In Search and Rescue (SaR) operations, a Ground Penetrating Radar (GPR) constitutes a good way to detect buried people under debris. Coupled to an autonomous system, we obtain a very efficient tool available to access otherwise hard-to-reach spatial domains for the rescuers. Such areas are characterised by very hostile conditions. Such zones are treacherous due to their inherent instability and due to the restricted mobility in such environments: holes and deep subsidence, geological crevices, narrow passages, etc.
Indian Regional Navigation Satellite System operates on L-band and S-band frequencies [1]. The S-band spectrum is congested with several other signals including the signals operating in the license free band. IRNSS S-band signals are therefore more vulnerable to Radio Frequency Interference (RFI) from various terrestrial S-band sources like Wi-Fi and Bluetooth [2]. This paper investigates IRNSS S-band signal performance in the presence of terrestrial Bluetooth signals.
Over the years, microwave subsurface imaging has gained widespread attention in many fields such as concealed weapon detection at security checkpoints, landmine detection, biomedical imaging, structural health monitoring, quality inspection of composite structures etc. The strategy of microwave imaging is to illuminate the object under investigation using a known electromagnetic source, and from the reflection and transmission parameters received in response, information regarding the electromagnetic signature of the target is derived using suitable inverse process. Of the various measurement techniques available, the criteria for selecting a particular scheme for microwave imaging would be primarily based on factors such as the ease of imaging, frequency of operation, imaging accuracy etc. In recent years, real-time imaging of objects has garnered interest where the imaging scheme does not involve complex iterative inverse solutions or time-consuming calibration procedures [1]. Accordingly, the focus has been shifted from theoretical studies to the development of sophisticated practical arrangements where one can acquire information about objects in real time.
Scalar potential finite difference (SPFD) [1] method has been commonly used to estimate internal electric fields in the human body exposed to electric fields in the frequency range where quasi-static approximation can be applied. The simultaneous linear equations of the SPFD calculation is consistent only when the sum of the right hand side vector elements is zero. Here, the right hand side vector corresponds to the current distribution on the surface of biological object. However, the sum of the right hand side vector elements hardly become zero when the actual exposure scenario is assumed, because the boundary condition of current distribution on the surface of biological object is derived from another numerical scheme which essentially contains numerical errors. Some iterative methods can not be applied to this inconsistent linear equations because a significant error or divergence occurs. Therefore, the purpose of this study is to avoid inconvenience in solving such a large scale simultaneous linear equations, and to investigate the high efficiency technique for SPFD method.
This paper proposed the Tri band antenna using L shape parasitic. The rectangular patch antenna works as driven element. FR4 is used as dielectric material. First the simple RMSA is design for frequency 2.4 GHz and after the effect of parasitic is considered. This proposed antenna covers the L, S, C bands with enhanced impedance bandwidth in each band.
Excitation of electromagnetic waves by distributed given sources located on the surface of an open cylindrical waveguide filled with a gyrotropic medium is studied. It is assumed that the waveguide is placed in free space and aligned with an external static magnetic field. The considered sources have nonsymmetric electric-current distributions. The radiation resistances of the sources are numerically calculated using an approach based on an expansion of the total field in terms of the discrete-and continuous-spectrum waves.
Attacks by Jamming on wireless communication network can provoke Denial of Services. According to the communication system which is affected, the consequences can be more or less critical. In this paper, we propose to develop an algorithm which could be implemented at the reception stage of a communication terminal in order to detect the presence of jamming signals. The work is performed on Wi-Fi communication signals and demonstrates the necessity to have a specific signal processing at the reception stage to be able to detect the presence of jamming signals.
Evolution of the ozone layer is significantly influenced by the changes in the climate. By ozone layer one means the lower region of the stratosphere, where the ozone concentration is relatively higher than the other layers. Changes in the transport process, chemical composition and temperature in this layer very often results from the variations in the climate [1]. Enhancement in the greenhouse effect has led to an increase in the tropospheric ozone concentration since 1900. A time series is a particular realization of a stochastic process. A stochastic model is a structured expression of a stochastic process. Markov chain and autoregressive models are examples of stochastic models, and these have been of vital importance in studying meteorological processes, and a handful of works of literature are available where time series for variables associated with meteorological processes have been investigated through stochastic models [2]. This study reports univariate modeling methodologies applied to the monthly total ozone concentration (TOC) over Kolkata, India, derived from the measurements made by the Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS). In the present work, the data collected from measurements made by EP/TOMS.
Traditionally, radar rainfall algorithms are derived through nonlinear regression of rain rates and simulated radar observables from raindrop size distribution (DSD). The performance of such empirical relations is highly dependent on the physical model of DSD and the parametric relation between the physical model and radar parameters. Such algorithms also have large uncertainties that need to be adaptively adjusted based on local DSD properties. In this research, we propose an alternative approach to dual-polarization radar rainfall estimation. In particular, a non-parametric machine learning model is designed and trained using simulated radar data based on DSD measurements in different climatological regimes. The trained model is applied to real radar measurements to produce rain rate estimates. Preliminary results show the promising performance of this novel method compared to traditional parametric rainfall relations.
The radio-thermal emission from Venus as observed by ground-based interferometric radio-telescopes shows a significant spectral variation, with a gradual increase in brightness temperature from 1 mm to 6 cm and a decrease thereafter at higher wavelengths. The first time GMRT observations beyond 70 cm wavelength also reconfirm this decreasing trend in T-b with the increase in wavelength [7]. Efforts have been made to model this spectral variation in T-b [1], [10], but these models fail to explain the low-frequency radio-thermal emission from Venus (decrease in T-b with the increase in wavelength) and the problem still remains unresolved. The authors attempt to explain this problem using radiative transfer based model and radiometric observations of Venus focussing particularly on the higher wavelength T-b observations from the Giant meter radio telescope (GMRT). The GMRT brightness temperature (T-b) (at 0.21, 0.5, 0.9, 1.23 and 2 m) is observed to decrease with frequency. A radiative transfer model was developed and it is seen that a two layer Venusian surface model matches with the observations. Based on the simulation studies, the authors put forth a hypothesis that Venus may have an absorbing layer within the first few meter depth.
Maintenance of infrastructures, e.g. road, tunnel, bridge, etc., is one of most important issues that must be solved for sustainable society. It is usually measured and checked by human, however, it is very hard to measure a lot of infrastructures. Recently, new sensors to measure the infrastructures are developed and it is easy and convenient for the maintenance of the infrastructures. It is requested to expand a life time of the sensors. So battery-less sensor is hopeful expected because life time is decided by battery time.
The Upgraded GMRT provides near seamless frequency coverage from ~125 MHz to 1500 MHz with instantaneous bandwidths of up to 400 MHz using state of art technologies used for the front end electronics, signal processing systems, and monitor and control systems. The fiber optic signal transport system is an important part of a radio observatory. The GMRT observatory uses analogue fiber optic link to transports the radio astronomical signal from antenna base to the central electronics building for further signal processing. This report presents a digital fiber optic link for remote antenna application using wavelength-division-multiplexing (WDM) technique over a single fiber to co-exist with existing upgraded GMRT signal transport system and the legacy system of the GMRT. The network architecture is designed with low complexity, low cost and commercially available Ethernet transceiver modules. At each antenna base two polarizations are digitized and transported over 10GbE fiber optic link to the central electronics building. Additional wavelength is used to support the clock synchronization scheme of GMRT. Over the same single fiber a third wavelength is used for the remote antenna control and monitoring application. The overall signal transport system on single fiber supports 8 X 10GbE link to any remote antenna in the array.
Recent research on holographic and diffractive metasurfaces shows enormous promise for developing cheaper and more compact systems. A metasurface aperture exploits the phase shift inherent in the guided reference wave and avoids using active elements such as phase-shifters associated with conventional phased arrays and electronically scanned antennas. The radiation pattern can thus be controlled by altering properties of each metasurface element coupled to the reference wave. In this paper, we discuss parameters to control the metasurface for a radar or communications payload. In both cases, the reconstruction of the received aperture field relies on using computational imaging techniques on arbitrary and spatially diverse field patterns.
Solar flares are sudden and massive releases of magnetic energy in the corona. As a consequence, particles are efficiently accelerated to high energies and plasma is heated up to tens of millions K [1]. However, this phenomenon is dynamically and morphologically complex. A characteristic of this complexity is the creation of multiple acceleration sites due to the magnetic field reconfiguration. During the flare, the energetic electrons propagating in the loops emits in high-frequency radio wavelengths via gyrosyntrochton emission mechanism [2]. Some class of energetic particles may undergo plasma instabilities producing intense coherent radio emission [3]. Accelerated electrons and hot plasma also produce X-ray bremsstrahlung. The heated plasma filling the magnetic loops show up as bright emissions in various extreme ultra-violet (EUV) wavelengths. This entire flare process shows complex evolution at fine spatial, spectral and temporal scales. Therefore, a more comprehensive understanding of solar flares requires multi-wavelength analysis with observations that provide high spatial resolution coupled with high frequency and time resolution.
The Atmospheric Boundary Layer (ABL) height is measured with the help of Monostatic SODAR (Sonic Detection And Ranging) System [1]. Meteorological aspects of Doppler free acoustic sounding (Mono-static SODAR system) of the atmosphere are considered [2, 3]. This instrument plays an important role in ABL studies using remote sensing techniques, where other techniques (like Radio-sonde, LIDAR, and Mast etc.) are difficult and expensive. Various features of Mono-static SODAR records with direct measurements with meteorological sensors in ABL are analysed. Some primary results regarding the statistical analysis of the ABL height, meteorological parameters, atmospheric pollutants of main physical parameter of the ABL (Atmosphere) were shown and discussed for the metropolitan city Delhi during the periods of October 2016 to February 2017. During mid-October to mid-November low height of ABL were observed due to high concentration of atmospheric pollutants and low wind speed. During the period of mid-December 2016 to mid-January 2017, fog episodes and strong low level elevated and inversions were observed most of the time.
Megha-Tropiques (MT) satellite was launched with the aim to study convective systems, water cycle and energy budget and to improve the understanding on tropical weather events and the climate. SAPHIR is a millimeter wave payload aboard MT with six channels on the water vapor absorption band centered around 183.31 GHz. In contrast to earlier microwave humidity sounders SAPHIR has three additional channels and has improved vertical and horizontal resolutions. The low inclination orbit of MT ensures unprecedented coverage over global tropical region with revisits at different local times, which help to capture the weather related atmospheric variability.
Using an in-house developed one dimensional photo-chemical model (1D-PCM), which considers production and loss of 11 ions namely, CO 2 + , CO + , C + , N 2 + , N + , He + , O + ( 2 D), O + ( 2 P), O + ( 4 S), O 2 + and NO + , characteristics of the V2 layer in the Venus ionosphere has been studied. It is noted that existing ionospheric model for the Venus ionosphere, such as the IonA (Ionization in Atmospheres) model, not only over/under estimate the peak electron density of V2 layer, it also has significant departures from the observations on the solar zenith angle and solar activity control. The IonA model uses VenusGRAM model (Venus Global Reference Atmosphere Model) as input for the neutral density and considers Venus atmosphere consisting of CO 2 , O, and N 2 molecules only. Further, it oversimplifies the ion chemistry by assuming Venus ionosphere to have O 2 + as the only dominant ion species. Using VTS3 model, an empirical model based on measurements from Orbiter Neutral Mass Spectrometer on Pioneer Venus Orbiter (PVO) which considers profiles of six neutrals (CO 2 , O, CO, He, N, and N 2 ), we modified IonA model, named as IonA-VTS3, to find that it reproduced the altitude of V2 peak electron density (hmV 2 ) quite well. However, the model still lacked in reproducing observed peak V2 electron density (NmV 2 ). The in-house developed one dimensional photo-chemical model (1D-PCM) not only estimated NmV 2 accurately, the hmV 2 was also reproduced quite well. Comparison of Venera and PVO radio occultation measurements with 1D-PCM and IonA-VTS3 calculations reveals the role of complex chemical reactions in determining the features of peak altitude and density of V2 layer during different solar activity periods. We surmised that differences in the observed and IonA modeled peak V2 layer altitudes were due to the limitations associated with VenusGRAM neutral density model. It shows that variations in the neutral density controls the V2 layer peak density height. 1D-PCM calculations also showed that the complex chemistry including production and loss reactions of 11 ions could reproduce the variations in the peak density of Venusian ionosphere during different solar activity conditions. It suggests that the ion-chemistry has wider control over the peak plasma density in the Venus ionosphere.
A novel configuration of filtering antenna for C-band applications is presented in this paper. An elliptical radiator based UWB monopole antenna is first investigated and then integrated to a wideband bandpass filter to achieve high frequency selectivity as well as compactness. The bandpass filter is constituted by stepped impedance stub loaded resonator for C-band applications. Aperture backed inter-digital coupled lines are used to feed the multiple-mode resonator of proposed bandpass filter. The proposed filtenna leaves out the necessity of cascading any additional 50 Ω microstrip elements in between the developed antenna and filter, thus making the system smaller. The incorporation of planar antenna and the filter is carried out using FR4 substrate board with permittivity 4.4 and thickness 1.6 mm. The overall dimension of the wideband filtenna is obtained as 59×42 mm 2 . Performance analysis of the UWB antenna, bandpass filter and their integrated structure has been carried out systematically in this paper. An in-depth agreement between simulated and measured results is discovered for the proposed configurations.
In the low latitude ionosphere, the formation of Equatorial Plasma Bubbles presents a regular behavior under quiet conditions of the geospace. The ionospheric irregularities embedded in the plasma bubbles may lead to amplitude scintillation of Global Navigation Satellite Systems signals. Solar events disturb the regular behavior of the magnetosphere-ionosphere system, leading to an intensification or a suppression of such ionospheric irregularities producing scintillations. During the same storm, inhibition and intensification of the ionospheric scintillations can both occur, depending on the local time of the storm arrival and on the storm features. Electric fields penetrating from the auroral latitudes and disturbing the ionospheric electrodynamics are commonly highlighted as the principal responsible for the inhibited/enhanced scintillations. Beside this mechanism, the disturbance dynamo is the concurrent key-physical phenomenon, being due to variations of the thermospheric winds induced by heating convecting from high towards equatorial latitudes and disturbing the electrodynamics of the Equatorial Electrojet [1]. In the present work, we analyze the scintillation over San Miguel de Tucumán (Argentina), located under the southern crest of the Equatorial Ionospheric Anomaly, focusing on the multi-scale variability and on the causal relationship between forcing factors from the geospace and the ionospheric response.
Evolution, design concept and practical realization of multifunctional antennas (MFA) are systematically reported in this paper. MFAs, traditionally evolved as an intelligent solution to mitigate lower spectrum-utilization using the opportunistic spectrum allocation-policy, are key component for modern wireless applications, such as multi-standard radios, cognitive radios (CR) of software defined radio (SDR) environment. Traditional realizations of MFAs use multiple radiating elements on a common substrate which enhances design constrains in terms of mitigating/reducing parasitic coupling and spurious impacts of the rotary arrangements required for actuating various radiating elements. In this paper, recent research contribution of designing MFAs employing a single UWB radiating element is reported. Improvised feed design with combinatorial loading of SRRs and PIN diodes on a printed monopole antenna, along with controlling their position in the feed region, results into multifunctional operation. Design strategy, techniques, and theoretical ideas for realizing MFAs along with simulated and experimental results are presented in this paper.
