NISCAIR Online Periodicals Repository Collection: IJRSP Vol.41(1) [February 2012]

Return loss improvement of power splitter on EBG

Sun, 29 Jan 2012 22:58:59 GMT

Title: Return loss improvement of power splitter on EBG

Authors: Mukherjee, Biswajeet

Abstract: In the present paper, the improvement of the return loss of a power splitter/ divider, designed by partial removal of electromagnetic band gap (EBG) rods, has been investigated. The EBG used is a rod structure and shows a band gap in the range 2.2395 - 2.5774 GHz. The power splitter has a return loss of 2.45 GHz which falls in the range of the band gap. It has been found that a larger matrix of the EBG structure is needed in order to improve the return loss significantly. However, the removal of rods, as the matrix size is increased, needs to be done with a fixed ratio of the input feed length to coupling length in order to maintain the same resonant frequency. The improvement in the return loss has been significant from -19.932 dB (for a 5×5 matrix) to -37.214 dB (for a 17×17 matrix).

Page(s): 58-61

Prediction of annual and seasonal soil temperature variation using artificial neural network

Sun, 29 Jan 2012 22:58:59 GMT

Title: Prediction of annual and seasonal soil temperature variation using artificial neural network

Authors: Jebamalar, A S; Raja, S Abraham Thambi; Bai, S Jeslin Sunitha

Abstract: The back propagation algorithm, an artificial neural network (ANN) training algorithm, is a widely applied mathematical implementation for spatial monitoring and is used in the present study for the analysis and prediction of soil temperature. The soil temperature data at 10 and 20 cm soil depths were collected from the Agricultural College and Research Institute, Killikulam, Tuticorin District of Tamil Nadu. The observed values during the year 2004 at 10 and 20 cm soil depths were plotted to understand the annual and seasonal behaviour of the temperature wave. The wave characteristics such as range of soil temperature and rate of change of temperature/week were estimated and tabulated. Data for 1993 – 1997 (5 years) and 1993 – 2002 (10 years) were separately used as inputs for the prediction of soil temperature in 2004 using ANN. The predicted values were compared with the observed values and statistically validated. The characteristics of predicted annual and seasonal wave were also compared with observed values. It was found that the predicted values of annual wave fitted well with observed ones with little variation for the seasonal waves. The range of soil temperature for predicted values coincided almost with the observed ones with regard to the annual and the seasonal waves for both 10 and 20 cm soil depths. The rate of change of temperature/week of the predicted values coincided well with the observed ones for 10 cm soil depth. For 20 cm soil depth, the predicted values deviated from the observed ones for the winter season while the annual and pre-monsoon seasonal waves coincided well with the observed values. The surface temperature was also predicted independently from 10 and 20 cm soil temperature and error validation was done. From these, it may be convincingly stated that the ANN can be used as a good mathematical model for the prediction of soil temperature.

Page(s): 48-57

Pc4 Occurrence and its dependence on Kp values at low latitudes in India

Sun, 29 Jan 2012 22:58:59 GMT

Title: Pc4 Occurrence and its dependence on Kp values at low latitudes in India

Authors: Ansari, I A; Khan, M T

Abstract: A study has been undertaken for Pc4 geomagnetic pulsations ( in 6.7 – 22.2 mHz frequency range) at three very low latitude stations, viz. Pondicherry (PON) (geomagnetic latitude 2.5ºN, geomagnetic longitude 151.97ºE), Nagpur (NAG) (geomagnetic latitude 11.72ºN, geomagnetic longitude 151.93ºE), Hanle (HAN) (geomagnetic latitude 23.38ºN, geomagnetic longitude 151.89ºE) in India employing three axis fluxgate magnetometers, established and operated by the Indian Institute of Geomagnetism (IIG), Navi Mumbai. Digital dynamic spectra (DDS) for the north-south (X), east-west (Y) and vertical (Z) components of the recorded data were constructed for each day for one year (1 January to 31 December 2005). The X and Y components of these DDS were investigated for carrying out statistical study of the dependence of diurnal and seasonal variations of occurrence of Pc4 events on Kp.

The monthly variation of Pc4 occurrence has a Kp dependence range from 0 to 9-. However, the yearly Pc4 occurrence was found to be evenly distributed with magnetic activity over Kp range from 2- to 4 at all the three stations with the peak occurrence recorded at Kp = 3-. The magnitudes of durations of Pc4 occurrence decreased in the station order PON, HAN and NAG, respectively. The prominent peaks in the seasonal Pc4 occurrence were observed at Kp = 3-, 3 for all the seasons. However, additional peaks were observed at Kp = 1-, 1 and 1+ for the autumn season. It is also worth noting that Pc4 in winter was observed during intense magnetic activity when 5+ < Kp < 8+.

Page(s): 39-47

Diurnal and seasonal variations in sporadic E-layer (Es layer) occurrences over equatorial, low and mid latitude stations - A comparative study

Sun, 29 Jan 2012 22:58:59 GMT

Title: Diurnal and seasonal variations in sporadic E-layer (Es layer) occurrences over equatorial, low and mid latitude stations - A comparative study

Authors: Prasad, S N V S; Prasad, D S V V D; Venkatesh, K; Niranjan, K; Rao, P V S Rama

Abstract: The simultaneous hourly ionograms, from an equatorial station Trivandrum (8.47°N, 76.91°E), a low latitude station Waltair (17.70N, 83.3°E) in the Indian sector and a mid latitude station Kokubunji (35.7°N, 139.5°E) in the Japanese sector during the high sunspot year 2001, are scaled for the study of E-region parameters, namely the virtual height of sporadic E-layer (h’Es) and the critical frequency of sporadic E-layer (foEs). The diurnal, seasonal and day-to-day variations in h’Es and foEs are studied for all the three stations. It is observed that the sporadic E-layer is absent in the early morning and post sunset hours over Trivandrum during three different seasons. The values of h’Es are more at Kokubunji as compared to those at equatorial (Trivandrum) and low latitude (Waltair) stations during the three different seasons. The critical frequency of sporadic E-layer (foEs) over Trivandrum shows higher values, compared to those over Waltair and Kokubunji during daytime hours, in three different seasons indicating that foEs decrease as the latitude increases. The seasonal variation in foEs shows higher values during daytime hours of equinox and winter months over equator (Trivandrum) compared to those over low (Waltair) and mid (Kokubunji) latitude stations. The variations in h’Es and foEs for quiet and disturbed conditions indicate that the h’Es variation during quiet days of equinoctial months at Kokubunji shows a primary peak around morning hours while it is absent at Waltair and Trivandrum. Further, the behaviour of blanketing frequency of Es layer fbEs, and foEs-fbEs are also studied.

Page(s): 26-38