Ayyangar R. Harish

Analysis of low range Indoor Location Tracking techniques using Passive UHF RFID tags

The problem of indoor position location tracking has been addressed in this paper, using passive UHF RFID tags. The test area is first calibrated by placing some reference tags at known positions and orientations. This data obtained by measuring the detection powers for these reference tags is later used to train an algorithm, which is in turn used to predict unknown tag positions. The results obtained have been discussed.

A Modified Bow-Tie Antenna for Dual Band Applications

A modified bow-tie antenna fed by a 50-Omega paired strip transmission line is proposed for dual band applications. A printed bow-tie antenna is modified by incorporating triangular shaped parasitic elements. A procedure to design an antenna that works at two arbitrary frequencies f 01 and f 02 is discussed. It is observed that the higher resonance frequency can be as high as three times the lower resonance frequency. The measured radiation patterns are nearly omnidirectional. The simulated results are in good agreement with the measured results.

A Modified Wideband Dipole Antenna for an Airborne VHF Ice-Penetrating Radar

A 15-element wideband dipole antenna array was developed for operation with the Multichannel Coherent Radar Depth Sounder/Imager on board the National Aeronautics and Space Administration P-3B aircraft. The array, aligned in the cross-track direction, was designed for applying digital beam forming and direction of arrival estimation algorithms to improve clutter suppression and for 3-D imaging of ice sheets. The antenna array is embedded inside an aerodynamic fairing structure designed for airborne operation. While the fairing meets all the structural and aircraft requirements, initial measurements performed on the original prototype array revealed the adverse impact of the fairing structure on antenna performance. The materials used for the construction of the fairing produced electrical loading effects on the radiating structure, which adversely impacted the bandwidth and return loss characteristics of individual antenna elements. This paper describes a set of modifications to the original antenna design based on computer simulations and laboratory measurements, aimed at optimizing antenna return loss and bandwidth while reducing mutual coupling. The final antenna and fairing structure achieved a fractional bandwidth of 40% at a center frequency of 195 MHz with a demonstrated peak power handling capability of 150 W. We were able to reduce the mutual coupling between antenna elements by a factor of two through modification of the dipole ends.

Analysis of UHF passive RFID tag behavior and study of their applications in low range indoor location tracking

New techniques are being devised to use RFID technology to enable Indoor Position tracking of tagged objects. RFID holds immense promise in this area as tags are cheaply available and robust to various kinds of RF interference. In this paper, passive UHF (868MHz) tags placed at uniformly spaced points in a grid in different sets of orientations are used to find out the contour patterns of reader antenna in a given area under static environment. This information is used to estimate the position of unknown tags from the readings obtained by the reader antennas. The computed results are presented and discussed.

A direct method to compute the coupling between nonidentical microwave cavities

A new technique to compute the coupling, as a function of frequency, between nonidentical resonators is presented in this paper. The structure is separated by introducing electric and magnetic wall boundary conditions on the plane of separation, and coupling coefficient is computed directly from the eigenvalues of the four individual structures. The proposed technique has been used to compute the coupling between coaxial combline resonators. It is found to be computationally much faster than the iterative technique. The computed results are in good agreement with the measured results.

Printed wideband variable strip width loop antenna

A printed wide band loop antenna having variable strip width is presented. The antenna is fed by a 50 Omega balanced parallel strip transmission line. Based on the parametric study of the antenna, it is shown that the optimum performance of the antenna, in terms of impedance bandwidth for -10 dB input reflection coefficient | Sn|, is achieved only when the ratio of the inner diameter to outer diameter of the loop is nearly 0.6. Impedance bandwidth of the order of 50% makes it suitable applications like mobile communication, direction finding, wireless LAN, GPS- PCS, ISM bands etc. Measured and simulated results of a prototype antenna are compared.

A broadband dipole on a double layered via-less High Impedance Surface

A low profile double layered via-less High Impedance Surface (HIS) is proposed and tested with conventional bow-tie dipole antenna kept in close proximity (~0.005λ). A stable radiation pattern has been achieved with impedance bandwidth of 11.55% and a gain of 6 dBi throughout the band. Proposed HIS is better than the single layered HIS in terms of bandwidth and gain.

Orientation Detection Using Passive UHF RFID Technology [Education Column]

A simple, compact, rechargeable handheld radio-frequency identification (RFID) reader was designed to detect the orientation of tagged objects. The system uses a linearly polarized reader antenna and the orientation sensor of the mobile device to identify the orientation of the tag. The system works in the ultra-high-frequency (UHF) RFID band. Detailed testing was done in different surroundings with various materials and tags. The system was able to correctly identify the orientation in several cases with an average angular error of less than 10°. This system can also be used to demonstrate the concept of polarization.

A direct method to compute the coupling between non-identical microwave cavities

A new technique to compute the coupling between non-identical resonators has been presented in this paper. The proposed technique has been used to compute the coupling between coaxial combline resonators coupled magnetically. The proposed technique has been found to be computationally much faster than the traditional iterative technique. The computed results have been found to be in good agreement with the measured results.

Studies on application of fractal based geometries in printed antenna structures

Several novel antenna structures based on a combination of regular and fractal shaped elements are presented. It has been shown with case studies that the performance of the antennas can be optimized by judicious choice of fractal geometries. Though the fractal elements have a high degree of regularity, introduction of certain irregularities in the structures can result in improved performance of the antennas. Both directly coupled and parasitically coupled fractal elements have been used to construct these novel antenna structures.