NOPR Collection:

Dual-frequency slot-loaded rectangular microstrip antenna

2014-01-15T16:41:58Z

Title: Dual-frequency slot-loaded rectangular microstrip antenna Authors: Kiran K, Usha; Vani, R M; Hunagund, P V Abstract: In this study, dual-frequency slot-loaded rectangular microstrip antennas were designed, fabricated and evaluated. The design consists of rectangular patch microstrip antenna loaded with a pair of narrow slots parallel and close to the radiating edges on the patch, which is feel by centre-fed microstripline feed.Spacing of the slots was taken equally from both edges of the corners.The characteristics like VSWR, return loss, input impedance, bandwidth, radiation pattern, HPBW, frequency ratio and gain were measured and analyzed for different spacings. Dual frequency operation has been achieved having low frequency ratio. Page(s): 75-78

Characterization of ferrite and silicon carbide based microwave absorber using FSS structures at X-band

2016-07-20T05:15:23Z

Title: Characterization of ferrite and silicon carbide based microwave absorber using FSS structures at X-band Authors: Meshram, M R; Agrawal, Nawal K; Sinha, Bharoti; Misra, P S Abstract: In this paper the experimental result of microwave absorber with a single layer coating of ferrite and silicon carbide (SiC) based paint for X-band is presented. Samples of M-type hexagonal ferrite powder [Ba(MnTi)₁₈Fe_8.4O₁₉] has been developed by dry attrition and sintering process. These developed ferrite powder and SiC powder have been mixed in epoxy resins to form a microwave absorbing paint. This paint was coated on aluminum sheet for absorption studies. The frequency selective surface (FSS) patterns are embedded on the surface of absorber sheet and tested experimentally at X-Band. It was found that SiC based microwave absorbing paint provide wide band absorption characteristics with minimum absorption of 10 dB from 9.5 to 12 GHz for a coating thickness of 1.84 mm. Page(s): 71-74

Estimation of emissivity and scattering coefficient of the constituents of vegetation at microwave frequencies

2016-07-20T05:14:34Z

Title: Estimation of emissivity and scattering coefficient of the constituents of vegetation at microwave frequencies Authors: Calla, O P N; Rai, Avdhesh Roop; Mathur, Prannoy; Mathur, Deepak; Bohra, Dinesh Abstract: A vegetation canopy is a dielectric mixture consisting of discrete dielectric inclusions (leaves, stalks and fruits) distributed in a host material (air). The scattering and emission behaviour of vegetation canopy made up of neem-like trees has been studied. The estimation of emissivity, brightness temperature and scattering coefficient has been made using the measured values of dielectric constant. The measurement of dielectric constant of neem leaves has been carried out using waveguide cell method in the frequency range of X-band (8.2 GHz-12.4 GHz) at 9.035 GHz. The estimations of emissivity, brightness temperature and scattering coefficient are made for incidence angles varying from 0° to 80° for both horizontal and vertical polarization. The results of emissivity and scattering coefficient so obtained have been presented. Page(s): 67-70

Study of infrasonic waves at low latitude northern hemisphere, India

2014-01-16T16:41:02Z

Title: Study of infrasonic waves at low latitude northern hemisphere, India Authors: Lal, M Abstract: The infrasonic waves have been studied at the low latitude station Tirunelveli (8.7°N,77.8°E), India, in northern hemisphere. Almost 50 events of the severe earthquake (Ms > 6.0) have been studied. The changes in surface pressure as well as acoustic waves produced have been recorded immediately after the earthquake. The Rayleigh waves-induced changes in surface pressure which cause significant changes in pressure have been recorded by all the systems. The arrival of acoustic waves followed by large decrease in pressure has also been recorded in almost all the cases. Only a few cases have been reported. The infrasonic waves between 10 and 100 s have been observed. The infrasonic waves produced from the unknown sources have also been observed. But their variation feature is different from the earthquake-induced infrasonic waves. The corresponding microbaroms obtained at this station show variation similar to the infrasonic waves. Page(s): 62-66