Kumar Vaibhav Srivastava

A Compact Microstrip-Fed Triple Band-Notched UWB Monopole Antenna

In this letter, a novel low-profile microstrip-fed compact triple band-notched ultrawideband (UWB) antenna is proposed. Notch bands around the 3.3-3.8-GHz WiMAX and 5.15-5.85-GHz WLAN frequencies are obtained by etching out two elliptic single complementary split-ring resonators (ESCSRRs) of different dimensions from the radiating patch of the antenna. Furthermore, by placing two rectangular split-ring resonators near the feedline-patch junction of the antenna, rejection for the 7.9-8.4-GHz X-band frequencies is achieved. Design guidelines for implementing the notch-bands at the desired frequency regions are provided. The match between the simulated and experimental results suggests that the proposed antenna can be a good candidate for application in UWB communication systems.

Triple band polarization-independent metamaterial absorber with bandwidth enhancement at X-band

In this paper, we propose a triple band polarization-independent metamaterial absorber using square-shaped closed ring resonators over wide angle of incidence. The unit cell consisting of various square loops is designed by using the parametric analysis so that it exhibits a triple band absorption response with two bands lying in C-band and one in X-band for airborne and surveillance radar signal absorption applications. Furthermore, in X-band, the absorber exhibits a broadband response with full width at half maxima bandwidth of 940 MHz (9.43%). The structure exhibits bandwidth enhanced properties for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence up to 60°. The proposed structure is fabricated and experimental results show proper matching with the simulated responses.

Bandwidth-enhanced polarization-insensitive microwave metamaterial absorber and its equivalent circuit model

In this paper, a bandwidth-enhanced polarization-insensitive ultra-thin metamaterial absorber has been presented. A simple equivalent circuit model has been proposed describing the absorption phenomenon to estimate the frequency of absorption of the proposed microwave absorber. The basic structure consists of concentric rings embedded one inside another to enhance bandwidth by incorporating the scalability property of the metamaterials. Simulation results show that the structure has enhanced bandwidth response with full width at half maxima (FWHM) of 1.15 GHz (9.40–10.55 GHz) with two absorption peaks at 9.66 and 10.26 GHz (96% and 92.5% absorptivity, respectively). The structure is symmetric in design giving rise to polarization-insensitivity and can achieve high absorption for oblique incidence up to 40°. The proposed absorber has been fabricated and measured in anechoic chamber, showing that experimental results agree well with the simulated responses.

Triple band polarization-independent ultra-thin metamaterial absorber using electric field-driven LC resonator

In this paper, a triple band polarization-independent metamaterial absorber using electric field-driven LC resonators is proposed over wide angle of incidence. The unit cell is designed by parametric optimization in such a way that triple band absorption occurs in C-band. The proposed structure exhibits triple band absorption property for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence upto 60° for both TE and TM polarizations. The proposed structure is also fabricated and experimental results provide good agreement with the simulated responses. The constitutive electromagnetic parameters viz. effective permittivity and effective permeability are extracted from the simulated response, which support the absorption phenomena at all these three frequencies. The reflection from the structure is numerically computed and verified with simulated response, and it shows good agreement between them.

An Equivalent Circuit Model of FSS-Based Metamaterial Absorber Using Coupled Line Theory

An equivalent circuit model of an ultra-thin metamaterial absorber comprising a square-ring-shaped frequency selective surface (FSS) is presented. The model can be considered as series RLC resonators connected in parallel with coupling capacitance and short-circuited transmission line. The even- and odd-mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half-maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated, and close matching among the calculated, simulated, and measured results has been observed.

An Ultrawideband Ultrathin Metamaterial Absorber Based on Circular Split Rings

A simple design model for making ultrawideband ultrathin metamaterial absorber has been presented in microwave frequency regime. The proposed structure is composed of two concentric circular split rings imprinted on a metal-backed dielectric substrate. A 10-dB absorption bandwidth from 7.85 to 12.25 GHz covering the entire X-band has been observed in numerical simulation under normal incidence. The absorptivities of the proposed structure have been investigated under different polarization angles as well as oblique incidence. The electromagnetic field distributions and surface current plots have been illustrated to analyze the absorption mechanism of the proposed structure. The proposed absorber has been fabricated and its performance is experimentally verified at different angles of incidence and polarizations of incident electromagnetic wave. The designed absorber is compact, ultrathin (only λ0/15 thick corresponding to center frequency) and provides an alternative to construct broadband absorber for many potential applications.

Broadband Substrate Integrated Waveguide Cavity-Backed Bow-Tie Slot Antenna

A novel design technique for broadband substrate integrated waveguide cavity-backed slot antenna is demonstrated in this letter. Instead of using a conventional narrow rectangular slot, a bow-tie-shaped slot is implemented to get broader bandwidth performance. The modification of the slot shape helps to induce strong loading effect in the cavity and generates two closely spaced hybrid modes that help to get a broadband response. The slot antenna incorporates thin cavity backing (height <;0.03λ0 ) in a single substrate and thus retains low-profile planar configuration while showing unidirectional radiation characteristics with moderate gain. A fabricated prototype is also presented that shows a bandwidth of 1.03 GHz (9.4%), a gain of 3.7 dBi over the bandwidth, 15 dB front-to-back ratio, and cross-polarization level below -18 dB.

Wideband Ring Dielectric Resonator Antenna With Annular-Shaped Microstrip Feed

In this letter, an annular shape microstrip feed is presented, which has been used to excite a hybrid mode in ring dielectric resonator antenna. The proposed feed for ring dielectric resonator antenna has been achieved 10 dB impedance bandwidth of 66.72% at the center frequency of 5.35 GHz. The operating frequency range of the antenna is 3.49 GHz – 7.20 GHz. The radiation patterns are consistent throughout the operational bandwidth. A stable average measured gain of about 4.31 dB has been obtained over the operating band, which is suitable for wideband wireless system applications. A prototype is fabricated and measured. The simulated and measured results are in good agreement.

CRLH Unit-Cell Loaded Multiband Printed Dipole Antenna

In this letter, a conventional single-band printed dipole antenna is loaded with via-less composite right/left-handed (CRLH) unit cells to achieve multiband operation. Symmetrical loading of the unit cells provides a dual-band operation, while the asymmetrical loading of unit cells provides a triple-band operation. The new operational frequencies are lower compared to the resonance frequency of a reference dipole antenna and are controlled by the unit-cell parameters. The radiation patterns at all the operating frequencies of the proposed antennas are omnidirectional. Both the dual- and triple-band prototypes of CRLH loaded dipoles are fabricated to validate the results obtained in simulation. The results of measurements and electromagnetic (EM) simulations are in good agreement.

Dual-Band Circularly Polarized Cavity-Backed Crossed-Dipole Antennas

In this letter, a novel dual-band circularly polarized cavity-backed crossed-dipole antenna is proposed. Complementary split-ring resonators (CSRRs) are loaded along both the arms of double-sided printed crossed dipoles along with vacant quarter-printed rings to achieve dual-band circularly polarized operation. Cavity-backed reflector is employed in the antenna to achieve unidirectional pattern with high front-to-back-lobe ratio ( > 25 dB), wide circularly polarized radiation beamwidth, and high gain in both frequency bands. The impedance and axial-ratio bandwidths in both bands are also considerably improved by the cavity backing. The proposed dual-band crossed-dipole antenna has two operating bands centered at 1.81 GHz (impedance bandwidth 22.4%, axial-ratio bandwidth 6.6%) and 2.67 GHz (impedance bandwidth 33%, axial-ratio bandwidth 10.1%), respectively .