NISCAIR Online Periodicals Repository Collection: IJRSP Vol.38(5) [October 2009]

Development of microstrip array antenna for wide band and multiband applications

Mon, 28 Sep 2009 22:58:59 GMT

Title: Development of microstrip array antenna for wide band and multiband applications

Authors: Mallikarjun, S L; Madhuri, R G; Malipatil, S A; Hadalgi, P M

Abstract: The paper presents the design and development of an X-band linearly polarized microstrip array antenna. The array elements are fed by corporate feed network, which improves the impedance bandwidth of the two element rectangular microstrip array antenna (2RMSAA) by 15.38%. By increasing the array elements from two to four and eight, multiband operation can be achieved with improved impedance bandwidth. These multiband array antennas may provide an alternative to large bandwidth planar antennas in applications where large bandwidth is needed for operating at two separate transmit-receiver frequencies. When the two operating frequencies are far apart, a multiband antenna can be used to avoid the use of separate antennas. Experimental results for the array antennas in term of return loss, radiation pattern, -3dB beam width, and gain are presented

Page(s): 289-294

ANN technique for the evaluation of soil moisture over bare and vegetated fields from microwave radiometer data

Mon, 28 Sep 2009 22:58:59 GMT

Title: ANN technique for the evaluation of soil moisture over bare and vegetated fields from microwave radiometer data

Authors: Dharanibai, G; Alex, Z C

Abstract: Retrieving information from remotely sensed data is an important task. In the present work, data of L band microwave radiometer has been used to collect the brightness temperature over bare and vegetated fields in two polarizations at different moisture levels. Artificial neural network (ANN) trained with Levenberg-Marquardt algorithm has been used to determine soil moisture from brightness temperatures measured by microwave radiometry. ANN are trained to evaluate the moisture content in the range 0 - 36% from different sets of data of bare and vegetated fields. Properly trained feed-forward neural network with Levenberg-Marquardt algorithm predicted soil moisture content with less mean absolute error

Page(s): 283-288

Reduction of number of parameters and forecasting convective developments at Kolkata (22.53ºN, 88.33ºE), India during pre-monsoon season: An application of multivariate techniques

Mon, 28 Sep 2009 22:58:59 GMT

Title: Reduction of number of parameters and forecasting convective developments at Kolkata (22.53ºN, 88.33ºE), India during pre-monsoon season: An application of multivariate techniques

Authors: Chatterjee, Subhra; Ghosh, S; De, U K

Abstract: The present work aims at the formation of a statistical index using the most effective parameters out of primarily selected 20 parameters to predict the convective development at Kolkata (22.53ºN, 88.33ºE), India during the pre-monsoon season along with a multivariate statistical analysis of 20 different thermodynamic and dynamic parameters. In the first phase, linear discriminant functions formed with the help of linear discriminant analysis (LDA) of 20 parameters derived from the radiosonde observations at 0000 and 1200 hrs GMT during 1985-1996 at Kolkata produced 42.8 and 72.7% correct prediction for fair weather and convective development in next 12 hrs for the years 1997 to 1999 whereas in the evening the respective correct results are 50.8 and 56.6%. In the second phase, an attempt has been made to reduce the number of parameters using eigenvector analysis and correlation study between 20 original parameters and significant principal components. Here, again LDA has been performed with the parameters thus selected. The study reveals that for morning and afternoon, the number of parameters can be reduced to 6 and 7, respectively. The accuracy of predictions is also found to improve as compared to the first phase. However, it may be mentioned that total number of days involved in the present study is much less than the total number of days in the entire pre-monsoon season from 1985 to 1999 due to the unavailability of basic data needed to compute the required parameters

Page(s): 275-282

Ionospheric time delay variations in the equatorial anomaly region during low solar activity using GPS

Mon, 28 Sep 2009 22:58:59 GMT

Title: Ionospheric time delay variations in the equatorial anomaly region during low solar activity using GPS

Authors: Bhattacharya, Soumi; Purohit, P K; Gwal, A K

Abstract: Ionosphere can be a greatest variable source of error in precise time transfer using GPS satellites. The proposed navigation concept requires that a user measures the time-delay that satellite emitted signals experience in traversing the distance between satellite and user. The difference between the apparent range and the true range, or the free space velocity and the true velocity, is the quantity of interest. This quantity is directly proportional to the total electron content along the path of propagating signal. Thus, if the total electron content is known or is measured, a perfect correction to ranging could be performed. The equatorial anomaly region, Bhopal (geographic latitude. 23.2ºN, longitude 77.6°E), India with dual frequency from the GSV4004A GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver have demonstrated a high degree of accuracy in measuring the ionospheric group delay. The diurnal and seasonal variations of ionospheric time delay have been studied during the solar minimum period January to December 2005. It was found that diurnal variation of ionospheric time delay is maximum in the month of April and minimum in the month of December. The study reveals that during low solar activity, equinox season shows the maximum delay while summer gives the moderate and winter shows the minimum delay. The ionospheric time delay was also studied during magnetic storm conditions for the same period and the occurrence of daily maximum ionospheric time delay as a function of day during this period

Page(s): 266-274