Defence Electronic Research Laboratory

Hyderabad, India

Defence Electronic Research Laboratory

Hyderabad, India
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Kumar A.,Defence Electronic Research Laboratory | Ahirwar S.D.,Defence Electronic Research Laboratory | Sairam C.,Defence Electronic Research Laboratory | Sarma A.D.,Osmania University
Progress in Electromagnetics Research Letters | Year: 2013

The design approach and development of a right hand circularly polarized wideband microstrip antenna for multi- constellation Global Navigation Satellite System (GNSS) is presented. The antenna is corner truncated square patch, parasitically excited by a dielectric covered straight probe. A thermacol layer of thickness λ=14 at center frequency is used to support the microstrip over the ground plane substrate. The simulated and measured results are presented. The antenna shows wide beam radiation patterns with axial ratio less than ±1 dB. Its VSWR is better than 2.8: 1 and the gain varies from 1.2 dBi to 3.5 dBi over the frequency band.

Kamatham Y.,ACE Engineering College | Sarma A.,Osmania University | Kumar A.,Defence Electronic Research Laboratory | Satyanarayana K.,Osmania University
IETE Journal of Research | Year: 2013

Multipath is one of the prominent error sources in Global Positioning System (GPS), which adversely affects the accuracy of the user′s position. This paper describes the estimation of frequency components of multipath error signal using spectral analysis and its effective mitigation using time-varying digital filters. Four types of 2 nd order filters, namely, Butterworth, Type I and II Chebyshev and Elliptic filters, are examined for mitigation of multipath and their performance is compared. It is observed that by applying digital filters of different cut-off frequencies over the spectrum of the multipath, one can significantly reduce the multipath errors. The designed filters are applied to GPS data acquired from a typical urban environment site and found that Butterworth filter reduced the error most effectively. To extract the magnitude of error contribution in low and medium multipath frequency ranges, its mitigation is carried out with Butterworth filter. The performance of the filter is validated by the spectral analysis for multipath signals before and after filtering process. However, this spectral analysis followed by digital filtering is different from the approaches reported elsewhere in the open literature. This new approach is very useful in identifying least-affecting multipath sites for GPS applications. Copyright © 2013 by the IETE.

Kumar A.,Defence Electronic Research Laboratory | Sarma A.D.,Osmania University | Mondal A.K.,Defence Electronic Research Laboratory | Yedukondalu K.,Bhoj Reddy Engineering College for Women
Progress In Electromagnetics Research M | Year: 2010

Local Area Augmentation System (LAAS) based on multi-constellation GNSS can provide improved accuracy, availability and integrity needed to support all weather category II and III precision approach landing of aircraft. In order to receive satellite signals of GNSS, an antenna working over wide frequency band and high phase center stability is preferred. Commonly used antennas like crossed dipoles, patch etc. are inherently narrow band. This paper describes the design and development of half-cardioid shaped dual arm, wide band printed circuit antenna. The antenna has low VSWR of < 3:1, a stable phase center and good right hand circularly polarized radiation patterns covering full L-band frequencies. The simulated and measured results compare well. This compact antenna can also be used on ground, ship and airborne platforms to receive signals from multiple GNSS satellites above the horizon.

Yedukondalu K.,Bhoj Reddy Engineering College for Women | Sarma A.D.,Osmania University | Kumar A.,Defence Electronic Research Laboratory
IEEE Asia-Pacific Conference on Circuits and Systems, Proceedings, APCCAS | Year: 2010

Positional accuracy of GPS is limited by various error sources like ionosphere, troposphere, clock, instrumental bias, multipath etc. Among these, multipath errors are quite significant, since it should be dynamically modelled with respect to GPS receiver environment. In this paper, multipath error is estimated based on both code and carrier phase measurements using CMC (code minus carrier) method. It is verified with experimental static dual frequency GPS receiver data. The multipath time series data is applied to various Recursive Least Squares (RLS) adaptive filtering algorithms to minimize the multipath error. The results are encouraging and significant reduction of multipath error is observed. The convergence of RLS filters is faster than the conventional Least Mean Squares (LMS) adaptive filters. These RLS filters can also be applied to real time kinematic GPS applications. © 2010 IEEE.

Sairam C.,Defence Electronic Research Laboratory | Khumanthem T.,Defence Electronic Research Laboratory | Ahirwar S.,Defence Electronic Research Laboratory | Singh S.,Defence Electronic Research Laboratory
Proceedings - 2011 Annual IEEE India Conference: Engineering Sustainable Solutions, INDICON-2011 | Year: 2011

In this paper, design and development of broadband blade antenna covering 0.5-2.0 GHz is presented. Blade monopole antennas are preferred for airborne application due to their compact size, light weight and aerodynamic shape leading to minimum drag. For lower air drag, the antenna is placed inside the aerodynamically shaped radome. An air core coil is also provided for DC grounding proposes. The antenna configuration is first optimized using FDTD based CST Microwave Studio TM EM simulation software and latter practically implemented. The comparison of simulated and measured results is also presented in this paper. © 2011 IEEE.

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