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Pune, India

Khatavkar N.,Indian Institute of Technology BHU Varanasi | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2016

Encompassment of radar communication in modern avionics provides the backbone for safe flight and tactical warfare. In the past few decades radar technology has achieved commendable precision and sophistication, but efficient communication relies upon effective transmission of electromagnetic waves through materials shielding the antenna and exhibiting high transparency for radio/microwaves. Since the structure of radomes in supersonic aircraft is dominated by aerodynamic standards, numerous challenges are encountered while selecting the materials apposite for construction having superior mechanical strength and resilience while displaying the minimum influence on the transmission profile of radio waves. The radome structure of aircrafts is subjected to sudden acceleration, drag forces and erosion due to rain and dust, which change the transmission characteristics due to change in shape/thickness of the structure. The problems are further complicated by the advent of supersonic/hypersonic aircrafts and missiles where high strength preservation and structural integrity is necessary at temperatures in excess of 350 °C. This review systematically throws light on the composite materials and existing technologies employed for the fabrication of high strength, low dielectric loss sandwich radomes for supersonic aircrafts. © The Royal Society of Chemistry 2016. Source

Krishna R.V.S.R.,DIAT DU | Kumar R.,ARDE
Journal of Electromagnetic Waves and Applications | Year: 2016

A V-shape slot antenna for dual slant polarization is proposed. The slot is the union of two stepped rectangular slots tilted at ±45° with the vertical. Each section of the slot is excited using a microstrip feed line printed on the other side of the substrate. The feed is also stepped and bent so as to cross the slot at right angles. The decoupling between the ports is provided by means of narrow rectangular stubs placed at the intersection of the slot arms. Measurements taken on the fabricated prototype indicate an impedance bandwidth from 3.3 to 12 GHz with isolation better than 15 dB across the band. The aperture electric field distributions as well as far field radiation patterns are used to verify the dual slant polarization achieved with the antenna. The time domain characterization of the antenna is done by calculating the fidelity factor which is found to be >0.75 indicating suitability of the antenna for pulse transmission. For determining the diversity behavior, the envelope correlation coefficient is calculated and found to be below 0.004. The antenna has a peak gain from 4 to 6 dBi. A modified design of the antenna is also presented with impedance bandwidth from 3 to 12 GHz and isolation better than 20 dB from 3.7 GHz onwards. With compact features and wideband return loss and isolation, the antennas are expected to be useful for diversity applications in ultra wideband communication devices such as MIMO wifi, imaging radars, and polarimetric sensing devices. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source

Kushwaha N.,DIAT DU | Kumar R.,ARDE
IET Microwaves, Antennas and Propagation | Year: 2015

In this study, a new compact coplanar waveguide-fed wideband circularly polarised slot antenna is designed and fabricated. To achieve circular polarisation, the slot in the ground plane is truncated at one corner and excited by a modified L-shaped radiating element. To achieve wide axial ratio bandwidth (ARBW), one end of the L-shaped patch is connected with the ground via a slit. The ARBW is further improved by properly placing two additional narrow slots in the ground plane. The measured impedance bandwidth and ARBW at boresight are achieved 87.2% (from 2.2 to 5.6 GHz) and 81.05% (from 2.2 to 5.2 GHz), respectively. For the better understanding, the surface current distribution and parametric studies are presented. To characterise the antenna in the time domain, group delay and system fidelity factor (SFF) are measured. The measured group delay has less variation (of 0.5 ns) in the operating band and the measured SFF is found to be 0.89. The measured and simulated results are in good agreement. © 2015. The Institution of Engineering and Technology. Source

Kumar R.,ARDE | Naidu P.V.,Symbiosis International University | Kamble V.,DIAT DU
Progress In Electromagnetics Research B | Year: 2014

A compact, coplanar waveguide (CPW) fed asymmetric slot antenna with dual operating bands is proposed. The slot is modi-ed rectangular in shape and asymmetrically cut in the ground plane. A hexagonal patch fed by a two-step CPW is used to excite the slot. The feed itself is slightly asymmetric (shifted, with unequal ground planes). The asymmetric cuts on the slot together with the feed line asymmetry have helped in obtaining ultra wideband impedance matching. An extra resonance at 2.4 GHz for Bluetooth applications is obtained by cutting an additional meandered narrow rectangular shape slit in the ground plane. The prototype of the proposed antenna has been fabricated and tested. The measured 10 dB return loss bandwidth of the proposed antenna is 200MHz (2.3-2.5 GHz) for the -rst band and 12.1 GHz (2.9-15.0 GHz) for the second band. The radiation patterns of the proposed antenna are obtained and found to be Omni-directional in H-plane and bi-directional in E-plane. The measured and simulated results are in good agreement. Source

Thakur D.G.,DIAT DU | Ramamoorthy B.,Indian Institute of Technology Madras | Vijayaraghavan L.,Indian Institute of Technology Madras
International Journal of Advanced Manufacturing Technology | Year: 2012

The use of superalloy Inconel 718 is increasing in most of the sophisticated applications like aircraft engines, industrial gas turbines, rocket engines, space vehicles, submarines, etc. Hence, in-depth understanding of this material helps to determine the ability of this material to withstand severe conditions of stress, temperature, corrosion, and controls its longevity and reliability. In the present work, an attempt has been made to study the relationship of degree of work hardening and tool life as a function of cutting parameters like cutting speed, feed, depth of cut, untreated tungsten carbide and postcryogenic-treated tool. Work hardening and tool life are the major factors which need to be controlled/improved to enhance the machinability characteristics of superalloy Inconel 718. A significant performance in tool life was observed due to cryogenic treatment given to tungsten carbide tool. Moreover, it was observed that optimized cutting parameters not only minimized/controlled work hardening characteristics but also improved tool life while high-speed machining of Inconel 718. © Springer-Verlag London Limited 2011. Source

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