Dipak L. Sengupta

Radiation characteristics of a spherical array of circularly polarized elements

The radiation properties of a spherical phased-array antenna with circularly polarized elements are studied. Each antenna element is assumed to have a cosine type of field pattern. It is found that such an array is capable of providing complete hemispherical coverage without appreciable loss of gain. The radiation produced by the array stays circularly polarized in all directions, and the state of polarization is independent of beam steering. A special distribution of elements on a spherical surface is developed. This considerably suppresses the grating lobes in the pattern and thereby makes the antenna array broadband. Numerical calculations are made to determine the directivity and half-power beamwidth for the radiation patterns produced under various situations.

Theory of dielectric-filled edge-slot antennas

A theory has been developed for dielectric-filled edge-slot (DFES) antennas which belong to a class of circumferential slot antennas that are suitable for conformal mounting on conducting bodies of revolution. The specific antenna considered consists of a disk of dielectric substrate mounted between the two halves of a conducting cylinder and is excited at its center by a coaxial stub. It can be tuned for a desired operating frequency with the help of a number of axially oriented passive metallic posts located inside the dielectric region. For analysis, the antenna is modeled as a symmetrically excited E -type radial waveguide loaded with the metallic posts and terminated by an equivalent admittance appropriate for the radiating aperture. Circuit parameters for the metallic posts in the radial waveguide are obtained by detailed field analysis using mode matchng techniques. These are then used, along with the equivalent transmission line circuit for the antenna, to obtain the input reflection coefficient as a function of frequency for various DFES antennas. The results of computations based on the theory developed are compared with available measured values.

Electromagnetic interference from wind turbines

Summary form only given. During the late nineteen seventies and eighties the University of Michigan Radiation Laboratory, under sponsorship from the US Department of Energy, studied theoretically and experimentally the effects of wind turbines (WTs) on the performance of various electromagnetic systems. The article summarizes selected portions of the fundamental work carried out and techniques developed under the program which are now routinely used throughout the world for such interference measurements and analyses. To a receiver of electromagnetic signals in the vicinity of a WT, the rotating blades act as a time varying multipath source. As a result of the scattering from the blades the total signals received are generally amplitude and phase (or frequency) modulated. The former being more dominant for slow moving WTs. These extraneous modulations of the desired signal, if sufficiently strong, can adversely affect the performance of an electromagnetic system. The degree and nature of the interference will depend on the signal transmission and reception methods used by the system, and the electromagnetic scattering characteristics of the WT blades. Wide-ranging theoretical and experimental investigation of the electromagnetic effects of large WTs on the performance of TV and FM broadcast reception, microwave link and variety of navigation systems were carried out. The WT interference effects on TV reception were studied most extensively.

Transmission Line Model Analysis of Rectangular Patch Antennas

ABSTRACT The transmission line model has been utilized to determine the input performance of a rectangular patch antenna excited by a coaxial probe. Approximate expressions have been developed for the resonant propagation constant (or the resonant frequency), quality factor and input resistance of such antennas which clearly indicate the effects of the various antenna parameters including the feed on these quantities under dynamic conditions. The results of computations based on the expressions developed are compared with available measured values. The present work establishes the transmisson line model as a valid representation of rectangular patch antennas, and would facilitate the design of such antennas without elaborate numerical computation. The model has also been applied to determine the resonant parameters for a similar antenna tuned by passive metallic posts. Validity of an approximate expression derived for the resonant frequencies of such tunable antennas has also been established by compariso...

Investigation of the parasitic loop counterpoise antenna

The radiation field produced by a parasitic loop counterpoise antenna is investigated. This is a new antenna configuration which consists of a small circular loop in the presence of a large parasitic loop and is placed above a circular ground plane or counterpoise. Geometrical theory of diffraction is applied to obtain the theoretical expressions for the far field produced by such an antenna. Within the range of approximation the agreement between theory and experiment has been found to be very good. The introduction of a parasitic loop, in general, reduces the ground plane edge diffraction effects on the far-field patterns and makes the overall pattern in the half-plane above the counterpoise less directional. Possible application of the antenna is also discussed.

An appreciation of J.C. Bose's pioneering work in millimeter waves

The pioneering work in the area of millimeter waves, performed by J. C. Bose, a physicist from Calcutta, India, during 1894-1900, is reviewed and appraised. Various measurement techniques and circuit components, developed by him a hundred years ago, are still being used. The development of the electromagnetic horn, the point-contact detector, and the galena (semiconductor) detector of electromagnetic waves are attributed to the original research of J.C. Bose.

Centennial of the semiconductor diode detector

J.C. Bose, a physicist from India, developed a semiconductor receiver for the detection of millimeter waves (60 GHz) during 1894-1896. Interestingly, Boses galena receiver, for which he received a patent (application filed September 30, 1901, issued March 29, 1904), is the forerunner of semiconductor diode detectors. This paper reviews the pioneering work of Bose in the area of millimeter waves and appraises the circumstances leading to the development and construction of such a device.

Experimental study of a spherical array of circularly polarized elements

The radiation properties of a simple spherical phased array of 16 flat spiral antennas have been investigated experimentally over a frequency range of 0.6 GHz to 3 GHz. The results obtained indicate that such an array is capable of operating with widely spaced antenna elements. The spherical array surface considerably reduces the grating lobe amplitudes in the pattern, thereby making the array broad-band. The polarization characteristics of the radiation field were also studied.

Who Was James Clerk Maxwell and What Was and Is His Electromagnetic Theory

The electromagnetics community makes profuse utilization of Maxwells equations, his theory, and their applications. It is arguable that very few of us have clear ideas about what exactly Maxwell did and what kind of scientist he was. In fact, he developed many of the fundamental ideas in electrical engineering, and provided mathematical language for their exposition. His contributions to other branches of science are no less significant. He was not only one of the great scientists of the nineteenth century, but was also great for all time. To this end, the present essay starts with a brief outline of his life. It then provides a short but critical discussion of his original contributions in electromagnetics and their evolution as his electromagnetic theory. We also give a cursory review of his significant contributions in other areas of science. It is hoped that this will provide the electromagnetics-community readers with a better and more complete appreciation of James Clerk Maxwell as a scientist, as well as of his electromagnetic theory as we know now it.

Rudimentary horn antenna

Preliminary results obtained from an investigation of the impedance and radiation properties of a novel broadband linearly polarized antenna called the rudimentary horn are reported. When properly designed the antenna is found to be capable of maintaining its desirable radiation and impedance characteristics over a 10:1 band of frequencies.