Total visitors: 45  since 25-05-05

Indian Journal of Radio & Space Physics

 

 

 

ISSN : 0367-8393

 

       CODEN : IJRSAK

VOLUME 34

NUMBER 2

APRIL 2005

 

 

CONTENTS

 

Editorial: Radio science in Asia-Pacific region

89

A P Mitra*

 

 

A theoretical explanation of intensity of low latitude ELF emissions and identification of their generation mechanism

91

Ram Prakash*, D D Gupta & A P Singh

 

 

Analytical study of whistler mode instability with parallel AC field by Lorentzian Kappa

98

R S Pandey, R P Pandey, A K Srivastav* & Kiran Dubey

 

 

Absolute and convective instability study of weakly compressible mixing layers

106

A P Roychowdhury*

 

 

Effect of solar parameters on Antarctic, Arctic and tropical ozone during the last solar cycle

114

P K Jana* & S C Nandi

 

 

Statistical morphology of cloud occurrences and cloud attenuation over Hyderabad, India

119

S K Sarkar*, Iqbal Ahmad & M M Gupta

 

 

Theoretical analysis of linear array antenna of stacked patches

125

Vijay K Pandey & Babau R Visvakarma*

 

 

Parametric study of temperature sensitivity for microstrip patch antenna

131

Surendra Kumar Roy*, Santosh Kumar Jha & Lalan Jha

 

 

Effect of dielectric and conducting corner reflectors on V-slot waveguide antenna

135

B S Makal, R M Vani, P M Hadalgi, S N Mulgi & P V Hunagund*

 

 

Effects of tuning stub on microstrip patch antenna

139

Surendra Kumar Roy & Lalan Jha*

 

 

________

 

*Corresponding authors

 

 

Indian Journal of Radio & Space Physics

Vol. 34, April 2005, pp. 91-97

 

A theoretical explanation of intensity of low latitude ELF emissions and identification of their generation mechanism

Ram Prakash, D D Gupta & A P Singh

 

The intensities of low latitude ELF hiss emissions are calculated for known plasma parameters by considering incoherent Cerenkov emission mechanism and electron cyclotron resonance instability mechanism. The equatorial intensities calculated in incoherent Cerenkov emission mechanism at L = 1.30-5.50, being several orders of magnitude lower than the observed intensities, rule out the possibility of generation of low latitude ELF hiss emissions in this mechanism. Unlike this, the intensities calculated by electron cyclotron resonance instability mechanism at the equatorial locations above L = 4 are found to be consistent with the intensities observed in the low latitude ground stations. Therefore, it is opined that these emissions originate in the electron cyclotron resonance instability mechanism above L = 4 in the equatorial plane. However, it has been shown that the ELF hiss band below 1 kHz propagates from the generation region in the vicinity of the plasmapause to low latitudes after several successive magnetospheric reflections there, confirming the suggestion of Hayakawa et al. [J Atmos & Terr Phys, 37 (1975) 517; Planet & Space Sci, 25 (1977) 35].

 

Keyword: ELF emissions, Cerenkov emission, Resonance instability, Magnetospheric reflections

PACS No: 94.30Tz; 94.30.Gm; 94.20.Pp

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, April 2005, pp. 98-105

 

Analytical study of whistler mode instability with parallel AC field by Lorentzian Kappa

R S Pandey*, R P Pandey, A K Srivastav & Kiran Dubey

 

In the present paper whistler mode instabilities have been analysed for an anisotropic plasma having a generalized Lorentzian (Kappa) distribution function with a spectral index k, reducible to Maxwellian distribution in the limit k®¥, in the presence of parallel AC field by method of characteristics solution. Using details of particle trajectories, dispersion relation and growth rate have been evaluated for plasma parameters suited to Earth’s magnetosphere. Results have been discussed and compared with that obtained by earlier workers using Maxwellian distribution. It is observed that the Maxwellian and Kappa distributions differ substantially in the high energy tail, but the differences become less significant as k increases.

 

Keywords: Whistler instability, Lorentzian Kappa

PACS No: 52.35 Hr, 94.30 Tz

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, April 2005, pp. 106-113

 

Absolute and convective instability study of weakly compressible mixing layers

A P Roychowdhury

 

This is an analysis of stability study of weakly compressible mixing layers under non-homentropic flow conditions. The condition of non-zero group velocity required for convective instability analysis was seen to give new findings as stated below. Also, the dispersion relationships are functions of the cross-stream derivatives, Mach number and chemical reaction parameters. Three modes of oscillations for developing mixing layer were chosen based on previous findings of the author and later in this work their possible validity were confirmed as follows. Jet mode (Mode 1), mixed mode (Mode II) and fully developed mixing layer mode (Mode III) oscillations for developing mixing layers are considered in this study. Using impulse response technique it is seen that for symmetric temperature profile, Mode I is absolutely unstable, Mode II is both convectively and absolutely unstable, partially each, and Mode III is dominantly convectively unstable with pockets of absolute instability. For the asymmetric temperature profile of T = 1+ l tanh (y), Mode I is weakly convectively unstable, Mode II is weakly absolutely unstable and Mode III is convectively unstable for major regions of the flow.

 

Keywords: Absolute instability, Convective instability, Mixing layers, Non-isentropic formulation

PACS No: 44.25 +f; 47.27 Te

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 34, April 2005, pp. 114-118

 

Effect of solar parameters on Antarctic, Arctic and tropical ozone during the last solar cycle

P K Jana & S C Nandi

 

A critical analysis has been made on the variations of Antarctic, Arctic and tropical ozone and different solar parameters during the last solar cycle. It has been observed that yearly variations of ozone concentrations at Halley Bay (76°S, 27°W), a British Antarctic survey station, at Sodankyla (67.4°N, 26.6°E), an Arctic survey station and at Ahmedabad (23°N, 72.6°E), an Indian survey station are identical to that of August, April and March concentrations, respectively. The yearly variations of solar flare numbers and solar uv-fluxes are identical to that of October values, but relative sunspot numbers and solar flare index are identical to that of April values. The correlation coefficients between ozone concentrations and different solar parameters are not so significant. It is also concluded that the intense yearly decrease of Antarctic and Arctic ozone concentrations from year to year during springtime is independent of solar parameters.

 

Key words: Ozone depletion, Solar activity, Antarctic ozone, Arctic ozone, Tropical ozone

PACS No: 92.60.e, 96.60.Rd, 82.40.we, 94.10 Fa

 

 

 

Indian Journal of Radio & Space Physics

Vol. 34, April 2005, pp. 119-124

 

Statistical morphology of cloud occurrences and cloud attenuation over Hyderabad, India

S K Sarkar, Iqbal Ahmad & M M Gupta

 

Attenuation due to clouds in millimeter wave and microwave frequency bands lead to degradation in the performance of radio communication, especially for low noise systems. Frequent presence of cloud causes some amount of link degradation for significant percentage of time over the tropical Indian subcontinent. The cloud morphology particularly in relation to radio wave propagation over different geographical region of India is very essential and important. In view of this, systematic studies on cloud occurrence morphology over different geographical locations in India have been undertaken. Based on low level cloud coverage observations, frequency of cloud occurrences over Hyderabad (17.27°N, 78.28°E), situated in Indian tropical southern region in different months during daytime and nighttime has been deduced and presented in this paper. The low-level cloud over Hyderabad has been found to occur for many days and nights and particularly in the months of June-September. The low level cloud occurrences are minimum in winter months. The specific attenuation of radiowave due to clouds at various frequencies ~10, 20, 30, 40, 50, 75 and 100 GHz for summer and monsoon seasons has also been deduced. The specific attenuation of radio wave due to cloud at 30 GHz for liquid water content ~1 g/m3 is found to be 0.88 dB/km, while at 75 GHz the specific attenuation is ~5.55 dB/km.

 

Keywords: Cloud occurrence, Attenuation, Microwave attenuation, mm wave attenuation

PACS No: 92.60 Nv; 84.40. _x

 

 

 

Indian Journal of Radio & Space Physics

 Vol. 34, April 2005, pp. 125-130

  

Theoretical analysis of linear array antenna of stacked patches

Vijay K Pandey & Babau R Vishvakarma

 

A linear four-element stacked array antenna is analyzed. It is observed that stacked element array antenna shows marked improvement in the bandwidth and gain over the single-element array antenna. The bandwidth of the stacked antenna array improves to 14.8% over the 4% bandwidth of the single-element array antenna, whereas the radiated power is enhanced by 0.82 dB as compared to the single-element array antenna. It is further observed that the resonance frequency, gain and directivity are highly dependent on the thickness and permittivity of the upper substrate.

 

Keywords: Array antenna, Stacked patch antenna, Microstrip patch antenna

PACS No.: 84.40.Ua

IP Code: H01Q9/00; H01Q21/00; H01Q23/00

 

 

 

Indian Journal of Radio Space Physics

Vol. 34, April, 2005, pp. 131-134

 

Parametric study of temperature sensitivity for microstrip patch antenna

Surendra Kumar Roy1, Santosh Kumar Jha2 & Lalan Jha1

 

Microstrip substrates were exposed to large temperature variations and their temperature dependent properties were measured. A parametric study of the temperature sensitivity for circular microstrip patch antenna utilising a substrate with a lower dielectric constant and thermal coefficient is found to be less sensitive to the temperature variations.

 

Key words: Environmental conditions, Microstrip patch antenna, Temperature sensitivity

PACS No.: 84.40 Ba

IPC Code: H01Q9/00; H01Q21/00; H01Q23/00

 

 

 

Indian Journal of Radio Space Physics

Vol. 34, April, 2005, pp. 135-138

 

Effect of dielectric and conducting corner reflectors on V-slot waveguide antenna*

B S Makal & R M Vani and P M Hadalgi, S N Mulgi & P V Hunagund

 

This paper presents the effect of dielectric and conducting material corner reflectors (CRs) on the antenna parameters of V-slot waveguide antenna (V-SWGA). The beam is sharpened only at optimum angle (q) and position (d) of CR from V-SWGA. The conducting material is more effective than the dielectric material CR in sharpening the beam of V-SWGA.

 

Keywords: Slotted waveguide antenna, Corner reflector

PACS No.: 84. 40Ba

IPC Code: H01Q9/00; H01Q21/00; H 01Q23/00

 

 

Indian Journal of Radio & Space Physics

 Vol. 34, April 2005, pp. 139-141

 

Effects of tuning stub on microstrip patch antenna

Surendra Kumar Roy & Lalan Jha

 

Use of tuning stubs to trim the phase of a microstrip feed line or to tune the resonant frequency of a microstrip patch antenna is discussed in this paper. The variation of resonant frequency with stub-length of microstrip patch antenna is also discussed. The experimental results regarding phase shift and resonant frequency with stub-length are in good agreement with the theoretical results.

 

Key words: Tunning stub, Microstrip patch antenna, Resonant frequency

PACS No.: 84.40 Ba

IPC Code: H01Q-9/00; H01Q-21/00; H01Q-23/00