Radio Frequency Range Research Articles

Divisional Load-Modulated Balanced Amplifier With Extended Dynamic Power Range

With the prevalence of complex modulated signals, it is of utmost significance to research the extension of the dynamic power range of radio frequency (RF) power amplifiers (PAs). This article proposes a divisional load-modulated balanced amplifier (DLMBA) for extending the high-efficiency power range. The proposed DLMBA is composed of a local modulated Doherty PA (DPA) and a class-C biased balanced PA (BPA) pair. The output signal of the local DPA is fed into the isolation port of the output coupler of the BPA pair, forming a global load modulation. The design parameters of the DLMBA are derived after a comprehensive analysis. It is illustrated that the dynamic power range of the DLMBA can be extended beyond 12 dB by combining a local DPA and a BPA pair. Meanwhile, each subamplifier of the DLMBA is presented with a modulated impedance over the whole dynamic power range, avoiding voltage oversaturation. As a validation, a DLMBA operating over 1.85–2.05 GHz is fabricated and measured in this article. The fabricated DLMBA delivers a maximum output power of more than 44.8 dBm, a saturation drain efficiency (DE) of more than 53%, and a 13 dB back-off DE of more than 44% in the interested frequency band. Meanwhile, when the DLMBA is excited by a 20-MHz wideband signal with a peak-to-average ratio of 10.2 dB, the measured adjacent channel leakage ratio reaches <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 47.4 dBc after digital predistortion.

Teratogenic effects of radiofrequency electromagnetic radiation on the embryonic development of chick: A study on morphology and hatchability

The present study was aimed at studying the effects of RF-EMR in causing teratogenic changes in the embryonic development of organisms using chick embryo as a model. The fertilized eggs of the hen were incubated in a digital humidified incubator and exposed to RF-EMR from 2G and 4G mobile phones by ringing at regular time intervals. The dose of RF-EMR was varied by increasing the call duration and number of calls per day, with the lower dose being a call duration of 50 min/day and the higher dose being 90 min/day. The phone kept had a range of radiofrequency between 900 and 1800 MHz and SAR (Specific Absorption Rate) 1.355 (2G) and 1.12 (4G) watts/ kg respectively. The batch of eggs incubated without any exposure to RF-EMR was taken as control. The hatchability of 2G and 4G experimental groups were respectively, 65% and 75% at lower radiation exposure and 40% and 55% at higher radiation exposure. The teratogenic effects of RF-EMR on the morphology of chick embryos manifested as the cross beak, non-retracted yolk sac, macrocephaly, malformed legs and toes, disability in standing and balancing the body and variations in body weight, body length and beak length. The results indicate that the RF-EMR poses potential threats to the developing stages of organisms.

The effect of 1H offset and flip-angle on heteronuclear decoupling efficiency in ROSPAC pulsed sequence: A Floquet description.

A new heteronuclear decoupling sequence for solid-state NMR and magic angle spinning faster than 60kHz was recently introduced [Simion et al., J. Chem. Phys. 157, 014202 (2022)]. It was dubbed ROtor-Synchronized Phase-Alternated Cycles (ROSPAC), and it offers robustness for a large range of chemical shifts and low radio-frequency (RF) powers and is almost independent of the radio-frequency power. Here, we theoretically explore the robustness of the ROSPAC sequence toward 1H offset and RF field inhomogeneities, as well as the spacing effect of the π pulses on the decoupling efficiency. We use a generalized theoretical framework based on the Floquet theory to assess these parameters. The optimum decoupling conditions, where the magnitude of the second-order cross-terms and first-order resonance conditions are small, were identified.

Detecting UAV Presence Using Convolution Feature Vectors in Light Gradient Boosting Machine

The growing number of Unmanned Aerial Vehicle (UAV) applications brings with it, a rising number of privacy concerns. The high availability of commercial drones is also increasing the need for strict regulations. As far away as we are from establishing such protocols to ensure that the most basic human right to privacy is not exploited, we are further away from enforcing them. Thus, there is a need for a generalised drone detection system to detect different drones operating in a broad range of Radio Frequencies (RF). Previous attempts to tackle this problem have been made using audio, video, radar, WiFi and RF signals. While all these methods have their own benefits and drawbacks, RF has various characteristics which make them suitable for practical applications on a large scale. In this paper, we propose a novel technique called the ConvLGBM model which combines the feature extraction capability of a Convolution Neural Network (CNN) with the high classification accuracy of the Light Gradient Boosting Machine (LightGBM). We develop and evaluate the classifications done by an optimal CNN and the LightGBM model and then compare both models with the ConvLGBM.

Safety of digital learning environment for the health of high school and university students in distance learning

The development of technologies using the electromagnetic field (EMF) of the radio frequency range has become a leading trend related to the need for wireless data transmission. This made it possible for distance learning of schoolchildren and students in a dangerous epidemic situation. Accumulated data on the sensitivity of the human body to the action of EMF. The purpose of the work is to assess the conditions of teaching schoolchildren in computer science classrooms, as well as the impact of online learning on the health of high school students and university students. Based on the results of an online survey of schoolchildren and students according to the author’s questionnaire, a database was formed and an assessment of the conditions of distance learning was carried out. With the use of instrumental research, an assessment of the learning conditions in computer science classrooms was carried out. The materials were processed using the reliability criterion χ2 and the health risk assessment RR. Control data in computer science classrooms showed non-compliance of temperature, air humidity, air ionization, illumination, noise with regulatory requirements, except for EMF levels. With online learning, a high duration of stay of high school students and students in a digital environment has been established, including the learning process, homework, and leisure time on the Internet. In the structure of complaints related to studying online and doing homework, there were: visual impairment over the past year, headaches, back pain, irritability, eye fatigue, a feeling of dryness in the eyes. The time for sleep and physical activity decreased. Data have been obtained confirming the need to protect the health of students in a digital environment with the provision of safe conditions for visual work, limiting the time of use of digital devices, increasing the literacy of all users.

A varactor-based 1024-element RIS design for mm-waves

This paper reports a reconfigurable intelligent surface (RIS) for beamforming and beam steering applications operating in the millimeter wave (mm-waves) frequency band. The proposed 2-bit RIS design is implemented using a radar cross-section (RCS) approach in ANSYS HFSS for performance evaluation and system-level analysis. It is based on split-ring resonator (SRR) unit cells, tuned by varactor diodes, comprising 1,024 elements arranged in a 32 × 32 matrix with linear gradient phase configuration operating at 24.5 GHz over the fifth generation of mobile communications New Radio (5G NR) frequency range 2 (FR2). A beam steering from −60° to 60° in the azimuth plane is demonstrated for mm-waves coverage extension. Numerical simulations of RCS patterns from −10° to −60° and from 10° to 60° with approximately 3 dB scan loss manifest the applicability of the proposed RIS towards the sixth generation of mobile communications (6G). Furthermore, simulated results of angular reciprocity prove the RIS response up to 110° under an oblique incident wave at 60°. To the best of our knowledge, this is the highest RIS angular reciprocity reported in the literature, validating its application to coverage extension from −60° to 60°. In addition, the RCS level and reflected angle relationship are modeled for system-level analysis purposes.

CHILDREN ARE MORE EXPOSED TO ELECTROMAGNETIC RADIATION IN COVID-19 LOCKDOWN: A LITERATURE REVIEW

Introduction: The COVID-19 pandemic has significantly affected people's quality of life. Unfortunately, the epidemic continues in various variants and it remains unclear how long it will continue. Children staying at home in the COVID-19 quarantine spent hours in front of the screen with online education. In addition, since they could not go out, they spent their free time in front of the screen using social media, playing computer games or watching movies. The aim of this study is to investigate the effects of low-level electromagnetic radiation (EMR) that children are exposed to at home during the COVID-19 quarantine. Method: The research method is literature review. Results: Studies have shown that, during the quarantine period, children's use of telecommunication devices such as televisions, tablets, smartphones and computers greatly increases. It was determined that the range of radio frequency (RF), Wi-Fi, power lines, visible light and Bluetooth increased in the home environment. The electric and magnetic fields emitted from these devices contain EMR and can seriously harm the health of children, who are structurally more sensitive than adults. Conclusion: There are growing concerns that children staying at home during the COVID-19 pandemic will face health hazards in the future as they are more exposed to EMR.

Dual-Band CMOS Low-Noise Amplifier Employing Transformer-Based Band-Switchable Load for 5G NR FR2 Applications

This letter presents a dual-band complementary metal–oxide–semiconductor (CMOS) low-noise amplifier (LNA) for fifth-generation (5G) new radio (NR) frequency range 2 (FR2) applications. The proposed design utilizes a transformer-based band-switchable load to tune resonance conditions in the 26–30- and 37–40-GHz bands. Through ON–OFF control of the transformer functionality, the primary inductance can be adjusted with lesser quality-factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor) degradation compared to the conventional direct inductor switching approach. The proposed design is implemented using a 65-nm CMOS process. At 28 and 39 GHz, respectively, the gains of 13.7 and 13.1 dB, noise figures (NFs) of 3.8 and 4.1 dB, input 1-dB compression points of −15.2 and −16 dBm, and input third-order intercept points of −7.15 and −6.85 dBm are realized. The implemented design draws a bias current of 11.6 mA with a 1-V supply.

Analysis of Three-Stage LNA Architecture for CMOS RF Front End

Wireless communication continues to lead the world. The term “wireless” significantly influences everything from telephone to satellite communication. Recent years have seen the need for appropriately built Low Noise Amplifiers (LNAs) in receiver front end because of the modem wireless communication in broadcast and microwave radio. In this paper a high performance LNA for the radio frequency range is presented. To achieve high gain a three stage LNA with each stage as Cascode stage is considered here. The simulation shows that the presented LNA has a gain of 26.12 dB and a Noise Figure (NF) of 2.6 dB. The achieved output and input returns losses are -8.4 dB and -11.6 dB respectively.

Cost efficient fabrication of flexible polymer metacomposites: Impact of carbon in achieving tunable negative permittivity at low radio frequency range

Cost efficient fabrication of flexible polymer metacomposites: Impact of carbon in achieving tunable negative permittivity at low radio frequency range

Развитие принципов контроля электромагнитной обстановки с учетом дозиметрических параметров

The article considers a possibility of improving the methods of controlling the electro-magnetic environment subject to additional parameters. There has been conducted analysis of the Russian and international standards on hygienic regulation of electromagnetic fields to reveal the parameters characterizing the interaction between the energy of an electromagnetic field and biological objects. A specific absorbed rate and a specific absorbed energy are quantitative characteristics of the interaction of electromagnetic fields with biological objects. The biological effects of electromagnetic radiation on the biological objects are considered. A promising direction for ensuring safety from the effects of electromagnetic radiation is a comprehensive methodology of monitoring and visualizing the electromagnetic environment. To improve the principles of monitoring the electromagnetic environment there have been considered the methods of dosimetry of electromagnetic fields of the radio frequency range. Theoretical dosimetry methods are based on the use of anatomically realistic computer models of typical biological objects, taking into account the values of electrical properties for different simulated biological tissues in the models. There have been shown the advantages and disadvantages of theoretical dosimetry methods based on computational methods: the finite element method, method of moments, multipolar method, hybrid methods and analytically based methods. Experimental dosimetry consists in direct measurement of the magnitude of the electromagnetic field energy of the emitting object. A modern system of experimental dosimetry of electromagnetic radiation for assessing the dosimetric parameters of the absorbed electromagnetic field energy is presented including measuring probes, a probe positioning system, a testing system, a method for measuring parameters, as well as a control and data processing system. The conducted research makes it possible to identify theoretical and experimental methods of dosimetry that can be used to control the electromagnetic environment, taking into account dosimetric parameters.

Research for self-reported health problems after excessive talking time on mobile phones among university students

The devices that people use every day, such as mobile phones and wireless networks, emit electromagnetic waves in the radio frequency range. The widespread use of these devices, as well as the change in people’s social behavior, have dramatically increased their exposure to electromagnetic radiation. Due to the rapid increase of young people users, public health officials and the scientific community are showing particular interest in the possible effects of electromagnetic radiation on human health. Many researchers express strong concerns about the effects of exposure to electromagnetic radiation, as it can have a serious impact on physical, cognitive, and social health. This study focused on self-reported health problems after excessive talking time on mobile phones of 619 (n=619) University students of both genders, in the age group of 18-24 years were randomly selected. The data was collected using a close-ended questionnaire. Headache was found to be the most frequently reported symptom (69%) followed by pressure in the head (38.8%). In most self-reported health problems no correlation was found between the genders. Female students tend to talk more on their mobile phones, and it was found that this extensive use was associated with the declaration of more self-reported health problems. The results of this study do not leave us any room for complacency, especially when we talk about health issues, and continuous research is needed to protect people’s health. In addition, modern education should provide the necessary knowledge to students, but also take care of the development of the critical thinking of future citizens, so that they can make the most appropriate decisions for their health.

Conformal Volumetric Grayscale Metamaterials.

Conformal artificial electromagnetic media that feature tailorable responses as a function of incidence wavelength and angle represent universal components for optical engineering. Conformal grayscale metamaterials are introduced as a new class of volumetric electromagnetic media capable of supporting highly multiplexed responses and arbitrary, curvilinear form factors. Subwavelength-scale voxels based on irregular shapes are designed to accommodate a continuum of dielectric values, enabling the freeform design process to reliably converge to exceptionally high figures of merit (FOMs) for a given multi-objective design problem. Through additive manufacturing of ceramic-polymer composites, microwave metamaterials, designed for the radio-frequency range of 8-12GHz, are experimentally fabricated and devices with extreme dispersion profiles, an airfoil-shaped beam-steering device, and a broadband, broad-angle conformal carpet cloak, are demonstrated. It is anticipated that conformal volumetric metamaterials will lead to new classes of compact and multifunctional imaging, sensing, and communications systems.

High-precision comparison of time scales over fiber optic lines using satellite modems with additional tone modulation

The use of a new type of modems with pseudonoise coding and additional tone modulation designed to compare reference time scales over telecommunication geostationary satellites is considered. Experimental studies were carried out on the possibility of comparing time scales of hydrogen keepers from the State primary standard of unit of time, frequency and national time scale using these modems via an optical link. A fiber-optical lines of various lengths were used for a two-way signal transmission. The output radio-frequency signals of the modems connected to the optical transmitters at the ends of the fiber-optical lines were transmitted towards each other on an optical carrier with a wavelength of 1.55 μm. Demodulation of optical signals into the radio frequency range was carried out using optical receivers at the ends of fiber lines. The results of experimental evaluation of type A uncertainty by comparing time scales using fiber-optical lines with 50, 100, and 200 km of length are presented. For the 200 km line, the type A measurement uncertainty does not exceed 3 ps for one day of averaging interval. For the first time, it has been experimentally shown that the implementation of the method of time scales comparison using modems with pseudo-noise coding and additional tone modulation over 200 km of fiber line is possible without the intermediate optical amplifiers. The result opens up the prospect of creating cascaded systems for comparing time scales of remote standards via fiber-optic communication lines with a smaller number of intermediate optical amplifiers.

Performance of the RF Detectors of the Astroneu Array

Since 2014, the university campus of Hellenic Open University (HOU) has hosted the Astroneu array, which is dedicated to the detection of extensive air showers (EAS) induced by high-energy cosmic rays (CR). The Astroneu array incorporates 9 large particle scintillation detectors and 6 antennas sensitive to the radio frequency (RF) range 1–200 MHz. The detectors are adjusted in three autonomous stations operating in an environment with a strong electromagnetic background. As shown by previous studies, EAS radio detection in such environments is possible using innovative noise rejection methods, as well as advanced analysis techniques. In this work, we present the analysis of the collected radio data corresponding to an operational period of approximately four years. We present the performance of the Astroneu radio array in reconstructing the EAS axis direction using different RF detector geometrical layouts and a technique for the estimation of the shower core by comparing simulation and experimental data. Moreover, we measure the relative amplitudes of the two mechanisms that give rise to RF emission (the Askaryan effect and geomagnetic emission) and show that they are in good agreement with previous studies as well as with the simulation predictions.

RT VIR – A SEMIREGULAR STAR WITH MASER EMISSION: MATHEMATICAL MODELLING OF OPTICAL VARIABILITY

The historical light curve of the semiregular pulsating star RT Vir (SRb, Sp M8III) with a ma-&#x0D; ser emission is analyzed based on the AAVSO database. The star is extensively studied in the IR, radio and the optical ranges. The value of the period from the CCVS (155 d ) conflicts with some observational data. Signs of a systematic variability were also detected in the radio frequency range with a period that was close to 200 days. Studies of the period showed that the period of this star varies with time and the latest value was found to be roughly 136 days. Period analysis result of the visual data from 1904 May to 2016 August provided by AAVSO for RT Vir. Published databases of "virtual observatories" - AAVSOnet, Hipparcos, ASAS-SN, KWS were used. Periodogram analysis revealed that the star still has several periods (320, 280, 169 and 153 days). In fact, the variations are not truly periodic, there are large shifts in time, changes in amplitude, and these smaller periods occur as smaller-amplitude peaks in-between the main ones with 320 period. Two-color diagrams of gloss in I and color index (V-I) from V were constructed. Approximation of “Running parabola” was carried out, average values &lt;V&gt;=8.457, &lt;I&gt;=3.658, &lt;B-V&gt;=+1.8 were determined.

Auroral kilometric radiation—The electron cyclotron maser paradigm

Auroral kilometric radiation (AKR) is the paradigm of intense radio emission from planetary magnetospheres. Being close to the electron gyro frequency and/or its lower harmonics, its observation indicates the non-thermal state of the source plasma. Emission is produced when the plasma enters a state of energetic excitation which results in deformation of the electron distribution function. Under certain conditions this leads to “quasi-coherent” emission. It is believed that the weakly-relativistic electron-cyclotron-maser instability is responsible for this kind of radiation. Since energetically radio radiation normally is not of primary importance in the large-scale magnetospheric phenomena, AKR as such has, for the purposes of large-scale magnetospheric physics, become considered a marginal problem. Here this notion is questioned. AKR while applying to the auroral region mainly during magnetospherically disturbed times carries just a fraction of the total substorm energy. It is, however, of diagnostic power in the physics of the upper auroral ionosphere and Space Weather research. As a fundamental physical problem of generation of radiation in non-thermal plasmas it remains not resolved yet. Many questions have been left open even when dealing only with the electron-cyclotron-maser. These can advantageously be studied in the magnetosphere proper both by observation and theory, the only continuously accessible place in space. The most important are listet here with hint on how they should be attacked. Its value is to be sought in the role it should play in application to the other magnetized planets, extra-solar planets, and to strongly magnetized astronomical objects as an important tool to diagnose the matter state responsible for radiation in the radio frequency range beyond thermal, shock or synchrotron radiation.

Аналіз теплового режиму електропровідного трубчастого елемента з тонким зовнішнім електропровідним покриттям за дії неусталеного електромагнітного поля

An electrically conductive tubular element with a thin external electri-cally conductive coating underthe action of an unsteady electromagnetic field of the radio frequency range is considered. To analyze the thermal re-gime, the initial-boundary problem of electrodynamics for a two-layer conductive non-ferromagnetic hollow cylinder under the action of an ex-ternal non-stationary electromagnetic field is formulated. The electromag-netic field is given by the values of the axial component of the magnetic field intensity vector on the inner and outer surfaces of the cylinder. To construct the general solution of the formulated initial-boundary value problem, a quadratic approximation of the key function (the axial compo-nent of the magnetic field intensity vector) along the radial coordinate in each constituent layer (base and cover) of the hollow cylinder was used. As a result, the original initial-boundary value problem for the key function is reduced to the Cauchy problem in terms of the time variable for the charac-teristics of the key function integral over the radial coordinate. The coeffi-cients of the approximation polynomials are presented through the integral characteristics of the key function and its given values on the inner and outer surfaces of the cylinder as a function of time. The solution of the Cauchy problem is obtained using the integral Laplacetransform. Expres-sions of the key function in each component layer of the cylinder are rec-orded in the form of quadratic polynomials, the coefficients of which are convolutions of functions describing the given limit values of the key func-tion on the inner and outer surfaces of the cylinder and homogeneous solu-tions of the Cauchy problem on integral characteristics. Expressions of the key function and Joule heat in the base and coating of the considered tubu-lar element under the action of an unsteady electromagnetic field in the mode with a pulsed modulating signal were obtained on the basis of gen-eral solutions for homogeneous non-stationary electromagnetic action. A computer analysis of the change in time and thickness of the constituent layers of this tubular element of the axial component of the vector of mag-netic field intensity and Joule heat was carried out.

A Power-Efficient CMOS Multi-Band Phased-Array Receiver Covering 24–71-GHz Utilizing Harmonic-Selection Technique With 36-dB Inter-Band Blocker Tolerance for 5G NR

This article introduces a power-efficient 24.25– 71-GHz multi-band phased-array receiver supporting all allocated fifth-generation mobile network new radio (5G NR) frequency range 2 (FR2) bands at 24/28/39/47 GHz and the potential 5G NR-U bands in unlicensed 57–71 GHz. A novel harmonic-selection technique is introduced to extend the operating bandwidth with low power consumption. By switching between the fundamental-selected mode, the second-harmonic-selected mode, and the third-harmonic-selected mode, only signals in the desired bands can be preserved, while the unselected mixing components are rejected. A dual-mode multi-band low-noise amplifier (LNA) based on a configurable transformer is adopted to realize broadband operation with minimized power consumption and noise figure (NF). The Hartley architecture is employed to further improve the image rejection performance. A hybrid-type polyphase filter (PPF) with a detector-based high-precision calibration block is utilized in this work to realize the Hartley operation with reduced insertion loss (IL). The proposed phased-array receiver is fabricated in a standard 65-nm bulk CMOS process. With the concerted efforts of all components, the proposed multi-band receiver can support 5G standard-compliant OFDMA-mode modulated signals up to 256QAM with a 400-MHz channel bandwidth from 24 to 71 GHz. Better than 36-dB inter-band blocker rejections can be maintained by this work. With existing of 0-dBc inter-band blockers at worst case frequencies, this receiver shows EVMs of −33.3, −30.9, −31.6, and −28.5 dB at 28, 39, 47.2, and 60.1 GHz, respectively. The power consumptions for a single receiver channel are 36, 32, 51, and 71 mW at 28, 39, 47.2, and 60.1 GHz, respectively.

Phase Noise Modeling and Experimental Demonstration of Single and Dual-Loop Direct Modulation Optoelectronic Oscillator

A single and dual loop direct modulation Opto-Electronic Oscillator (DMOEO) phase noise model for generation of low phase noise signal operating in Radio Frequency (RF) and microwave frequency range is proposed and experimentally demonstrated. The distribute feedback (DFB) laser diode is used in the proposed design to perform the RF to optical conversion by exploiting its non-linear transfer function characteristics, in contrast to external modulator in conventional OEO designs. We presented the theoretical phase noise model for single and multi-loop DMOEO deign with all possible noise contributions. Also, simulation scenarios have been demonstrated to show the impact of different noise source on the overall phase noise performance of the OEO. A single and dual loop DMOEO with phase noise of −112 dBc/Hz and −110 dBc/Hz at 10 kHz offset from 2.4 GHz carrier respectively is designed and the side mode suppression better than 50 dB is achieved for the generated signal with 11 dBm output power.