Showing papers in "Radio Science in 2017"

A Wideband Cross Polarization Conversion Using Metasurface

Abstract: A cross polarization conversion (CPC) structure using metasurface over wide bandwidth has been presented for practical applications in this article. The unit cell of the proposed metasurface is made of metallic patch of single circular split-ring imprinted on top surface of a metal-backed single layer dielectric substrate. Full width half maxima bandwidth of polarization conversion ratio (PCR) of 11.12 GHz is realized along with wide bandwidth of 9.92 GHz extending from 6.06 GHz to 15.98 GHz with more than 0.8 PCR magnitude is realized using suitable optimization of the geometrical dimensions. Four distinct PCR peaks are observed at 6.56 GHz, 10.38 GHz, 15.12 GHz and 16.68 GHz. The polarization conversion phenomena at these four frequencies have been analyzed in the light of electromagnetic resonances. The roles of several geometrical parameters of the design are simultaneously investigated. The proposed structure has been studied under oblique incidence, both for TE and TM polarizations. Wideband polarization conversion characteristics upto 45° incident angles have been observed for both cases. A prototype of the proposed metasurface is fabricated and experimental results are in good agreement with the simulated responses. The proposed structure is ultra-thin; ~ λ/11.8 with respect to the centre frequency of the CPC bandwidth.

Scattering by a zero‐thickness PEC disk: A new analytically regularizing procedure based on Helmholtz decomposition and Galerkin method

Abstract: The aim of this paper is the introduction of a new analytically regularizing procedure, based on Helmholtz decomposition and Galerkin method, successfully employed to analyze the electromagnetic scattering by zero-thickness perfectly electrically conducting circular disk. After expanding the fields in cylindrical harmonics, the problem is formulated as an electric field integral equation in the vector Hankel transform domain. Assuming as unknowns the surface curl-free and divergence-free contributions of the surface current density, a second-kind Fredholm infinite matrix-operator equation is obtained by means of Galerkin method with expansion functions reconstructing the expected physical behavior of the surface current density and with closed-form spectral domain counterparts, which form a complete set of orthogonal eigenfunctions of the most singular part of the integral operator. The coefficients of the scattering matrix are single improper integrals which can be quickly computed by means of analytical asymptotic acceleration technique. Comparisons with the literature have been provided in order to show the accuracy and efficiency of the presented technique.

Modeling and design for electromagnetic surface wave devices

Abstract: A great deal of interest has re-emerged recently in the study of surface waves. The possibility to control and manipulate electromagnetic wave propagations at will opens many new research areas and leads to lots of novel applications in engineering. In this paper, we will present a comprehensive modeling and design approach for surface wave cloaks, based on Graded-Refractive-Index materials and the theory of Transformation Optics. It can be also applied to any other forms of surface wave manipulation, in terms of amplitude and phase. In this paper, we will present a general method to illustrate how this can be achieved from modeling to the final design. The proposed approach is validated to be versatile and allows ease in manufacturing, thereby demonstrating great potential for practical applications.

Compact Single‐Layer Traveling‐Wave Antenna DesignUsing Metamaterial Transmission Lines

Abstract: This paper presents a single-layer traveling-wave antenna (TWA) that is based on composite right/left-handed (CRLH)-metamaterial (MTM) transmission line (TL) structure, which is implemented by using a combination of interdigital capacitors and dual-spiral inductive slots. By embedding dual-spiral inductive slots inside the CRLH MTM-TL results in a compact TWA. Dimensions of the proposed CRLH MTM-TL TWA is 21.5 x 30.0 mm(2) or 0.372 lambda(0) x 0.520 lambda(0) at 5.2 GHz (center frequency). The fabricated TWA operates over 1.8-8.6 GHz with a fractional bandwidth greater than 120%, and it exhibits a peak gain and radiation efficiency of 4.2 dBi and 81%, respectively, at 5 GHz. By avoiding the use of lumped components, via-holes or defected ground structures, the proposed TWA design is economic for mass production as well as easy to integrate with wireless communication systems.

Calculating the absorption of HF radio waves in the ionosphere

Abstract: It has long been known that the ionospheric absorption of HF radio waves is dependent on the electron density in the ionosphere. This paper examines two aspects of the absorption calculation that have not been as thoroughly investigated. First, the correct method to calculate ionospheric absorption is explored; while the Sen Wyller ray trace formulation is generally cited as the best approximation in the D and E regions of the ionosphere, the Appleton-Hartree formulation is more consistent with the theory in the F region of the ionosphere. It is shown that either ray trace formulation can be used to calculate ionospheric absorption if the correct collision frequencies are utilized. Another frequently overlooked aspect of the attenuation calculation are the variations in the electron-neutral and electron-ion collision frequencies as a function of local time, season, latitude, and solar cycle. These variations result in differences on the order of 30% in the total ionospheric attenuation and should be included in absorption calculations.

Electrostatic Potential Radiated by a Pulsating Charge in a Two‐Electron Temperature Plasma

Abstract: Mutual impedance experiments have been developed to constrain the plasma bulk properties, such as density and temperature, of ionospheric and later space plasmas, through the electric coupling between an emitter and a receiver electric antennas. So far, the analytical modeling of such instruments has enabled to treat ionospheric plasmas, where charged particles are usually well characterized by Maxwellian electron distributions. With the growth of planetary exploration, mutual impedance experiments are or will be used to constrain space plasma bulk properties. Space plasmas are usually out of local thermodynamic equilibrium; therefore, new methods to calibrate and analyze mutual impedance experiments are now required in such non-Maxwellian plasmas. To this purpose, this work aims at modeling the electric potential generated in a two-electron temperature plasma by a pulsating point charge. A numerical method is developed for the computation of the electrostatic potential in a sum of Maxwellian plasmas. After validating the method, the results are used to build synthetic mutual impedance spectra and quantify the effect of a warm electron population on mutual impedance experiments, in order to illustrate how the method could be applied for recent and future planetary space missions, such as Rosetta, BepiColombo, and JUICE. In particular, we show how it enables to separate the densities and temperatures of two different electron populations using in situ measurements from the RPC-MIP mutual impedance experiment on board Rosetta.

Polar mesospheric horizontal divergence and relative vorticity measurements using multiple specular meteor radars

Abstract: We present the first horizontal divergence and relative vorticity measurements at polar mesospheric altitudes measured from the ground. Our technique relies on combining information from two specular meteor radars (SMRs) separated 130 km at polar latitudes, specifically, the Andenes and Tromso radars in northern Norway. The resulting values are obtained over a region that spans an approximate area of 400 km diameter at mesospheric altitudes. The temporal and vertical resolution are 1 h and 2 km in altitude. The technique not only allows to obtain the gradient terms of the horizontal wind, that in turn are used to derive the horizontal divergence and relative vorticity, but also improves the horizontal sampling compared to single SMRs. Synthetic data are used to qualitatively test the technique and identify potential sources of biases on the resulting measurements. For example, we have found that an apparent large mean vertical velocity is obtained, after averaging many days, if there is a persistent divergent field. We present a climatology of the resulting wind field parameters from 12 years of continuous observations and focus on the summer results. We found a persistent altitudinal pattern in both the horizontal divergence and relative vorticity fields during all northern hemispheric summers. The horizontal divergence is mainly positive decreasing in magnitude below ∼86 km, and the relative vorticity is negative/positive below/above ∼88 km over northern Norway.

Elevation angle determination for SuperDARN HF radar layouts

Abstract: The international scientific radars known as the Super Dual Auroral Radar Network (SuperDARN) are designed to primarily measure plasma convection at ionospheric altitudes over a large region of the northern and southern hemispheres. SuperDARN radars are equipped with a secondary interferometry array that is used to measure the elevation angle (α) of signals. These values of α have been used in relatively few studies, however, they are important for estimating ionospheric quantities and for accurate geolocation of the ionospheric source region of backscattered signals. The majority of SuperDARN radars are constructed with interferometers that are separated from their main array in one or two dimensions and a relatively straightforward algorithm gives reasonably accurate results. A solution to the more general case, where offsets in all three dimensions are present, is desirable for future designs and necessary for at least one operational radar. Details of such an algorithm are described here and applied to phase measurements from several radars. For radars with interferometers offset only along the radar boresight and vertical directions, small differences of up to ∼1.5∘ in α are observed and negative values of α, which are deemed unphysical, are no longer produced. For the radar interferometer that is offset in all three dimensions the resulting values of α are consistent with expected behavior. The algorithm presented here provides a technique for accurately determining α from SuperDARN radars with offsets in all three dimensions and significantly reduces any constraints placed on the positioning of interferometers for future SuperDARN radars.

Artificial ionospheric modification: The Metal Oxide Space Cloud experiment

Abstract: Clouds of vaporized samarium (Sm) were released during sounding rocket flights from the Reagan Test Site, Kwajalein Atoll in May 2013 as part of the Metal Oxide Space Cloud (MOSC) experiment. A network of ground-based sensors observed the resulting clouds from five locations in the Republic of the Marshall Islands. Of primary interest was an examination of the extent to which a tailored radio frequency (RF) propagation environment could be generated through artificial ionospheric modification. The MOSC experiment consisted of launches near dusk on two separate evenings each releasing ~6 kg of Sm vapor at altitudes near 170 km and 180 km. Localized plasma clouds were generated through a combination of photoionization and chemi-ionization (Sm + O → SmO+ + e–) processes producing signatures visible in optical sensors, incoherent scatter radar, and in high-frequency (HF) diagnostics. Here we present an overview of the experiment payloads, document the flight characteristics, and describe the experimental measurements conducted throughout the 2 week launch window. Multi-instrument analysis including incoherent scatter observations, HF soundings, RF beacon measurements, and optical data provided the opportunity for a comprehensive characterization of the physical, spectral, and plasma density composition of the artificial plasma clouds as a function of space and time. A series of companion papers submitted along with this experimental overview provide more detail on the individual elements for interested readers.

Power allocation for target detection in radar networks based on low probability of intercept: A cooperative game theoretical strategy

Abstract: Distributed radar network systems have been shown to have many unique features. Due to their advantage of signal and spatial diversities, radar networks are attractive for target detection. In practice, the netted radars in radar networks are supposed to maximize their transmit power to achieve better detection performance, which may be in contradiction with low probability of intercept (LPI). Therefore, this paper investigates the problem of adaptive power allocation for radar networks in a cooperative game-theoretic framework such that the LPI performance can be improved. Taking into consideration both the transmit power constraints and the minimum signal to interference plus noise ratio (SINR) requirement of each radar, a cooperative Nash bargaining power allocation game (NBPAG) based on LPI is formulated, whose objective is to minimize the total transmit power by optimizing the power allocation in radar networks. First, a novel SINR-based network utility function is defined and utilized as a metric to evaluate power allocation. Then, with the well-designed network utility function, the existence and uniqueness of the Nash bargaining solution (NBS) are proved analytically. Finally, an iterative Nash bargaining algorithm is developed that converges quickly to a Pareto optimal equilibrium for the cooperative game. Numerical simulations and theoretic analysis are provided to evaluate the effectiveness of the proposed algorithm.

Study of wave-particle interactions for whistler-mode waves at oblique angles by utilizing the gyroaveraging method†

Abstract: We investigate the properties of whistler mode wave-particle interactions at oblique wave normal angles to the background magnetic field. We find that electromagnetic energy of waves at frequencies below half the electron cyclotron frequency can flow nearly parallel to the ambient magnetic field. We thereby confirm that the gyroaveraging method, which averages the cyclotron motion to the gyrocenter and reduces the simulation from two-dimensional to one-dimensional, is valid for oblique wave-particle interaction. Multiple resonances appear for oblique propagation but not for parallel propagation. We calculate the possible range of resonances with the first-order resonance condition as a function of electron kinetic energy and equatorial pitch angle. To reveal the physical process and the efficiency of electron acceleration by multiple resonances, we assume a simple uniform wave model with constant amplitude and frequency in space and time. We perform test particle simulations with electrons starting at specific equatorial pitch angles and kinetic energies. The simulation results show that multiple resonances contribute to acceleration and pitch angle scattering of energetic electrons. Especially, we find that electrons with energies of a few hundred keV can be accelerated efficiently to a few MeV through the n = 0 Landau resonance.

A physics-based model for the ionization of samarium by the MOSC chemical releases in the upper atmosphere

Abstract: Atomic samarium has been injected into the neutral atmosphere for production of electron clouds that modify the ionosphere. These electron clouds may be used as high-frequency radio wave reflectors or for control of the electrodynamics of the F region. A self-consistent model for the photochemical reactions of Samarium vapor cloud released into the upper atmosphere has been developed and compared with the Metal Oxide Space Cloud (MOSC) experimental observations. The release initially produces a dense plasma cloud that that is rapidly reduced by dissociative recombination and diffusive expansion. The spectral emissions from the release cover the ultraviolet to the near infrared band with contributions from solar fluorescence of the atomic, molecular, and ionized components of the artificial density cloud. Barium releases in sunlight are more efficient than Samarium releases in sunlight for production of dense ionization clouds. Samarium may be of interest for nighttime releases but the artificial electron cloud is limited by recombination with the samarium oxide ion.

A Neural Network based foF2 model for a single station in the polar cap

Abstract: A Neural Network (NN) model has been developed for the critical frequency of the F2 layer (foF2) at Resolute (7470∘ N, 26510∘ E) using data obtained from the Space Physics Interactive Data Resource, SPIDR (no longer available), for the period between 1975 - 1995 This model is a first step towards addressing the discrepancies of the International Reference Ionosphere (IRI) foF2 or peak electron density (NmF2) at high latitudes recently presented by Themens et al [2014] The performance of the NN model has been evaluated using foF2 data obtained from the Canadian Advanced Digital Ionosonde (CADI) at Resolute (7475∘ N, 26500∘ E) for the period between 2009 - 2013, in comparison with the IRI predictions The 2012 version, and the International Union of Radio Science (URSI) option of IRI has been used The NN nighttime monthly median foF2 variation demonstrates good agreement with observations compared to the IRI The NN model is able to reproduce the enhancements in foF2 during the equinoxes, and also shows an improvement during disturbed days Root Mean Square Errors (RMSE) were computed between hourly and monthly median model predictions and observations, and on the whole, the NN model seems to perform better during low solar activity and the equinoxes The NN model shows an improvement in performance on average by 26638% for hourly foF2 and 32636% for monthly median foF2, compared to 7877% obtained for the same station by the most recent NN model that attempted to predict foF2 at a polar cap station [Oyeyemi 24 and Poole, 2005]

The Accuracy of Radio Direction Finding in the Extremely Low Frequency Range

Abstract: In this work, we study the accuracy of direction finding in the Extremely Low Frequency (ELF) range using a newly installed broadband receiver equipped with two active magnetic antennas. The main natural source of ELF radio waves is lightning. In this work, we analyzed 1000 atmospheric discharges at distances of up to 5000 km from the receiver. We identified the most important factors influencing the accuracy of the angle of arrival: the deviation of the radio waves propagating through the day-night terminator zone and the signal-to-noise ratio resulting from local electromagnetic noise and Schumann Resonance background. The obtained results clearly show that the accuracy of estimating the direction of arrival is very high (an average error of 0.1° with the standard deviation of 2.3°) when the signal-to-noise ratio is large (the amplitude of the magnetic field component above 100 pT), except for short periods in the local morning and evening, when the day-night terminator is present on the propagation path of the direct wave. For the day-night propagation paths, the refraction angle was larger than the incidence angle, and for the night-day propagation paths, the refraction angle was smaller than the incidence angle, which is consistent with theory. Using our analytical ELF radio propagation model allowed us to explain the obtained results.

Direct MSTID mitigation in precise GPS processing

Abstract: In this paper, the authors summarize a simple and efficient approach developed to mitigate the problem in precise Global Navigation Satellite Systems (GNSS) positioning originated by the most frequent ionospheric wave signatures: the medium-scale traveling ionospheric disturbances (MSTIDs). The direct GNSS Ionospheric Interferometry technique (hereinafter dGII), presented in this paper, is applied for correcting MSTID effects on precise Real Time Kinematic (RTK) and tropospheric determination. It consists of the evolution of the former climatic Differential Delay Mitigation Model for MSTIDs (DMTID), for real-time conditions, using ionospheric data from a single permanent receiver only. The performance is demonstrated with networks of GNSS receivers in Poland, treated as users under real-time conditions, during two representative days in winter and summer seasons (days 353 and 168 of year 2013). In range domain, dGII typically reduces the ionospheric delay error up to 10–90% of the value when the MSTID mitigation model is not applied. The main dGII impact on precise positioning is that we can obtain reliable RTK position faster. In particular, the ambiguity success rate parameter increases, from 74% to 83%, with respect to the original uncorrected observations. The average of time to first fix is shortened from 30 s to 13 s. The improvement in troposphere estimaton, due to any potential impact of the MSTID mitigation model, was most difficult to demonstrate.

Multiinstrument observations of a geomagnetic storm and its effects on the Arctic ionosphere: A case study of the 19 February 2014 storm

Abstract: We present a multiinstrumented approach for the analysis of the Arctic ionosphere during the 19 February 2014 highly complex, multiphase geomagnetic storm, which had the largest impact on the disturbance storm-time index that year. The geomagnetic storm was the result of two powerful Earth-directed coronal mass ejections (CMEs). It produced a strong long lasting negative storm phase over Greenland with a dominant energy input in the polar cap. We employed global navigation satellite system (GNSS) networks, geomagnetic observatories, and a specific ionosonde station in Greenland. We complemented the approach with spaceborne measurements in order to map the state and variability of the Arctic ionosphere. In situ observations from the Canadian CASSIOPE (CAScade, Smallsat and Ionospheric Polar Explorer) satellite's ion mass spectrometer were used to derive ion flow data from the polar cap topside ionosphere during the event. Our research specifically found that (1) thermospheric O/N 2 measurements demonstrated significantly lower values over the Greenland sector than prior to the storm time. (2) An increased ion flow in the topside ionosphere was observed during the negative storm phase. (3) Negative storm phase was a direct consequence of energy input into the polar cap. (4) Polar patch formation was significantly decreased during the negative storm phase. This paper addresses the physical processes that can be responsible for this ionospheric storm development in the northern high latitudes. We conclude that ionospheric heating due to the CME's energy input caused changes in the polar atmosphere resulting in N e upwelling, which was the major factor in high-latitude ionosphere dynamics for this storm.

Assessment of GPS Multifrequency Signal Characteristics During Periods of Ionospheric Scintillations from an Anomaly Crest Location

Abstract: Multi-frequency GPS transmissions have provided the opportunity for testing the applicability of the principle of frequency diversity for scintillation mitigation. Published results addressing this issue with quantified estimates are not available in literature, at least from the anomaly crest location of the Indian longitude sector. Multi-frequency scattering within the same L-band are often the attributed cause behind simultaneous decorrelated signal fluctuations. The present paper aims to provide proportion of time during scintillation patches that decorrelations are found across GPS L1, L2 and L5 frequencies associated with high S4, corresponding high values of scattering coefficients and large receiver position deviations thereby seriously compromising the performance of satellite based navigation system. Results from the anomaly crest station at Calcutta indicate maximum 40% of scintillation time during February-April 2014 and 33% during August-October 2014 that the signals are decorrelated. It is important to note that it is only during these time intervals that the principle of frequency diversity could be applied for scintillation mitigation.

The Electromagnetic Field for a PEC Wedge Over a Grounded Dielectric Slab: 1. Formulation and Validation

Abstract: Complex scattering problems are often made by composite structures where wedges and penetrable substrates may interact at near field. In this paper (Part I) together with its companion paper (Part II) we study the canonical problem constituted of a Perfectly Electrically Conducting (PEC) wedge lying on a grounded dielectric slab with a comprehensive mathematical model based on the application of the Generalized Wiener-Hopf Technique (GWHT) with the help of equivalent circuital representations for linear homogenous regions (angular and layered region). The proposed procedure is valid for the general case and the papers focus on E-polarization. The solution is obtained using analytical and semi-analytical approaches that reduce the Wiener-Hopf factorization to integral equations. Several numerical test cases validate the proposed method. The scope of Part I is to present the method and its validation applied to the problem. The companion paper Part II focuses on the properties of the solution and it presents physical and engineering insights as GTD/UTD diffraction coefficients, total far fields, modal fields and excitation of surface and leaky waves for different kinds of source. The structure is of interest in antenna technologies and electromagnetic compatibility (tip on a substrate with guiding and antenna properties).

Artificial magnetic conductor-based circularly polarized crossed-dipole antennas: 1. AMC structure with grounding pins

Abstract: In this paper, we analyze low-profile circularly polarized (CP) antennas comprising a crossed-dipole radiator on finite artificial magnetic conductor (AMC) surfaces. The crossed dipole is fed by a pair of vacant-quarter printed rings to produce CP radiation. The AMC structure consists of a lattice of square metal plates on a grounded dielectric substrate with connecting pins between the patches and the ground plane. In this paper, we focus on the excitation of surface waves propagating on the finite-sized AMC surface, which generates extra resonances and CP radiations for the radiation structures. We predict the surface-wave resonances using a cavity model. In this model, the finite-sized AMC structure is considered as a waveguide resonator. We verify the predicted results computationally using the finite element method-based full-wave electromagnetic solver Ansoft high-frequency structure simulator. The results show that these extra resonances and corresponding CP radiations can be used to broaden the impedance matching and axial ratio bandwidths of the antennas, respectively.

State of the Art and Challenges of Radio Spectrum Monitoring in China

Abstract: This paper provides an overview of radio spectrum monitoring in China. First, research background, the motivation is described and then train of thought, the prototype system, and the accomplishments are presented. Current radio spectrum monitoring systems are man-machine communication systems, which are unable to detect and process the radio interference automatically. In order to realize intelligent radio monitoring and spectrum management, we proposed an Internet of Things-based spectrum sensing approach using information system architecture and implemented a pilot program; then some very interesting results were obtained.

A Study of Daytime L-Band Scintillation in Association With Sporadic E Along the Magnetic Dip Equator

Abstract: American Geophysical Union. All Rights Reserved. In this paper, we present a comprehensive study of occurrence of L-band scintillation in association with the appearance of sporadic E (Es) along the magnetic dip equator during daytime in 2013. The presence of L-band scintillation was determined from signals collected with GNSS (Global Navigation Satellite Systems) ground-based Scintillation Network Decision Aid receivers from five stations situated at the magnetic dip equator. The detection and analysis of Es layers were obtained from GNSS FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (F3/C) radio occultation (RO) data. Combining ground-based data with the limb-viewing geometry from space provides a unique opportunity to retrieve complementary information about scintillation and association with equatorial E region irregularities (i.e., Es) during daytime. Results for the first time show that daytime scintillation does occur at the magnetic dip equator and the occurrence is associated with the appearance of Es observed using GNSS F3/C RO data.

Evaluation of extreme ionospheric total electron content gradient associated with plasma bubbles for GNSS Ground-Based Augmentation System

Abstract: Associated with plasma bubbles, extreme spatial gradients in ionospheric total electron content (TEC) were observed on 8 April 2008 at Ishigaki (24.3°N, 124.2°E, +19.6° magnetic latitude), Japan. The largest gradient was 3.38 TECU km −1 (total electron content unit, 1 TECU = 10 16 el m −2 ), which is equivalent to an ionospheric delay gradient of 540 mm km −1 at the GPS L1 frequency (1.57542 GHz). This value is confirmed by using multiple estimating methods. The observed value exceeds the maximum ionospheric gradient that has ever been observed (412 mm km −1 or 2.59 TECU km −1 ) to be associated with a severe magnetic storm. It also exceeds the assumed maximum value (500 mm km −1 or 3.08 TECU km −1 ) which was used to validate the draft international standard for Global Navigation Satellite System (GNSS) Ground-Based Augmentation Systems (GBAS) to support Category II/III approaches and landings. The steepest part of this extreme gradient had a scale size of 5.3 km, and the front-normal velocities were estimated to be 71 m s −1 with a wavefront-normal direction of east-northeastward. The total width of the transition region from outside to inside the plasma bubble was estimated to be 35.3 km. The gradient of relatively small spatial scale size may fall between an aircraft and a GBAS ground subsystem and may be undetectable by both aircraft and ground.

Separation of O/X Polarization Modes on Oblique Ionospheric Soundings

Abstract: The oblique-incidence sounder (OIS) is a well-established instrument for determining the state of the ionosphere, with several advantages over vertical-incidence sounders (VIS). However, the processing and interpretation of OIS ionograms is more complicated than that of VIS ionograms. Due to the Earth's magnetic field, the ionosphere is birefringent at radio frequencies and a VIS or OIS will typically see two distinct ionospheric returns, known as the O- and X-modes. The separation of these two modes on a VIS, using a polarimetric receive antenna, is a well-established technique. However, this process is more complicated on an OIS due to a variable phase separation in the phase difference between the two modes, as measured between the two arms of a polarimetric antenna. Using a polarimetric antenna that can be rotated and tilted, we show that this variation in phase separation within an ionogram is caused by the variation in incidence angle, with some configurations leading to greater variation in phase separation. We then develop an algorithm for separating O- and X-modes in oblique ionograms which can account for the variation in phase separation and we demonstrate successful separation even in relatively difficult cases. The variation in phase separation can also be exploited to estimate the incident elevation, a technique which may be useful for other applications of HF radio.

State-space models and stored electromagnetic energy for antennas in dispersive and heterogeneous media

Abstract: Accurate and efficient evaluation of the stored energy is essential for Q factors, physical bounds, and antenna current optimization. Here it is shown that the stored energy can be estimated from quadratic forms based on a state-space representation derived from the electric and magnetic field integral equations. The derived expressions are valid for small antennas embedded in temporally dispersive and inhomogeneous media. The quadratic forms also provide simple single frequency formulas for the corresponding Q factors. Numerical examples comparing the different Q factors are presented for dipole and meander line antennas in conductive, Debye, and Lorentz media for homogeneous and inhomogeneous media. The computed Q factors are also verified with the Q factor obtained from the stored energy in Brune synthesized circuit models. (Less)

Interferometer angle-of-arrival determination using precalculated phases

Abstract: A method has been developed to determine the angle-of-arrival (AoA) of incident radiation using pre-computed lookup tables. The phase difference between two receiving antennas can be used to infer AoA as measured from the pair baseline, but there will be more than one possible solution for antenna spacings greater than or equal to half a wavelength. Larger spacings are preferable to minimize mutual coupling of elements in the receive array and to decrease the relative uncertainty in measured phase difference. We present a solution that uses all unique antenna pairs to determine probabilities for all possible azimuth and zenith values. Prior to analysis, the expected phase differences for all AOAs are calculated for each antenna pair. For a received signal, histograms of possible AoAs for each antenna pair phase difference are extracted and added to produce a two dimensional probability density array that will maximize at the true value of the AoA. A benefit of this method is that all possible antenna pairs are utilized, rather than the restriction to specific pairs along baselines used by some interferometer algorithms. Numerical simulations indicate that performance of the suggested algorithm exceeds that of existing methods, with the benefit of additional flexibility in antenna placement. Meteor radar data has been used to test this method against existing methods, with excellent agreement between the two approaches. This method of AoA determination will allow the construction of low-cost interferometric direction finding arrays with different layouts, including construction of difficult terrain and three-dimensional antenna arrangements.

Sura heating facility transmissions to the CASSIOPE/e‐POP satellite

Abstract: Throughout a night-time pass of the CASSIOPE satellite at an altitude of about 1300 km above the Sura Heating Facility, transmission of O-mode radiation from Sura to the ePOP Radio Receiver Instrument on CASSIOPE was maintained. Also during this pass, continuous VHF/UHF transmission from the ePOP CERTO radio beacon to three coordinated ground receivers in the Sura vicinity was achieved. Tomography of the VHF/UHF received wave data based on total electron content permitted the two-dimensional distribution of ionospheric ambient electron plasma frequency fpe to be determined in the latitude-altitude space between Sura and CASSIOPE. foF2 values about 0.1 MHz above the Sura pump frequency of 4.3 MHz were measured by the tomography. We examine the question of whether the observations can be explained on the basis of classic propagation in a smooth ionosphere. Tracing of rays from Sura towards CASSIOPE orbital locations finds most rays reflected away from the topside by the patchy ionospheric structure in bottomside fpe. It is concluded that O-mode ducting in under-dense field-aligned irregularities is responsible for maintaining the transionospheric transmission across the 2-min pass. O-to-Z mode “radio-window” conversion in the F-region bottomside is not required to explain these data.

Impact of multiconstellation satellite signal reception on performance of satellite‐based navigation under adverse ionospheric conditions

Abstract: Application of multi-constellation satellites to address the issue of satellite signal outages during periods of equatorial ionospheric scintillations could prove to be an effective tool for maintaining the performance of satellite-based communication and navigation without compromise in accuracy and integrity. A receiver capable of tracking GPS, GLONASS and GALILEO satellites is operational at the Institute of Radio Physics and Electronics, University of Calcutta, Calcutta, India located near the northern crest of the Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The present paper shows increased availability of satellites combining GPS, GLONASS and GALILEO constellations from Calcutta compared to GPS-only scenario and estimates intense scintillation-free (S4 < 0.6) satellite vehicle look angles at different hours of the post-sunset period 19:00-01:00LT during March 2014. A representative case of March 1, 2014 is highlighted in the paper and overall statistics for March 2014 presented to indicate quantitative advantages in terms of scintillation-free satellite vehicle look angles that may be utilized for planning communication and navigation channel spatial distribution under adverse ionospheric conditions. Number of satellites tracked and receiver position deviations has been found to show a good correspondence with the occurrence of intense scintillations and poor user receiver-satellite link geometry. The ground projection of the 350-km subionospheric points corresponding to multi-constellation shows extended spatial coverage during periods of scintillations (0.2 < S4 < 0.6) compared to GPS.