surfaces with flat microwave metamaterial absorber (MMA) without defects. To achieve the better performance, an extensive analytical study was carried for counting the number of unit cells and packing fraction in the aforementioned techniques. It was found that maximum number of unit cell can be wrapped over a spherical ball by using CI method. The maximum packing fraction was found to be in P&H method. Further, we studied variation in the number of unit cells and packing fraction for variation in the shapes (circle, square, and hexagon) and size (2–4 mm) of the unit cell. For experimental purpose, an indium tin oxide coated over polyethylene terephtalate (ITO/PET)-based conformal MMA was designed and then fabricated using excimer laser micromachining. The proposed conformal absorber gives broadband absorption from 6.21 to 15 GHz. Finally, the fabricated absorber was wrapped on a spherical ball and microwave response was measured. The measured microwave response was compared with the simulated response and found to be in good agreement with each other.

A compact five-port multi-input multi-output (MIMO) antenna for n79 (4.4–5 GHz) 5G band exhibiting pattern and polarization diversity with good isolation is proposed in this paper. This MIMO antenn...

In this paper, a compact triple-band printed monopole antenna with circular polarization (CP) has been presented for C-band wireless applications. To achieve the triple-band CP response, the top la...

Cylindrical waveguides filled with anisotropic metamaterials enable novel wave propagation phenomena. A nanoporous alumina microtube is a manifestation of such an anisotropic waveguide with an effective permittivity tensor ( $\varepsilon _{r} \neq \varepsilon _\phi = \varepsilon _{z}$ ). The metamaterial would be considered to be filled homogeneously or inhomogeneously depending on the variation of the size of the nanopores and density of the nanopores. The electromagnetic fields in such metamaterial waveguide are highly sensitive to the refractive index of the material embedded in the nanopores and the variation of the density of the inclusion in the radial direction due to the modal field distributions. We show that there is a large variation in the reflection coefficient ( $S_{11}$ ) of the inhomogeneously filled nanoporous waveguide with an embedded liquid with small variations in the material properties of the liquid. This variation in the $S_{11}$ parameter can use to determine the purity of liquid. Our results show that the permittivity variations of the inclusion material can be monitored up to the sixth decimal places theoretically. The analysis also indicates that the inhomogeneous metamaterial waveguide is more sensitive compared to both the homogeneously filled metamaterial waveguide and an isotropic waveguide covered with metamaterial clad. This waveguide has potential applications in biomedical and chemical sensing applications.

A polarization-insensitive broadband absorber with a notch band characteristic has been presented for radar cross section (RCS) reduction applications. The proposed design is a three-layered structure, consisting of metal-printed substrate layers separated by air spacers. The top layer is a resistor-loaded convoluted cross-dipole geometry that results in a wideband absorption. The band-notch response is achieved by careful design of a square loop in the middle layer, and the bottom layer is a complete metal ground. The overall structure exhibits two discrete absorption bands (having absorptivity above 90%) over the frequency ranges of 2.12 to 4.15 GHz and 6.08 to 9.58 GHz, whereas a reflective behavior is obtained from 4.3 to 5.65 GHz. The proposed geometry has several novel features, such as compact topology (with unit cell size of 0.137 λL, λL being the lowest operating wavelength), low profile, polarization-insensitivity, and wide operating bandwidth of 127.52%, unlike the existing band-notched absorbers. By deriving an equivalent circuit model and several parametric variations, the performance of the proposed absorber has been qualitatively analyzed. A sample prototype has also been fabricated and reasonable agreement among the circuit analysis, simulation response, and measured result is obtained under normal incidence.

Based on the scattering cancellation technique, an approach is proposed to improve the mantle cloak’s performance for electrically large cylinders. The procedure is based on the observation that th...

In this article, an exponential tapered Vivaldi antenna is designed. A ZIM (Zero Index Metamaterial) is introduced into the antenna to enhance its gain in whole of the ultrawideband. The proposed structure is covering the ultrawideband of 3.1-10.6 GHz as specified by FCC. The antenna has a bandwidth of 8.2GHz for the range 2.93- 11.13GHz. After introduction of metamaterial in the antenna, the gain of the antenna is enhanced in whole of the ultrawideband whereas maximum enhancement in the gain is 2.22dB at 10.6GHz. The proposed antenna also has low cross polarization less than -30dB for all the frequencies.