High Frequency Radio Waves Research Articles

Monitoring of Ionospheric Variability Using the Low lAtitude Long Range Ionospheric raDar (LARID): Capabilities, Advantages and Limitations

AbstractA Low lAtitude long Range Ionospheric raDar (LARID), which was built recently at Dongfang (19.2°N, 108.8°E, magnetic latitude 13.9°), Hainan Is., China, is employed to study the ionospheric variability over a large region. The LARID consists of two high frequency (HF) coherent backscatter radars, looking toward east and west, respectively, with a field‐of‐view covering a wide longitude from Africa to Pacific. Here we report some results by the LARID, with main focus on its capabilities, advantages and limitations in monitoring ionospheric variability. The results show that the LARID can detect various ionospheric variations at low latitudes, including (a) sequentially generated equatorial plasma bubbles over a longitude span of ∼80°, (b) near‐range E region irregularities drifting across more than 1,000 km, (c) ionospheric background information retrieved from ground scatters, (d) traveling ionospheric disturbances, and (e) sporadic E structures reflecting HF radio waves at low elevation angles. It is demonstrated that the LARID provides an important tool for investigating different types of ionospheric variability over a broad region, especially over the Indian Ocean and west Pacific, and will contribute significantly to the regional ionospheric weather forecasting.

Differential Delay of Ordinary and Extraordinary Modes of Transionospheric Radio Waves

AbstractThe terrestrial ionosphere is a birefringent medium that allows radio waves to propagate in two modes: the ordinary (O‐mode) and the extraordinary (X‐mode). A difference in the index of refraction of the two modes results in differential delay (mode delay) between the O‐ and X‐modes of radio waves propagating through the ionosphere. Mode delays of transionospheric high frequency radio waves are determined using the Radio Receiver Instrument (RRI) onboard the Enhanced Polar Outflow Probe (e‐POP) on the CASSIOPE/Swarm‐E satellite. Experiments between RRI and the SuperDARN radar at Saskatoon, Canada show large variabilities in mode delays. The mode delays are nearly constant in some experiments but other experiments have large variations. The mode delay observations could not be explained by the distance between the e‐POP satellite and the radar, the foF2 values along the satellite track, nor whether the satellite track was across or along a SuperDARN radar beam. A combination of RRI observations and ray‐trace modeling are used to investigate the mode delay of transionospheric radio waves.

A Near-Real-Time Forecasting Model of High-Frequency Radiowave Propagation Factor Fusion Based on the ICEEMDAN Decomposition and Bi-LSTM Methods

A Near-Real-Time Forecasting Model of High-Frequency Radiowave Propagation Factor Fusion Based on the ICEEMDAN Decomposition and Bi-LSTM Methods

High‐Latitude Off‐Great Circle Propagation Associated With the Solar Terminator

AbstractLarge‐scale ionospheric gradients associated with the solar terminator can deflect high frequency (HF) radio waves to off‐great circle paths during the morning and evening, negatively impacting technologies reliant on HF radio wave propagation. For example, geolocation algorithms used by scientific and military over‐the‐horizon radars (OTHRs) generally assume on‐great circle propagation, and thus lateral deviations from the great‐circle path can lead to positioning errors. In this study, radio wave propagation is simulated via 3D numerical ray traces though an empirical, high‐latitude model ionosphere initialized for a variety of times of the day and year to explore and quantify high‐latitude off‐great circle propagation associated with the solar terminator. Analysis of these simulations show large scale east‐west ionospheric gradients due to the solar terminator can cause lateral deviations in north‐directed propagation paths exceeding 20° at sunrise and sunset depending on radio wave frequency, though the largest portion of received signal power tends to experience maximum deflections of 5°. An exploration of the dependence of propagation direction on deflection shows that propagation paths parallel to the solar terminator tend to experience the largest deflections. Since the solar terminator at high latitudes is at an angle with respect to north in the winter and summer, propagation paths oriented west or east of north can experience larger deflections than north oriented paths at sunrise and sunset during these times of year. Impacts of these diurnal deflections on the operation of OTHR and scientific radar are discussed, as well as possible strategies for mitigating them.

The Ellipticity of High Frequency Transionospheric Radio Waves

AbstractThe polarization state of transionospheric high frequency (HF) radio waves can be determined using the crossed‐dipole antennas of the Radio Receiver Instrument (RRI) onboard Enhanced Polar Outflow Probe (e‐POP) on the CAScade, Smallsat, and IOnospheric Polar Explorer/Swarm‐E satellite. Coordinated experiments between ground radars and RRI showed that the radio waves have high ellipticity angles (elliptical or circular polarization) for propagation direction 6°–25° from the perpendicular direction to the local geomagnetic field. However, from magnetoionic theory and a typical assumption of roughly equal power in the O‐ and X‐modes, radio waves can have high ellipticity angles only when the propagation direction is within 10° of perpendicularity. This investigation uses coordinated experiments between the Saskatoon SuperDARN radar and RRI. Magnetoionic modeling reveals that the relative strengths of the O‐ and X‐modes for the HF radio waves transmitted from the Saskatoon SuperDARN change significantly poleward of the radar. Differences in the relative power between the two wave modes were found to significantly modify the polarization state of radio waves, and govern the sense of rotation of the wave. Even a relatively modest 2–5 dB power difference in the X‐mode over the O‐mode was found to result in unexpected observations of circularly polarized radio waves at aspect angles 6°–10° from perpendicular, and unexpected elliptically polarized waves observed at aspect angles more than 10° from perpendicular. Therefore, a combination of RRI observations and modeling, which accounts for relative differences in the O‐ and X‐mode powers, was used here to better understand the unexpected observations of polarization states of transionospheric radio waves.

Statistical Analysis of Off‐Great Circle Radio Wave Propagation in the Polar Cap

AbstractHigh latitude ionospheric density structures such as polar cap patches and arcs are capable of deflecting high frequency (HF) radio waves to off‐great circle paths, and are likely detrimental to technologies dependent on HF radio propagation. In this study, nearly 2.5 years of 4.6–14.4 MHz data from a multi‐frequency HF radio link between Qaanaaq, Greenland and Alert, Canada are used to investigate high‐latitude off‐great circle propagation in the polar cap. After an example of HF radio propagation affected by polar cap patches is shown in detail, a statistical analysis of the occurrence and impacts of off‐great circle deflections in the polar cap is presented. Off‐great circle propagation is shown to be increasingly common with increasing frequency up to 11.1 MHz, such that averaged over 1 year, received 11.1 MHz signals experienced deflections >30° from the great circle direction 65.6% of the time. The occurrence of these deflections across the year is shown to be at a maximum in the winter, while occurrence across the day varies with season. Trends across both time of day and time of year for 11.1 and 14.4 MHz deflections are consistent with polar cap patch occurrence trends. Off‐great circle deflections are shown to be associated with increased time‐of‐flights, a larger range of positive and negative Doppler shifts, increased Doppler spreads, and lower signal‐to‐noise ratios. These results are discussed in the context of ionospheric phenomena in the polar cap, and implications for over‐the‐horizon radars operating at high latitudes.

Anomalous Long‐Distance Propagation of ILS LOC Signals by the Es Layer and Its Impact on Aviation Receivers

AbstractAnomalous long‐distance propagation of Very High Frequency radio waves of aeronautical navigation systems was investigated by an airborne Instrument Landing System (ILS) localizer (ILS LOC) receiver installed on the ground at Kure, Japan (34.245°N, 132.528°E). Intense ILS LOC type signals were observed and the received power was strong enough for the aviation receiver to output course deviation. The radio source was identified by receiving the Morse Code for identification as the localizer‐type directional aid (LDA) serving the Runway‐21 of the Hualien Airport, Taiwan (24.0396°N, 121.6221°E) of which beam pointed close to the receiver. This result supports that the source of the signals often observed at the same frequency at the same location is most probably the LDA at the Hualien Airport. The maximum received power was −99 dBm for an omni‐directional antenna. It was strong enough to cause co‐channel interference. Considering stronger power (−70 dBm) found in previous observations at the same frequency at the same location, anomalous propagation of ILS LOC signals by the Es layer could be a cause of interference when a receiver was near the center of the ILS LOC beam. The course deviation output was consistent with the geometry between the beam of Runway‐21 LDA at the Hualien Airport and the receiver. However, the observed course deviation fluctuated remarkably even when the received power was strong enough. The fluctuation of the course deviation may indicate the structure of the Es layer, and observation of the course deviation could be used to diagnose the Es layer structure.

An Updating of the IONORT Tool to Perform a High-Frequency Ionospheric Ray Tracing

This paper describes the main updates characterizing the new version of IONORT (IONOsperic Ray Tracing), a software tool developed at Istituto Nazionale di Geofisica e Vulcanologia to determine both the path of a high frequency (HF) radio wave propagating in the ionospheric medium, and the group time delay of the wave itself along the path. One of the main changes concerns the replacement of a regional three-dimensional electron density matrix, which was previously taken as input to represent the ionosphere, with a global one. Therefore, it is now possible to carry out different ray tracings from whatever point of the Earth’s surface, simply by selecting suitable loop cycles thanks to the new ray tracing graphical user interface (GUI). At the same time, thanks to a homing GUI, it is also possible to generate synthetic oblique ionograms for whatever radio link chosen by the user. Both ray tracing and homing GUIs will be described in detail providing at the same time some practical examples of their use for different regions. IONORT software finds practical application in the planning of HF radio links, exploiting the sky wave, through an accurate and thorough knowledge of the ionospheric medium. HF radio waves users, including broadcasting and civil aviation, would benefit from the use of the IONORT software (version 2023.10).

Duration and extent of solar X-ray flares and shortwave fadeouts likely to impact high frequency radio wave propagation based on an evaluation of absorption at 30 MHz

High frequency (HF; 3–30 MHz) radio wave propagation can be impacted by absorption that results from enhanced photoionization in the dayside D-region following a solar X-ray flare. A database of >25,000 solar X-ray flares was evaluated to characterize the relationship between flare duration and the peak of the 0.1–0.8 nm solar X-ray flux. Expressions describing the mean and 90th percentile duration were developed. Based on these models, mean durations of 13, 18, 27, and 39 min and 90th percentile durations of 30, 48, 77, and 123 min are expected for C1, M1, X1 and X10 solar X-ray flares, respectively. A probability distribution of flare durations was developed to describe the probability of flare duration lasting 0–15, 15–30, 30–45, 45–60, 60–90, >90 min. In addition to flare duration, the duration of the expected impact to HF radio waves was evaluated. By considering examples where HF radio wave propagation in the 5–15 MHz range was impacted by space weather, a 0.5 dB threshold at 30 MHz was observed in samples of riometer data. Absorption modelled at 1-min increments from 1986 to 2017 was evaluated to create a probability distribution of impact duration, defined as the length of time the modelled 30 MHz absorption exceeded 0.5 dB during a single event. Modelled absorption was further evaluated to demonstrate the geographic extent of enhanced absorption, and to determine the minimum solar X-ray flux required to exceed the 0.5 dB impact threshold at a given latitude as a function of solar zenith angle and time of year. The results of this paper provide a better understanding of the impact of solar X-ray flares on high frequency radio wave propagation and aid in the development of tools and services for mitigating space weather impacts to systems that rely on HF radio wave propagation.

Radio Wave Energy Harvesting Model of a Maritime Automatic Identification System

Radio waves, the spectrum of the electromagnetic waves, are all around us and in most cases have only one purpose. The maritime Automatic Identification System (AIS) uses Very High Frequency (VHF) radio waves for the purpose of data exchange between ships and shore stations. These data exchanges take place during certain time intervals, resulting in intermittent emission of electromagnetic waves. In the research presented in this paper, the objective was to add a new purpose for the AIS electromagnetic waves, i.e. to act as a power source for the RF energy harvester. After collecting the electromagnetic waves of the AIS system, the signals’ voltage is rectified, amplified and delivered to the load. In this paper, the process of radio wave energy harvesting is simulated in the Multisim software and analyzed in detail. The results of the analysis showed a multiple increase in the voltage value at the output of the RF energy harvester.

Outcomes of Treatment of Eyelids and Third Eyelid Tumours in Dogs Using High-Frequency Radiowave Surgery.

In human ophthalmology, the benefits of using high-frequency radiowave (HFR) electrocautery for surgical procedures were demonstrated and include effective haemostasis, shorter surgery times, and rapid recovery. In canine eyelid surgery, intraoperative bleeding is a common feature that may obscure the surgical field view and lead to the increased swelling of adjacent tissues, bruising, and pain. To evaluate the efficacy and benefits of HFR electrocautery in canine eyelid and third eyelid surgery, the medical records of 48 surgical excisions of eyelid tumours (involving up to one-third of the eyelid length) and 4 third eyelid excisions were reviewed. The information was collected including the breed, age, clinical signs, HFR power setting and mode of the surgical unit, electrode used for the surgery, intraoperative complications, histopathological diagnosis, and postoperative outcomes. Surgical techniques were performed using the Surgitron Dual 3.8 MHz Frequency RF device (Ellman International, Oceanside, NY, USA). Intraoperative bleeding was recorded as absent or very mild, and the surgical procedures were very fast. No complications occurred during the procedures. Healing within 10 days was observed in all the dogs. No tumour recurrences were recorded at the 12-month follow-up. HFR electrosurgery proved to be a safe, effective, and easy-to-perform technique for the removal of eyelid and third eyelid tumours in dogs.

Diffraction Theory of Propagation of High-Frequency Radio Waves in a Spherically Layered Ionospheric Radio Channel

Diffraction Theory of Propagation of High-Frequency Radio Waves in a Spherically Layered Ionospheric Radio Channel

WIRELESS NETWORKS IN DAY TODAY LIFE

Wireless networking has very important features as it offers firm and user’s flexibility, and portability with in the budget. It allows the users to get access to the network without the physical wired tied between them. It uses high frequency radio waves to communicate between devices. Technology is no longer judged by its technical brilliance, but by the return on investment. Wireless Networks fit into this because the technology has been around long enough and can provide enough benefits to be seriously considered for deployment. Mobility is another feature by wireless. This leads to other provision of wireless, that of scalability. It really helps in extending your network. It also becomes important if an enterprise has a rented office and needs to shift to a new place. Wi-Fi, or wireless fidelity, is freedom: it allows you to connect to the internet from your couch at home, a bed in a hotel room, or a conference room at work without wires. It is a wireless technology like cell phones, Wi-Fi enabled computers send and receive data indoors and outdoors; anywhere within the range of the base station. And the best thing of all, Wi-Fi is fast. In fact, it’s several times faster than the fastest cable modem connection. Wireless networks have seen unprecedented rise in their size and number of users in recent years. This unprecedented rise is attributed to the rise in the number of mobile computing devices. More over the amount of data that is handled by these wireless networks has increased in recent years. This increase in the flow of data over these wireless networks is due to increase in popularity of cloud computing, which is built on the concept of Software as a Service, where in all the data processing happens on the cloud. KEYWORDS: Wireless network , wi-fi , technology

Deep Electron Density Depletion Near Sunset Terminator on St. Patrick's Day Storm and Its Impacts on Skywave Propagation

AbstractThe plasma density distribution in the equatorial and low latitude ionosphere can often be severely disturbed during active space weather events that can have paramount impacts on the long‐distance high frequency (HF) radio wave (Skywave) communications through the ionosphere. On the St. Patrick's Day storm of 17 March 2015, a deep depletion of plasma with more than two orders of magnitude was observed over a narrow longitudinal sector near the sunset terminator. The controlled SAMI2 (Sami2 is Another Model of the Ionosphere) simulations indicate that a large equatorial vertical drift around sunset terminator can produce such a deep electron density depletion and strong reinforcement of equatorial ionization anomaly. The impacts of these ionospheric density disturbances on the Skywave communication systems have been investigated using an HF propagation simulator that solves the propagation path of radio waves under given background ionospheric conditions. The results clearly demonstrate that the usable HF spectrum for Skywave communications is reduced by more than 50% over the region of depletion. Further, large areas of skip zones, where the Skywave signals are not receivable, are produced due to low ionospheric densities over this region. This study can have important applications in the planning and operation of Skywave systems during the active space weather periods.

Acute Exacerbation of Conjunctival Papilloma after High-frequency Radio Wave Electrosurgery for Conjunctivochalasis: A Case Report.

Acute Exacerbation of Conjunctival Papilloma after High-frequency Radio Wave Electrosurgery for Conjunctivochalasis: A Case Report.

Simple surgical punctal occlusion with high frequency radiowave electrosurgery

BackgroundTo introduce and evaluate the efficacy of a simple punctal occlusion technique for dry eye patients.MethodsMedical records of 79 eyes from 40 patients refractory to common dry eye conservative treatment who underwent multiple high-frequency radio-wave electro-punctal occlusion were retrospectively reviewed. Pre- and post-procedural ocular surface indices (Schirmer test, tear break-up time (TBUT), and corneal staining grade (Oxford scheme)) and subjective symptom scores (including frequency of artificial tear use, interval between procedures, and total repeat time) were analyzed.ResultsAverage Schirmer test result was significantly (P < 0.05) improved from 4.10 ± 1.39 mm to 8.14 ± 3.13 mm at 6 weeks after the procedure (n = 79). A total of 32 eyes from 16 patients underwent repeated procedure with a mean interval of 8.00 ± 4.86 months, while 24 patients had a single procedure. Twenty-five of 30 patients showed improvement for subjective symptom scores. No complications related to the procedure were observed.ConclusionsA simple, less-invasive punctal occlusion technique using a fine-needle tip with high-frequency radio-wave could significantly relieve subjective symptoms and improve ocular surface indices of patients with aqueous deficient dry eye without causing a major complication. This procedure may play a considerable role in treating dry eye refractory to common practices.

Simulation Research on the Influence of Plasma Bubbles on Radio Wave Propagation

AbstractPlasma bubbles are large‐scale irregular structures that often occur at equatorial latitudes, equatorial plasma bubbles (EPBs) affect the propagation of high‐frequency (HF) radio waves. Based on their main observational characteristics, a three‐dimensional (3D) model of EPBs was established, and a preliminary simulation of EPBs was performed. Three‐dimensional ray tracing can be used to simulate HF radio wave propagation. In this study, we consider EPBs at different scales, appearing at different times and different heights, and investigate the influence of EPBs on the propagation path of radio waves at low latitudes. The simulation results show that when they propagate through EPBs of different scales, the propagation paths of radio waves are completely different. Radio waves at 6, 8, and 10 MHz show obvious refraction; With an increase in EPB scale, the focusing effect of radio waves will diminish, and the focusing height will increase. The propagation of HF radio waves through EPB change with time as follows: partial penetration, partial reflection, and total penetration, the refraction effect of EPB on radio waves gradually decreases over time. When radio waves propagate through EPB at different heights, the simulation results show that EPB at an altitude of 200 km makes little impact on the radio waves. As the height of EPB increases, the radio waves will exhibit significant refraction, showing an obvious focusing effect.

Global Simulations of Multi‐Frequency HF Signal Absorption for Direct Observation of Middle Atmosphere Temperature and Composition

AbstractThis paper presents the first numerical study on a new concept for the direct measurement of D‐region absorption in the high‐frequency (HF) band. Numerical simulations based on the Appleton‐Hartree and Garrett equations of refractive index are presented. Electron temperature as a result of HF radio pumping of the ionosphere is included in the calculations using proper numerical formulation. Both O‐ and X‐mode radio wave polarizations are taken into consideration. A global map of HF absorption in the northern hemisphere is calculated. Detailed calculations of HF radio wave absorption as it propagates through the lower atmosphere are presented. The effect of several parameters on the amount of absorption is calculated. The best frequencies to be used for the purpose of this study are discussed. A machine learning model is developed and the capability of the model in estimation of D and E‐region constituents includes N2, O, O2, as well as T and Ne is examined. Such a technique can also lead to global mapping of HF absorption and improve OTHR (over‐the‐horizon‐radar) performance.

Seasonal Variation in Land and Sea Surface Backscatter Coefficients at High Frequencies

Over the horizon radars (OTHR) rely on the propagation of high frequency (HF) radio waves via the ionosphere to successfully achieve their designated missions. Backscatter sounders (BSS) are environmental over-the-horizon radars which may be used to assess the ionospheric propagation conditions. However, high power observed by a BSS may be due to either good ionospheric propagation, a high surface backscatter coefficient, or a combination of both. Hence, an understanding of the surface backscatter coefficients and their temporal variation is essential to fully understand the ionospheric propagation conditions. A database of surface backscatter coefficients over a decade was created using backscatter ionogram data from four backscatter sounders in Australia. The temporal variations in the backscatter coefficients were investigated and it was found that the land backscatter coefficients were relatively constant over time, while the sea backscatter coefficients showed significant seasonal variation.

Occurrence Rates of SuperDARN Ground Scatter Echoes and Electron Density in the Ionosphere

AbstractGround scatter (GS) echoes in Super Dual Auroral Radar Network (SuperDARN) observations have been always expected to occur under high‐enough electron density in the ionosphere providing sufficient bending of high frequency radio wave paths toward the ground. In this study, we provide direct evidence statistically supporting this notion by comparing the GS occurrence rate for the Rankin Inlet SuperDARN radar and the F region peak electron density measured at Resolute Bay by the Canadian Advanced Digital Ionosonde and incoherent scatter radars RISR‐N/C. We show that the occurrence rate increases with roughly linearly up to about and the trend saturates at larger . One expected consequence of this relationship is correlation in seasonal and solar cycle variations of the GS echo occurrence rate and . GS occurrence rates for a number of SuperDARN radars at middle latitudes, in the auroral zone and in the polar cap are considered separately for daytime and nighttime. The data indicate that the daytime occurrence rates are maximized in winter and nighttime occurrence rates are maximized in summer for middle latitude and auroral zone radars in the Northern Hemisphere, consistent with the winter anomaly (WA) phenomenon. The effect is most evident in the North American and Japanese sectors, and the quality of WA signatures deteriorates in the European and, especially, in the Australian sectors. The effect does not exist in the South American sector and in the polar caps of both hemispheres.