This paper presents the evaluation of the recently developed covariance model for the Ionospheric Data Assimilation Four-Dimensional (IDA4D) technique. The ionospheric data are generated using the Observation System Simulation Experiment Tool (OSSET) from the known ionospheric state produced by the physics-based Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIMEGCM)

Our knowledge of the internal structure of asteroids is currently indirect and relies on inferences from remote sensing observations of surfaces. However, it is fundamental for understanding small bodies’ history and for planetary defense missions. Radar observation of asteroids is the most mature technique available to characterize their inner structure, and Synthetic Aperture Radar Tomography (TomoSAR)

Ionospheric irregularities as plasma bubbles occur in the ionosphere, and generally, they are characterized by the low plasma density regions. The Rate Of TEC Index (ROTI) was defined in terms of the Total Electron Content (TEC) variation and is used to characterize these plasma bubbles. It is essential to evaluate the ROTI behavior since the ionospheric irregularities can cause fluctuations in the

No abstract is available for this article.

An ionogram is a graph of the time that a vertically transmitted wave takes to return to the earth as a function of frequency. Time is typically represented as virtual height, which is the time divided by the speed of light. The ionogram is shaped by making a trace of this height against the frequency of the transmitted wave. Along with the echoes of the ionosphere, iono- grams usually contain a large

Due to the inherent broadcast nature of wireless communication systems, instances of radio jamming are common, such as natural interference and man-made interference, resulting in increasing demands for radio monitoring. A spectrum monitoring method based on a generative adversarial network (GAN) model that is one of the most promising approaches of learning any kind of data distribution using unsupervised

The Waves instrument aboard Juno is a sophisticated radio astronomy observatory investigating Jupiter’s auroral radio emissions and plasma wave interactions. Waves records electric field properties using two monopole antennas, which are connected to form a dipole. The receiving properties of the Waves dipole changes quite remarkably over the instrument’s frequency range from near DC to 40 MHz. In this

We present the first results on E region field-aligned irregularities (FAIs) observed using a 53 MHz radar experiment conducted from Ionosphere Field Station, Haringhata (geographic latitude 22.93°N; geographic longitude 88.5°E; magnetic dip angle 35.2°N) of University of Calcutta, a location just on the Tropic of Cancer and below the Equatorial Ionization Anomaly. Results show that the E region FAI

Equatorial plasma bubble (EPB) irregularities are large-scale plasma depleted structures that exist in the equatorial and low-latitude ionosphere. Thus, particularly in these regions, much attention must be given to the effects of the EPBs in the life critical applications based on global navigation satellite systems (GNSS). The study on the dynamics of plasma bubbles, particularly in the determination

In this paper, new bridged-T network operating with bandpass (BP) negative group delay (NGD) function is introduced. The circuit design is innovatively based on an inductorless passive RC-network. The innovative bridged-T topology is implemented with a R-shunt configuration. The analytical transfer function of voltages and equivalent impedance-matrix are carefully calculated. The BP NGD analysis and

The Deployable Low-Band Ionosphere and Transient Experiment (DLITE) is a four-element interferometric radio telescope made from mostly commercial off-the-shelf parts to minimize costs and maximize ease of deployment. It operates in the high frequency and very high frequency (VHF) regimes, nominally in a 30–40 MHz band, but with good sensitivity (sky-noise dominated) in the 20–80 MHz range. Its configuration

We investigate a novel way to quantify Very Low Frequency transmission in the Earth-Ionosphere Waveguide, using data from the World Wide Lightning Location Network (WWLLN). The lightning signals from intense and long-duration storm clusters are recorded at several stations. Any individual stroke amplitude is in principle unknown, so that the recorded electric field from that stroke varies semi-randomly

Slant absolute total electron content (TEC) is observed by the Formosa Satellite-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (FORMOSAT-7/COSMIC-2, F7/C2) Tri-GNSS Radio Occultation System (TGRS) instrument. We present details of the data processing algorithms, validation, and error assessment for the F7/C2 Global Positioning System (GPS) absolute TEC observations. The

The characteristics of plasma waves propagating in the Earth’s plasmasphere and magnetosphere are important in terms of understanding the plasma environment in which these waves are excited and propagate. The propagation direction is a critical in propagation analysis of ELF/VLF band waves. The Means, eigenvector, amplitude, and SVD methods have been proposed previously to estimate the direction of

Artificial ionospheric hole created by the release of neutral gases (such as sulfur hexafluoride) has a significant impact on the propagation of radio waves. Based on the ray-tracing method, the propagation patterns of HF radio waves in the ionospheric hole and the characteristics of its echoes are discussed in this paper. The results show that the HF waves will be deflected and bended while passing

Electromagnetic (EM) fields in the extremely low-frequency (ELF) domain that can be excited by the vertical electric dipole (VED) and propagated in the Earth-ionosphere spherical cavity have received tremendous attention owing to their exploitation in many fields such as communication, earthquake prediction, and geophysical investigations. Some researchers use the planar model and curvature correction

This paper investigates a negative group delay (NGD) design of Ulu geometrical shape circuit. The NGD basic topology is constituted by a coupled line coupler with two-port terminated by open-ended stub. The S-matrix model of the topology is presented. The design equations allowing to determine the NGD circuit parameters in function of the NGD function specifications, NGD center frequency, NGD values

Fast and accurate solution has been derived to the electromagnetic (EM) scattering problem from a dipole antenna placed on a planar multi-layered earth. The derivation consists of three steps. First, reducing the field integrals to combinations of recognized Sommerfeld integrals (SIs) and expressed it as an infinite series. Next, in the complex - plane, we replaced the reflection coefficient by using

Precise transfer of time and frequency signals over long distances as well as clock synchronization to an ultra-stable reference are very crucial for many of the technological applications as well as for advanced scientific research. These reinforces a wide range of applications such as navigation, power grid management, mobile communication, and so on. In order to compare the performances of two highly

The atmospheric measurements made by the eight Mars orbiters in operation (as of April 2021) significantly improved our understanding of the Martian weather and climate. However, while some of the existing Mars orbiters will reach their lifetime, innovative and cost-effective observation concepts are requested – not only to guarantee continued observation but also to address potential gaps in the existing

No abstract is available for this article.

Modeling forest propagation loss over a vast area is challenging, particularly for the hilly terrain regions where canopy obstacle depth varies with region. To consider such vegetation impact, we present a novel forest cover classification well-defined with the line-of-sight (LoS). Furthermore, we incorporated the mobile antenna site elevation angle, which showed significant influence within the target

A unified approach is developed for the analysis of singularities of the scattered field and vanishing of scattering harmonics. Rigorous proofs are presented of the existence of complex resonance singularities of the solution to the problem of the plane wave scattering by a circular homogeneous dielectric cylinder. The method employs a mathematically correct approach of the spectral theory of open

In this paper we present the results of an inversion of ionospheric phase scintillation data to characterize the plasma density irregularity parameters for the structures associated with a series of Polar Cap Patches. The parameter estimates obtained during the inversion suggests that the irregularities associated with Polar Cap Patches are predominantly composed of moderately elongated electron density

Phase unwrapping is very important to acquire surface deformation using InSAR, unwrapping the interferometric phase directly is not appropriate because the phase is affected by various noises. Therefore, it is essential to apply a suitable filter to the interferometric phase before phase unwrapping. Although there are many filtering methods for noise, these methods cannot be used directly due to the

This study aims to evaluate the performance of phase-locked loop (PLL) under the presence of distinct scintillation patterns in the signal. Scintillation is very common in low-latitude regions due to the ionospheric dynamics. Under strong scintillation scenario the occurrence of deep fading events is usually registered and may cause severe degradation in the communication. The investigation conducted

No abstract is available for this article.

Among the techniques for atmospheric sounding, radio occultation enables an in depth investigation of vertical profiles from the ionosphere to the troposphere by measuring the radio frequency signal associated to the propagation medium. A precise characterization of the atmospheric layers requires a thorough processing of the raw radio tracking data to estimate the thermodynamic properties of the atmosphere

The Global Positioning System (GPS) cycle slip has a marked impact on the application of communication and navigation systems and therefore is one of the main concerns of the user and designer of terminal systems. In this study, we analyzed the temporal and spatial characteristics of cycle slip events using the GPS data detected from 260 observations in the China sector during the period of the year

This paper describes the development of superconductor–insulator–superconductor (SIS) receivers in the 787–950 GHz radio frequency (RF) range, which covers the highest frequency band of the Atacama Large Millimeter/submillimeter Array (ALMA) and is recognized as the most difficult band in terms of superconducting technology, because the conventional superconducting material of Nb cannot be used for

Obtaining high‐precision Doppler frequencies for very weak and high‐dynamic signals in deep space exploration is challenging. Such signals are commonly encountered, including in soft landing of lunar probes and the entry, descent, and landing (EDL) phase of Mars probes. Phase‐locked loop (PLL) is a widely used method for measuring high‐precision Doppler frequencies. In this study, two major improvements

The dual‐frequency global positioning system (GPS) data acquired from the UNAVCO over different places of Nepal were processed to examine the eclipse‐triggered consequences on total electron content (TEC) in response to the annular solar eclipse of 15th January 2010 and 21st June 2020. These occasions were exceptional since they occurred during solar minimum, additionally as in a magnetically quiet

Massive Multiple‐Input Multiple‐Output (MIMO) is emerging as one promising technology for the fifth generation (5G), but the hardware and software complexity arising from the sheer number of transmitting elements is a bottleneck. Antenna selection strategies have been reported as an appealing solution for hybrid beamforming architectures to select a number of radio‐frequency (RF) chains less than the

A new method is developed to retrieve electron density profiles from a raw virtual height ionosonde traces. A Kalman filter is used for the assimilative inversion scheme together with the newly developed data‐driven vertical covariance model. The detailed mathematical formalism for the derivation of the Jacobian that takes into account the effect of the magnetic field is presented. The incoherent scatter

In this study, we use a collection of Gaussian striations to generate random realizations of a disturbed ionosphere. The formalism is developed here to create a two‐dimensional realization of electron density by summing a large number of Gaussian striations, uniformly distributed in space and with a given probability density function of their radii. We analytically calculate the power spectral density

Radar and jammer can be considered as two players in the countermeasure game of electronic warfare (EW). A game framework for joint beamforming and power allocation is investigated for multistatic radars and multiple jammers in this paper. Under a certain target detection criterion, the major aim of every radar is to reduce its power consumption and suppress various jammings. Conversely, the multi‐agent

Incoherent scatter radars (ISR) are among the most powerful ground‐based instruments for solar‐terrestrial physics, measuring multiple plasma parameters over almost the entire vertical extent of the ionosphere. In Sanya, on Hainan Island, China, an advanced high‐power phased array ISR, known as the Sanya incoherent scatter radar (SYISR), is under construction. A tristatic system is planned, with a

The Agile Dual Auroral Radar Network (AgileDARN) radar has been developed as an all‐digital high‐frequency (HF) coherent scatter radar. Based on phased array antenna and digital signal processing techniques, digital beam forming (DBF) is employed for both transmission and reception, which steers toward the desired direction based on the relative phases within the array elements. However, the amplitude

In radio astronomy, holography is a commonly used technique to create an image of the electric field distribution in the aperture of a dish antenna. The image is used to detect imperfections in the reflector surface. Similarly, holography can be applied to phased array telescopes, in order to measure the complex gains of the receive paths of individual antennas. In this paper, a holographic technique

No abstract is available for this article.

In this paper, a comprehensive view of the evening and nighttime ionospheric irregularities using Communication/Navigation Outage Forecasting System (C/NOFS), Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), and Global Navigation Satellite System GPS satellites were carried out over the east African region during June and September 2014. The strength of the pre‐reversal

ULF magnetic anomalies (f < 1 Hz) have been observed prior to multiple large earthquakes (EQs) during the last three decades. A polarization analysis method was produced and applied in many EQ cases in order to discriminate the weak ULF crustal signals from other signals. Although many publications considered the parameter of polarization ratio (amplitude or power ratio of vertical magnetic field component

High frequency (HF) radio waves propagating through regions of ionospheric plasma irregularities exhibit random fluctuations in both amplitude and phase referred to as scintillations, which heavily influences the detection performance of HF sky‐wave radar and hybrid sky‐surface wave radar systems. In this paper, a numerical multiple phase screen model for HF sky‐wave propagation is developed, which

Forty years of studies on bioelectromagnetics, in our laboratory, are presented to view new horizons in electromagnetics in medicine and biology. The several topics are reviewed and discussed. The review includes transcranial magnetic stimulation (TMS) of the human brain, imaging of electrical information in the brain based on magnetic resonance imaging (MRI) such as impedance MRI and current MRI,

This paper presents a comprehensive analysis of results obtained using NWRA’s assimilative ionospheric model GPSII when it is driven by Spire Global, Inc.’s global navigation satellite system ‐ radio occultation (GNSS‐RO) measurements. Results of the assimilative model are validated using the database of Digisonde and Dynasonde ionograms. A week’s worth of dual‐frequency phase data was collected from

This study investigates an innovative theory on design of dielectric resonator (DR) based negative group delay (NGD) microwave circuit. The NGD circuit is mainly constituted by a cylindrical bulk of DR as a coupling element with a microstrip line. The developed theory is analytically established from the S‐parameters modeling of this innovative DR NGD topology. The NGD analysis and synthesis equations

In this paper, a novel and simple dual-polarized frequency-selective rasorber (FSR) which has a wide absorption band including a wide transmission band was presented. Detailed equivalent circuit was derived to accurately predict the frequency responses of the structure. Based on reasonable equivalent analysis of a traditional metal grid structure, a modified structure with improved performance was

The editors thank the 2020 peer reviewers

The present study explores the center‐of‐mass (Hc) of the ionosphere as the effective ionospheric varying shell height (VSH). We presents global ionospheric maps GIM‐Hc produced with IRI‐Plas model by assimilating the instant GIM‐TEC maps provided by JPL from 1994 to present which allows obtaining global maps of the F2 layer critical frequency, GIM‐foF2 (or NmF2) and peak height, GIM‐hmF2. Ratio TEC/NmF2

No abstract is available for this article.

An inverse problem of reconstructing real permittivity of a plane‐parallel layer in a perfectly conducting rectangular waveguide or in free space from experimental data using an explicit expression for the scattering matrix is considered. In general, this problem is improperly posed and may be unsolvable due to inaccuracy of the experimental data, and for a perfect noiseless experiment the solution

The Ionospheric Continuous‐wave E‐region Bistatic Experimental Auroral Radar (ICEBEAR) is a VHF coherent scatter radar that operates with a field‐of‐view centered on 58°N, 106°W and measures characteristics of ionospheric E‐region plasma density irregularities. The initial operations of ICEBEAR utilized a wavelength‐spaced linear receiving array to determine the angle of arrival of the ionospheric

Refractivity‐from‐clutter (RFC) is a technique for remote sensing of the lowest portion of vertical atmospheric refractivity profile, particularly evaporation and surface‐based ducts. It uses the sea‐surface backscattered radar signal to estimate the ducting conditions. The Lower Atmospheric Propagation (LATPROP) radar is a software‐defined, coherent‐on‐receive remote sensing system built on a low‐cost

This manuscript presents a rectenna with a high impedance asymmetric antenna array for ambient wireless energy harvesting at the 2.45 GHz frequency band. It is fulfilled without using any impedance matching networks, which demonstrations significant benefits over available rectennas as a function of the layout and cost with a wide range of input power level and load impedance. A rectenna prototype

This two‐part article presents a review of different techniques of mutual coupling (MC) reduction. MC reduction is a primary concern while designing a compact multiple‐input‐multiple‐output (MIMO) antenna where the separation between the antennas is less than λ0/2, that is, half of the free‐space wavelength. The negative permittivity and permeability of artificially created materials/structures (Metamaterials)

This two‐part article presents a review of different techniques of mutual coupling (MC) reduction. MC is a major issue when an array of antennas is densely packed. When the separation between the antennas is <λ0/2, i.e., half of the free‐space wavelength, the antenna parameters suffer from the surface wave, and the space wave coupling effect between the antenna elements. To reduce the MC influence

Japanese space weather research and operation began in 1896 with research on radio propagation. LF, MF, and HF radio communication used to be important before the era of communication satellites; however, they are affected by ionospheric conditions and solar activity. A center for the research and development of radio systems was established at Hiraiso, which is now also a space weather observatory

The results of theoretical studies and mathematical modeling indicate the possibility of obtaining the angular superresolution and its limits by using algebraic methods of imaging. The necessary algorithms are created on the basis of solution to inverse problems. The limiting levels of the achieved angular superresolution are found depending on the signal‐to‐noise ratio for objects of various types

During the guidance of the missile, the target needs to be positioned in real time. The detonating missile will look forward to the target area during the flight, and the imaging distance becomes closer as the missile approaches the target. The image quality of forward‐looking missile‐borne bistatic synthetic aperture radar (FM‐BSAR) deteriorates rapidly when the detonator enters a rapid dive stage

No abstract is available for this article.