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A printed leaf shaped compact (40 mm × 30 mm × 0.8 mm) UWB antenna added with dual frequency selective surfaces (FSS) of dimension 44 mm × 44 mm × 1.6 mm is proposed. The FSS layers having 4 × 4 array in each can provide maximum gain of 8.7 dBi and gain enhancement by 2–4.5 dBi in the antenna bandwidth of 3–14.64 GHz. The proposed design also ensures maximum radiation in the broadside direction with average radiation efficiency of 85%. The antenna bandwidth and group delay responses were measured in close proximity of soil test bed for varying test bed thicknesses. Relative bandwidth of more than 114% with non‐varying group delay response ensure the ability of proposed antenna to work for ground coupling ground penetrating radar applications.

A compact (38.31 mm × 34.52 mm × 0.8 mm) leaf shaped CPW fed ultra‐wideband antenna is proposed. The antenna gives wide impedance bandwidth from 2.58 GHz to 11.62 GHz with sharp triple notch bands (3.28 GHz–3.82 GHz, 5.12 GHz–5.4 GHz, and 5.7 GHz–6 GHz) to eliminate interference from co‐existing IEEE 802.16 WiMAX (3.3 GHz–3.8 GHz), IEEE 802.11y (3.65 GHz–3.69 GHz), IEEE 802.11a WLAN (5.15 GHz–5.35 GHz and 5.725 GHz–5.825 GHz), and IEEE 802.11p DSRC (5.85 GHz–5.925 GHz) bands. The antenna provides minimal gain variation (2–5 dBi), flat group delay response and non‐varying transfer function with high average efficiency of 88% in the pass band. Significant drop in gain and efficiency, nonlinearity in transfer function, and high variation in group delay are observed at notch bands. Antenna VSWR, and efficiency are measured in close proximity of sand, wood, and glass. Satisfactory results ensure its ability to work as Ground penetrating radar antenna.

A compact (35 3 30 3 0.8 mm 3 ) umbrella shaped ultra wideband antenna that gives wide impedance bandwidth of more than 123% with low dispersion, 3-5 dBi gain and average efficiency of 84% is proposed. The antenna is tested in close proximity of soil. Satisfactory results ensure its ability to work as GPR antenna. K E Y W O R D Sground coupling, ground penetrating radar, ultra wide-band antenna, umbrella shape | I NT RODU CTI ONGround penetrating radar is widely used to scan the sub surface of interest by transmitting and receiving electromagnetic waves using UWB antenna. 1 Different types of UWB antenna like horn and Vivaldi, 2-6 valentine, 7 bow-tie, 8,9 rugby ball, 10 frequency independent, 11 and slot antenna 12,13 were proposed earlier for GPR applications. Horn, Vivaldi and Valentine antenna can provide satisfactory GPR performances but heavy weight and bulky structures limited their uses in GPR. Frequency independent like spiral antenna can provide wide bandwidth but it also introduce significant ringing effect. Bowtie, rugby ball antenna can be very compact in size and able to give good GPR performance but it require capacitive and inductive loading to broaden impedance bandwidth and minimize ringing effect, respectively. The loading increases antenna efficiency loss significantly. Also low gain profile is another drawback of such antenna. Slot type GPR antenna also has larger dimensions. Recently Ming Li et al. proposed a high gain, low dispersive slot 146 | KUNDU AND JANA antenna having dimension of 106 3 68 mm 2 and limited impedance bandwidth of 1.4-3.5 GHz. 13 Wide bandwidth is required to get better plan resolution of GPR. Plan or lateral resolution indicates the scanning ability to differentiate between any two buried objects of same depth. The relation between antenna bandwidth (B) and plan resolution length (Dr) is given by the expression, B ! V/4Dr where V indicates speed of electromagnetic wave in subsurface material.In this article, a compact, coplanar waveguide fed, umbrella shaped monopole antenna is proposed. The antenna gives a wide impedance bandwidth from 3.1 to 13.1 GHz covering the unlicensed 3.1-10.6 GHz UWB band as allotted by FCC in 2002. 14 Fundamental antenna parameters like VSWR, pattern, efficiency, gain, transfer function (S 21 ) and group delay were simulated and measured. Good agreement is observed in the results. The antenna is also tested in ground coupling mode to ensure its ability as GPR antenna. | A NTEN NA DE S I GNGeometry of the proposed antenna is shown in Figure 1. Figure 1A shows the construction of radiating patch by taking the intersection of two ellipses of radius (1.7R, R) and (1.5R, 2R), respectively. The maximum patch length is 2R and width is 3R. The maximum patch dimension (D), that is, maximum patch width is taken as k L /4 where k L 5 c/f L . Here, c indicates speed of light and f L represents lower cutoff frequency that is 3.1 GHz. Figure 1B,C represents the design flow. Design A and B indicate microstrip fed and coplanar fed antenna structure...

The work presents a comparative study on the effects of In incorporation in the channel layer of AlGaN/GaN type-II heterostructures grown on c-plane sapphire by Plasma Assisted Molecular Beam Epitaxy. The structural characterizations of these samples were performed by High-Resolution X-Ray Diffraction (HRXRD), X-ray Reflectivity (XRR), Field Emission Scanning Electron Microscopy, and High Resolution Transmission Electron Microscopy. The two-dimensional electron gas in the AlGaN/GaN and AlGaN/InGaN interface was analyzed by electrochemical capacitance voltage and compared with theoretical results based on self-consistent solution of Schördinger–Poisson equations. The carrier profile shows enhanced confinement in InGaN channel (1.4393 × 1013 cm−2 compared to 1.096 × 1013 cm−2 in GaN). On the basis of HRXRD measurements, the stress-strain of the layers was examined. The c- and a-lattice parameters of the epilayers as well as in-plane and out-of plane strains were determined from the ω-2θ for symmetric scan and ω-Xθ (X represents the coupling coefficient) for asymmetric scan. Strain, tilt, and correlation lengths were calculated from Williamson–Hall plots, whereas stress was examined from modified plot of the same data assuming Uniform Stress Deformation Model. Moreover, the twist angle was measured from skew symmetric scan of (102), (103), and (105) plane along with (002) symmetric plane. The composition and strain/relaxation state of the epilayers were observed in detail by reciprocal space mapping (RSM). The symmetric (002) triple axis RSM and asymmetric (105 and 114) double axis RSM of grazing incidence and exit geometry were carried out on each sample. The defect density was measured from HRXRD curves of skew symmetric (002) and (102) reflection plane. The Al and In mole fraction and strain states of the layers were calculated by fitting the experimental curves with computer simulations and compared with theoretical findings based on elastic theory. The thicknesses of the layers and roughness of the interfaces were measured from simulation of the nominal structure by fitting with XRR experimental curves. The HRXRD measured thicknesses of the layers were further confirmed by cross sectional electron micrographs.

A new co‐planar waveguide fed UWB antenna with transitions in feed line is proposed in this article. A good agreement is found in between simulated and measured results of the proposed design. The antenna provides a bandwidth improvement of more than 120% with min. group delay variation, high efficiency of 88%, and gain variation of 2–5 dBi. The antenna pattern is omnidirectional in H‐plane and monopole like in E‐plane. The proposed antenna is also tested in close proximity of soil to establish its ability for GPR applications.

In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al2O3) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10−3(1 × 10−3), and −1.7 × 10−3(2 × 10−3) in GaN layer and 5.1 × 10−3 (−3.3 × 10−3), and 8.8 × 10−3(−1.3 × 10−3) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum.

Influence of transferred-electron effect on drain-current characteristics of AlGaN/GaN heterostructure field-effect transistors J. Appl. Phys. 109, 024509 (2011); 10.1063/1.3533941 Deep level transient spectroscopy in plasma-assisted molecular beam epitaxy grown Al 0.2 Ga 0.8 N / GaN interface and the rapid thermal annealing effect