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Rao P.H.,Center for Electromagnetics
2010 International Conference on Wireless Communication and Sensor Computing, ICWCSC 2010 | Year: 2010

Cognitive radio is a new concept that utilizes the spectrum efficiently by shifting the frequency bands with time and availability. This puts a challenge on the antenna design to meet the demands of cognitive radio. This paper reviews the possible antenna configurations like wideband antennas, polarization and frequency reconfigurable antennas. Whilst there are many possible ways in which such systems could be configured, few possible antenna configurations are discussed and some design approaches are outlined. ©2010 IEEE.

Rao P.H.,Center for Electromagnetics | Swaminathan M.,Georgia Institute of Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2011

A compact reduced unit cell size electromagnetic bandgap (EBG) power plane, realized with a combination of alternating impedance EBG and multiple narrow slits, is presented. By concatenating 2 2 high-frequency unit cells, a virtual low-frequency EBG unit cell is synthesized without changing the overall dimensions. In this configuration, the basic slit in the high-frequency unit cell remained same, and an additional slit with longer dimensions is added in parallel to the basic slit by synthesizing a larger low-frequency unit cell. EBG is characterized for its dispersion diagram, noise suppression, signal integrity, and electromagnetic radiation. Fabricated EBG exhibits a bandgap from 0.9 to 3.5GHz with isolation better than 40 dB over the band. Radiated emission of the new EBG is small with an average value of 35 dBuV/m. Compact EBG also exhibits low impedance, which is less than 1 over the stopband. Eye patterns are generated to analyze signal integrity issues when the data lines are referenced over the solid ground plane and EBG plane. The degradation of the maximum eye opening and the maximum eye width for the proposed EBG power plane at 2 Gb/s data rate is about 17.8 and 1, respectively, with reference to the equivalent board with solid power plane. © 2006 IEEE.

Arunachalam S.,Applied Technology Internet | Ramamoorthi P.,Center for Electromagnetics | Gunasekaran S.,CSIR - Central Electrochemical Research Institute
Proceedings of the Indian National Science Academy | Year: 2014

A few commercial publishers dominate provision of access to scientific and technical information sought after by researchers around the world. Increasing subscription prices of journals at rates higher than general inflation caused librarians to think of forming consortia, but publishers started selling online journals as bundles, and libraries ended up with many journals their researchers have very little use for. Scientists and librarians adopted open access, but publishers came up with hybrid journals and article processing charges to beat any adverse effect on their profits caused by the fast-spreading open access movement. We compare the steps taken by scientists and librarians in the West to reclaim ease of access to research findings with what is happening in India. We end with a few suggestions.

George Thomas K.,Center for Electromagnetics | Praveen G.,Center for Electromagnetics
IEEE Transactions on Antennas and Propagation | Year: 2012

A circularly polarized printed antenna, capable of operating over an octave bandwidth is designed and fabricated. The design is evolved from classical printed monopole/dipole geometry. It employs a microstrip-line fed rectangular radiator, printed on the top of a substrate. The ground, extended as another rectangular radiator is printed on the bottom of the substrate. Both the top and bottom radiators are asymmetrically configured in such a way that the surface currents on them are orthogonal so as to produce left-hand circular polarization (LHCP). The antenna configuration is simulated using a commercially available EM solver. The simulated and measured results closely match within the operating bandwidth. The measured results show a-10-dB return loss bandwidth of 800 MHz to 4.15 GHz and a 3-dB axial ratio bandwidth of 1.5 GHz to 3.4 GHz. For the designed center frequency of 2.45 GHz, these correspond to 136% and 77% respectively. A parametric study of the design is carried out and the mechanism of circular polarization is described. © 2012 IEEE.

Thomas K.G.,Center for Electromagnetics | Sreenivasan M.,Center for Electromagnetics
IEEE Transactions on Antennas and Propagation | Year: 2010

A compact planar ultrawideband (UWB) antenna with band notched characteristics is presented. Modification in the shape of radiation element and ground plane with two symmetrical bevel slots on the lower edge of the radiation element and on the upper edge of the ground plane makes the antenna different from the rectangular printed monopole. These slots improve the input impedance bandwidth and the high frequency radiation characteristics. With this design, the reflection coefficient is lower than 10 dB in the 3.1-10.6 GHz frequency range and radiation pattern is similar to dipole antenna. With the inclusion of an additional small radiation patch, a frequency-notched antenna is also designed and good out of band performance from 5.0-6.0 GHz can be achieved. Measured results confirm that the antenna is suitable for UWB applications due to its compact size and high performance. Also an approximate empirical expression to calculate the lowest resonant frequency is proposed. © 2009 IEEE.

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