Communication Systems Group

Bangalore, India

Communication Systems Group

Bangalore, India
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Guha D.,University of Calcutta | Banerjee A.,University of Calcutta | Kumar C.,Communication Systems Group
IEEE Transactions on Antennas and Propagation | Year: 2012

A resonant mode (HEM 12δ), other than those (HEM 11δ and TM 01δ) conventionally excited and used in a cylindrical dielectric resonator antenna (CDRA) has been examined with a view for using it as another radiating mode with broadside radiation patterns. Excitation of the mode, being the most challenging aspect, has been discussed and resolved by employing an innovative technique. The proposed concept has been successfully verified and experimentally demonstrated for the first time. More than 8-dBi peak gain with excellent broadside radiation has been obtained from a prototype shaped from a commercially available low-loss dielectric material with relative permittivity 10. © 2006 IEEE.


Kumar C.,Communication Systems Group | Guha D.,University of Calcutta
IEEE Transactions on Antennas and Propagation | Year: 2012

Experiments with probe-fed circular patches using conventional and defected ground planes flashed some interesting features relating to cross-polarized (XP) electric fields and associated radiations before the present authors. Those led to a series of new investigations for understanding the nature of XP fields and to deal with them using defected ground structure (DGS) for improved XP performance. In the first phase of investigation, the XP radiations of a probe-fed circular patch with conventional ground plane have been critically studied as a function of the radial probe location. Remarkably significant effect is experimentally demonstrated. New information about orthogonal resonant fields and its importance in designing an antenna is provided. In the second phase of investigation, limitations of dot-shaped DGS in reducing XP level are experimentally studied. As its improved variants, two new DGS geometries such as annular ring and circular arcs have been explored. The arc-DGS appears to be highly efficient in terms of suppressing XP fields. Suppression by 10-12 dB has been experimentally demonstrated. Each design has been experimented in both C- and X-bands to earn confidence on the measured data. © 2006 IEEE.


Guha D.,University of Calcutta | Banerjee A.,University of Calcutta | Kumar C.,Communication Systems Group | Antar Y.M.M.,Royal Military College of Canada
IEEE Antennas and Wireless Propagation Letters | Year: 2014

Higher-order {\rm HEM}12 \deltamode has been experimentally realized in a cylindrical dielectric resonator antenna (CDRA) very recently revealing broadside radiation like the dominant {\rm HEM}11 \deltamode. The primary challenge is the excitation of the mode in a practical DRA sitting on a metal ground plane, which was first resolved by introducing a floating feed as an equivalent current ribbon. In this letter, yet another technique has been explored using a conventional probe-fed CDRA placed on a metal plate. Only a new trough-shaped air cavity has been introduced in the ground plane just beneath the DRA to simulate a special boundary condition, which enunciates desired modal fields. Such a technique may be improvised for other potential applications. The proposed concept has been verified using both simulated and experimental results. © 2002-2011 IEEE.


Guha D.,University of Calcutta | Gajera H.,University of Calcutta | Kumar C.,Communication Systems Group
IEEE Transactions on Antennas and Propagation | Year: 2015

In this communication, cross-polarized (XP) radiation of cylindrical dielectric resonator antenna (CDRA) has been investigated with a view to identify the source of the same. The study starts with a conjecture, which has been established through a systematic study using simulated results. The inference has been verified experimentally with the help of a set of prototypes. HEM21δ has been identified as the XP generating mode and a small metallic grounded post of circular cross section has been conceived to perturb the same to prove the conjecture. This insight has been extended to demonstrate a practical application indicating a possibility of achieving up to 8-10-dB suppression in XP radiation from a CDRA. © 1963-2012 IEEE.


Kumar C.,Communication Systems Group | Guha D.,University of Calcutta
IET Microwaves, Antennas and Propagation | Year: 2014

Defected ground structure (DGS)-integrated rectangular microstrip patch has been experimentally investigated with an aim to improve polarisation purity in radiated fields. Width to length ratio (aspect ratio) of a patch attributes different characteristic features. Therefore present experimental studies have been executed for four different aspect ratio values like 1.6, 1.3, 1.0 and 0.8. Folded defects have been employed in H-plane. Possibility of achieving high polarisation purity (over 25 dB isolation between co- to cross-polarised fields) with improved impedance bandwidth has been demonstrated. The variation in XP fields as a function of the patch aspect ratio has been investigated and a strong physical insight into the modal fields with and without DGS has been developed. © The Institution of Engineering and Technology 2014.


Biswas S.,Institute of Technology and Marine Engineering | Guha D.,University of Calcutta | Kumar C.,Communication Systems Group
IEEE Transactions on Antennas and Propagation | Year: 2013

Controlling higher order modes up to third harmonic of the fundamental operating frequency in a microstrip line-fed patch antenna has been successfully demonstrated. Harmonic rejection in the antenna has been achieved at its feed level using highly compact design of defected ground structure (DGS). Rejection characteristics have been improved adding an open stub to the feed line. All possible higher order modes occurring in between the fundamental and the 3rd harmonic have been identified. Relative suppression of radiated fields with and without DGS-control has been quantitatively measured and effective control of harmonics has been experimentally ensured. The area occupied by the proposed DGS has been compared with earlier designs and over 40-90% reduction in size has been documented. © 2013 IEEE.


Kumar C.,Communication Systems Group | Srinivasan V.V.,Communication Systems Group | Lakshmeesha V.K.,Communication Systems Group | Pal S.,Communication Systems Group
IEEE Transactions on Antennas and Propagation | Year: 2010

A novel design of dielectric rod antenna is presented here. Compared to the conventionally used tapered dielectric antennas, this configuration is capable of producing higher gain for a given length of the antenna. The design of an antenna using the new configuration having a gain of 16.7 dBi at 5.6 GHz is discussed. The length of this antenna is 2.3 λ0, which is considerably less compared to the conventional design. The material used for the antenna is Teflon. Along with the detail simulated results, the measured results of the fabricated prototype antenna are also presented. © 2006 IEEE.


Picu A.,Communication Systems Group | Spyropoulos T.,Communication Systems Group
Proceedings of the Annual International Conference on Mobile Computing and Networking, MOBICOM | Year: 2010

Opportunistic Networking allows wireless nodes to exchange data and information of interest with peers in communication range. These nodes form a large, dynamic, multi-hop network "on the fly". Challenging optimization problems arise, such as end-to-end routing, resource allocation (e.g., for buffer space and bandwidth), content placement etc., exacerbated by the lack of end-to-end connectivity. While globally optimal solutions are normally sought in network optimization, node actions and decisions in this context are inherently local. As a result, most solutions proposed rely on local heuristics without any guarantees about their convergence properties towards a desired global outcome. In this paper, we argue that the framework of Markov Chain Monte Carlo (MCMC) optimization can be applied to many problems in Opportunistic Networking, providing efficient local algorithms that provably converge to a globally optimal solution. As a case study, we use the problem of optimal relay selection for group communication (e.g., multicast), based on node contact patterns.


Kumar C.,Communication Systems Group | Kumar V.S.,Communication Systems Group | Srinivasan V.V.,Communication Systems Group
IEEE Transactions on Antennas and Propagation | Year: 2013

Monopulse tracking using multiple horns is an attractive and low-cost option for a ground station feed. In this paper, a compact design of this type of feed operating in dual band is discussed. This design uses dielectric rod elements as radiators. Four elements in 2 × 2 array configuration operate for downlink reception and tracking application. One single element with high gain at the center of the array operates for uplink using high power. This allows some design flexibility with respect to independence in configuring the two chains and also provides some inbuilt isolation between them. However, there are issues in this configuration with respect to the mutual coupling between the elements. These are addressed in detail and an optimum design with measured results of a tracking feed operating in 3.4 to 4.2 GHz for downlink and 6.3 to 6.8 GHz for uplink for an 11-m diameter dual shaped Cassegrain antenna is presented here. © 1963-2012 IEEE.


Kumar C.,Communication Systems Group | Kumar B.P.,Communication Systems Group | Kumar V.S.,Communication Systems Group | Srinivasan V.V.,Communication Systems Group
IEEE Transactions on Antennas and Propagation | Year: 2013

Design aspects of an active spherical phased-array antenna (SPAA) operating in dual circularly polarized (CP) mode are discussed here. Dual CP configuration with good cross-polarized isolation enables frequency reuse using polarization diversity. This design also implements sharing of the resources like amplifiers and phase shifters in an optimal way to reduce mass, power requirement, and cost of the antenna. The antenna is hemispherical in shape and maintains required effective isotropic radiated power (EIRP) over a hemispherical coverage area. Detailed analysis including the effect of failure of a few of the elements of the array and the measured results of the antenna at X-band are discussed here. This antenna has been used for transmission of payload data from a low Earth orbit satellite of ISRO. © 2012 IEEE.

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