Gain Enhancement of a Wide Slot Antenna Using a Second-Order Bandpass Frequency Selective Surface

Gain enhancement of a wide slot antenna over a wide frequency band using a low profile, second order bandpass frequency selective surface (FSS) as a superstrate is presented in this paper. The proposed multilayered FSS with non-resonant unit cells in each layer allows in-phase transmission of waves radiated from the antenna over a 3dB bandwidth of about 50%. The design allows an enhancement of upto 4dBi in the antenna gain over the entire frequency band (5-8GHz) of operation. The FSS provides a very low insertion loss between the two transmission poles along with a linearly decreasing transmission phase over the band. The composite structure shows an impedance bandwidth (-10dB) of 65% with an average gain between 6-8dBi over the frequency band with a peak gain of 9dBi. Measurement results of the fabricated prototype matches well with the predicted values

Modeling of Modified Split-Ring Type Defected Ground Structure and Its Application as Bandstop Filter

The shape of a popular split-ring defected ground structure (DGS) is modified by selecting different width of the sides with respect to microstrip line. The frequency characteristics of proposed DGS unit show an attenuation zero close to the attenuation pole frequency. The unit cell is modeled by 3rd order elliptical lowpass filter and an equivalent circuit is presented accordingly. For proposed DGS, both pole and zero frequencies are obtained at lower values compared to split-ring DGS unit with uniform width. The variation of the width of the sides, parallel to microstrip line influences pole frequency. Two DGS cells with different pole frequencies cascaded under High-Low microstrip line realize a sharp and deep bandstop filter. Three-cascaded cells underneath a highlow impedance microstrip line produce sharper and wider bandstop filter characteristics

A Dual Layer Frequency Selective Surface Reflector for Wideband Applications

A dual-layer, bandstop frequency selective surface (FSS) is presented in this paper for wideband applications. Each layer uses patch type FSS with slots for miniaturization and are cascaded with an air gap in between. The low-profile FSS with unit cell dimension on the order of 0.2λ0×0.2λ0 provides transmission coefficient below -10dB in the frequency range of 4-7 GHz with 56% bandwidth. The FSS exhibits a nearly linear phase variation with frequency in the operating band and can be used as a substrate below planar wide band antennas with bi-directional radiation for enhancing its gain, directivity in the broadside direction as well as shielding it against nearby conductive surfaces such as metal cases, other printed antennas. Detailed design method, equivalent circuit analysis and measurement results of the FSS are presented in this paper

Target Detection: Remote Sensing Techniques for Defence Applications

The tremendous development in remote sensing technology in the recent past has opened up new challenges in defence applications. On important area of such applications is in target detection. This paper describes both classical and newly developed approaches to detect the targets by using remotely-sensed digital images. The classical approach includes statistical classification methods and image processing techniques. The new approach deals with a relatively new sensor technology, namely, synthetic aperture radar (SAR) systems and fast developing tools, like neural networks and multisource data integration for analysis and interpretation. With SAR images, it is possible to detect targets or features of a target that is otherwise not possible. Neural networks and multisource data integration tools also have a great potential in analysing and interpreting remote sensing data for target detection

Comparison of hot-electron transmission in ferromagnetic Ni on epitaxial and polycrystalline Schottky interfaces

The hot-electron attenuation length in Ni is measured as a function of energy across two different Schottky interfaces viz. a polycrystalline Si(111)/Au and an epitaxial Si(111)/NiSi_2 interface using ballistic electron emission microscopy (BEEM). For similarly prepared Si(111) substrates and identical Ni thickness, the BEEM transmission is found to be lower for the polycrystalline interface than for the epitaxial interface. However, in both cases, the hot-electron attenuation length in Ni is found to be the same. This is elucidated by the temperature-independent inelastic scattering, transmission probabilities across the Schottky interface, and scattering at dissimilar interfaces.Comment: 5 pages, 5 figure

Filtering DRA Array and Its Applications in MIMO for Sub-6 GHz Band

A dielectric resonator-based filtering array antenna along with multi input - multi output (MIMO) characteristics is represented in this paper. Two rectangular dielectric resonators, together with a filtering power splitter (PS) is used to get a high gain filtering response. The PS, which consists of a simple T-junction 3-dB power splitters and two pairs of band-rejection resonators, provides four transmission zeros outside the passband. Detail study with an equivalent circuit is presented to understand the working principle of the filtering PS. By utilizing this PS, a two element DRA array is designed at sub-6 GHz frequency band (3.20 GHz-3.54 GHz) with an average broadside gain of 7.8 dBi in the passband and four radiation dips outside the passband. The proposed filtering DRA array effectively suppresses the out-of-band signal, delivers sharp selectivity at band edges. Finally, coalescing the two-filtering array, a MIMO antenna system is presented here. The filtering array MIMO antenna gives reasonable port isolation of greater than 20 dB throughout the operating band. All the major diversity parameters to establish MIMO characteristics e.g. envelop correlation coefficient (ECC), diversity gain (DG), channel loss capacity (CCL), and total reflection coefficient (TARC) persists within their tolerable ranges

Spin communication over 30 μ\mum long channels of chemical vapor deposited graphene on SiO2_2

We demonstrate a high-yield fabrication of non-local spin valve devices with room-temperature spin lifetimes of up to 3 ns and spin relaxation lengths as long as 9 $\mu$m in platinum-based chemical vapor deposition (Pt-CVD) synthesized single-layer graphene on SiO$_2$/Si substrates. The spin-lifetime systematically presents a marked minimum at the charge neutrality point, as typically observed in pristine exfoliated graphene. However, by studying the carrier density dependence beyond n ~ 5 x 10$^{12}$ cm$^{-2}$, via electrostatic gating, it is found that the spin lifetime reaches a maximum and then starts decreasing, a behavior that is reminiscent of that predicted when the spin-relaxation is driven by spin-orbit interaction. The spin lifetimes and relaxation lengths compare well with state-of-the-art results using exfoliated graphene on SiO$_2$/Si, being a factor two-to-three larger than the best values reported at room temperature using the same substrate. As a result, the spin signal can be readily measured across 30 $\mu$m long graphene channels. These observations indicate that Pt-CVD graphene is a promising material for large-scale spin-based logic-in-memory applications

A High Gain Dual Notch Compact UWB Antenna with Minimal Dispersion for Ground Penetrating Radar Application

A compact (27.5×16.5×0.8 mm3) co-planar waveguide fed printed ultra-wideband antenna operating in the impedance band of 1.75-10.3 GHz with two wide frequency notch bands at 2.2–3.9 GHz and 5.1–6 GHz, is introduced. Dual notch is achieved by inserting U-slot on the radiator and with inverted patch shaped downscaled parasitic load at the opposite end of feed line. Maximum antenna gain augmentation by about 5 dBi is achieved without changing the bandwidth, by incorporating a dual layer reflective frequency selective surface (FSS) of dimension 33×33×1.6 mm3 below the antenna. The antenna-FSS composite structure exhibits maximum radiation in the broadside direction with a peak gain of 9 dBi and an average radiation efficiency of more than 80% in the operating band. Antenna transfer function and group delay are experimentally studied in ground coupling mode of ground penetrating radar (GPR). Linear magnitude response of transfer function and consistent, flat group delay are achieved, that ensure minimal antenna dispersion and its ability for GPR application

A Compact Umbrella-Shaped UWB Antenna with Gain Augmentation Using Frequency Selective Surface

A compact (35 mm × 30 mm × 0.8 mm) co-planar waveguide fed ultra-wideband antenna with bended ground plane suitable for GPR applications is proposed in this article. The umbrella shaped radiating element is constructed using the intersection of two ellipses. The proposed antenna provides a wide impedance bandwidth of 10.35 GHz (3.05–13.4 GHz) covering the unlicensed UWB band. The simply structured antenna is easy to fabricate and to integrate in PCB board. A frequency selective surface (FSS) with two layers, each of 4×4 array, cascaded via air gap, is incorporated in the antenna as a substrate to enhance the gain by 2 to 4 dBi over the entire frequency band. Metamaterial inspired unit cells are chosen for the FSS layers, with unit cell dimension on the order of λ/10 with respect to 3 GHz, much less than λ/4. The spacing between the antenna and FSS is kept so as to enhance the gain value without hampering nearly flat gain response over the band. The gain is maintained between 5.5–8.5 dBi over the band. The antenna was investigated by comparing the simulated and measured fundamental antenna parameters. High radiation efficiency of more than 90% with non-varying group delay and nearly omnidirectional H-plane radiation pattern were achieved. Measurement results validated the antenna performance and gain enhancement due to the addition of FSS layers