NOPR Collection:

A compact broadband gap-coupled microstrip antenna

Thu, 01 Apr 2004 00:00:00 GMT

Title: A compact broadband gap-coupled microstrip antenna Authors: Mulgi, S N; Vani, R M; Hunagund, P V; Hadalgi, P M Abstract: A method for improving the bandwidth of microstrip antenna by incorporating a common parasitic element, which is gap-coupled to the radiating edges of rectangular patches, is described. This technique makes the proposed antenna structure compact in size with a bandwidth of around 22%. The theoretical bandwidth and input impedance for the proposed configuration are also evaluated. Experimental and theoretical results are found to be in good agreement. Page(s): 139-141

Potential and field distribution inside an axially split cylinder

Thu, 01 Apr 2004 00:00:00 GMT

Title: Potential and field distribution inside an axially split cylinder Authors: Das, B N; Gayen, Arun Abstract: The paper presents a method of evaluation of potential and field distribution inside an axially split cylinder, one part of which is insulated and other maintained at ground potential. The Laplace's equation expressed in cylindrical polar coordinates is solved assuming no axial variation, and using boundary condition for the potential. The radial and angular components of the field intensity are found using the appropriate derivative operator in the cylindrical co-ordinate system. The condition under which the radial field is maximum, is derived in terms of angular widths of the conductors. If the radial field intensity exceeds the breakdown limit, the resulting breakdown of the gas leads to plasma generation inside the structure. Page(s): 130-138

Variability of dielectric constant of dry soil with its physical constituents at microwave frequencies and validation of the CVCG model

Thu, 01 Apr 2004 00:00:00 GMT

Title: Variability of dielectric constant of dry soil with its physical constituents at microwave frequencies and validation of the CVCG model Authors: Calla, O P N; Baruah, A; Das, B; Mishra, K P; Kalita, M; Haque, S S Abstract: In the designing of active and passive sensors for microwave remote sensing of soil, its electrical parameters like scattering coefficient and emissivity play a vital role. One of the important parameters on which these two depend is the value of the dielectric constant that again varies with the physical constituents of the soil. In this paper, an attempt has been made to study the variability of the dielectric constant of dry soil with its physical constituents. The soil samples are taken from different parts of northern India and variations of dielectric constant as observed in the X-band are presented here. The CVCG model, generated to compute the dielectric constant for dry soil from its physical constituents has also been validated. Page(s): 125-129

Integrated satellite microwave and infrared measurements of precipitation during a Bay of Bengal cyclone

Thu, 01 Apr 2004 00:00:00 GMT

Title: Integrated satellite microwave and infrared measurements of precipitation during a Bay of Bengal cyclone Authors: Gairola, R M; Varma, A K; Pokhrel, Samir; Agarwal, Vijay K Abstract: In the present paper, an approach for integrated IR and microwave measurements using various satellite sensors have been used for the study of a severe cyclone over Bay of Bengal and adjoining Eastern India and Bangladesh during 24-29 April 1991. The rain estimates from measurements of brightness temperatures from Special Sensor Microwave/Imager (SSM/I) and Outgoing Longwave Radiation (OLR) from IR radiances of polar orbiting and geostationary satellites have been used. Since the OLR derived rainfall exhibit a larger spatial spread with lower intensities in rain fall fields, we have followed the above procedure for optimally combining both the observations for more realistic rainfall o n regional scale to study precipitation fields. Since the OLR rains are well represented spatially and tempo rally by more frequent observations from both geostationary and polar orbiting satellites, the algorithm sharpens the IR derived rain s and augments it to the microwave derived rain. The combined IR and microwave rain algorithm brings out the finer details of the cyclone structure and precipitation fields, and thus seems to be highly promising for operational applications. Some aspects of the associated wind fields are also examined for their relationship with tropical rain intensity in the present case. A comparison of rainfall is performed with rare in-situ observations over the coastal regions during the severe cyclone. Page(s): 115-124