NOPR Collection:

Electronic scanning in linear active antenna array

2005-10-01T00:00:00Z

Title: Electronic scanning in linear active antenna array Authors: Pandey, Vijay K; Vishvakarma, Babau R Abstract: The beam scanning characteristics of 1×4 linear Gunn-integrated active antenna array are investigated by varying the bias voltages of the different elements in the array keeping the side lobe level at least 10 dB down the main beam level. The optimization of beam scanning by varying the bias voltage of all the four elements simultaneously exhibited a beam scanning of 40° with power deviation of 1.85 dB in main beam, which is better than the earlier reported data. Page(s): 357-362

Investigation of radiation properties of a right isosceles triangular microstrip antenna

2005-10-01T00:00:00Z

Title: Investigation of radiation properties of a right isosceles triangular microstrip antenna Authors: Tiwari, V K; Bhatnagar, D; Saini, J S; Kumar, P Abstract: Radiation properties of a probe fed linearly polarized right isosceles triangular microstrip antenna (RITMA) with single feed point are experimentally investigated in this paper. Radiation patterns, return loss, bandwidth and gain results obtained are compared with theoretical results. The theoretical analysis is carried out by applying cavity model based modal expansion technique. A fairly nice agreement between computed and measured results is recorded that validates the accuracy and utility of proposed technique for the analysis of RITMA geometry. Page(s): 353-356

A new whistler recorder and analyzer developed at Agra*

2005-10-01T00:00:00Z

Title: A new whistler recorder and analyzer developed at Agra* Authors: Singh, Vikram; Kumar, Manoj; Singh, Birbal Abstract: A new experimental set-up for recording and analysis of whistlers and VLF emissions has been developed at Agra, which is less expensive, automatic and time saving in comparison to earlier experimental set-up being used in different whistler stations in India. The new experimental set-up employs a crossed loop antenna, amplifiers, low pass filter, a sound card and PC with a software specially designed for recording and analysis of VLF data. Some examples of whistlers and VLF emissions recorded by the new set-up are presented and their frequency-time characteristics are discussed thoroughly. Page(s): 349-352

Low frequency dielectric dispersion and microwave permittivities of Indian granites

2005-10-01T00:00:00Z

Title: Low frequency dielectric dispersion and microwave permittivities of Indian granites Authors: Sengwa, R J; Soni, A Abstract: The complex dielectric permittivity ɛ*(ω) = ɛ'- jɛ" of 20 Indian granite samples from various localities in India were studied in the low frequency range 0.10-100 kHz and also at microwave frequency, i.e. 10.1 GHz at room temperature. All the studied dry samples showed the dielectric dispersion in the low frequency range. These are characterized by principal relaxation time with Cole-Cole dielectric dispersion model. The values of static dielectric constant ɛ_o, high frequency limiting dielectric constant ɛ_∞, distribution parameter α, and relaxation time τ of these samples were determined from their Cole-Cole plots. The frequency dependent ac conductivity of these granite samples were also determined and discussed. The real part of dielectric constant ɛ' of dry granite samples at 10.1 GHz was found to be in the range 4.5-8.3. Clear convincing correlation was observed between the microwave frequency ɛ' values with the samples bulk density. The plot of ɛ' values versus bulk density of the studied granite samples were represented by two straight lines of different slopes. The density reduced microwave permittivity values ɛ'_dr of granite samples were found to be in the range 1.81-1.99. For all the studied granite samples dielectric loss ɛ" was found to be less than 0.5 at microwave frequency. Microwave permittivities of porous samples with water saturation were also measured and these values were compared with the permittivity values computed from the dielectric mixing equation, complex refractive index model and the self-similar model using the microwave permittivities of dry samples and water. Page(s): 341-348