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Journal articles on the topic 'Active Radio Frequency Seekers'

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Author: Grafiati

Published: 6 September 2023

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1

Duan, Kai, Mohamad Orabi, Alexus Warchock, Zaynab Al-Akraa, Zeinab Ajami, Tae-Hwa Chun, and Joe F. Lo. "Monolithically 3D-Printed Microfluidics with Embedded µTesla Pump." Micromachines 14, no. 2 (January 17, 2023): 237. http://dx.doi.org/10.3390/mi14020237.

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Microfluidics has earned a reputation for providing numerous transformative but disconnected devices and techniques. Active research seeks to address this challenge by integrating microfluidic components, including embedded miniature pumps. However, a significant portion of existing microfluidic integration relies on the time-consuming manual fabrication that introduces device variations. We put forward a framework for solving this disconnect by combining new pumping mechanics and 3D printing to demonstrate several novel, integrated and wirelessly driven microfluidics. First, we characterized the simplicity and performance of printed microfluidics with a minimum feature size of 100 µm. Next, we integrated a microtesla (µTesla) pump to provide non-pulsatile flow with reduced shear stress on beta cells cultured on-chip. Lastly, the integration of radio frequency (RF) device and a hobby-grade brushless motor completed a self-enclosed platform that can be remotely controlled without wires. Our study shows how new physics and 3D printing approaches not only provide better integration but also enable novel cell-based studies to advance microfluidic research.

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2

Glasmachers, A. "Active miniature radio frequency field probe." Advances in Radio Science 1 (May 5, 2003): 161–64. http://dx.doi.org/10.5194/ars-1-161-2003.

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Abstract. For the measuring of the electromagnetic interference (e.g. on men) of RF fields produced by mobile communication equipment field probes are required with high spatial resolution and high sensitivity. Available passive probes show good results with respect to bandwidth and low field distortion, but do not provide the required sensitivity and dynamic range. A significant limitation for active miniature probes is the power supply problem, because batteries cannot be used. Therefore the effect of high impedance connection lines is examined by a numerical field simulation. Different approaches for the design of an active probe are discussed, a favourable solution with a logarithmic demodulator is implemented and measuring results are presented.

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3

Jones, Alex K., Swapna Dontharaju, Shenchih Tung, Peter J. Hawrylak, Leonid Mats, Raymond Hoare, James T. Cain, and Marlin H. Mickle. "Passive active radio frequency identification tags." International Journal of Radio Frequency Identification Technology and Applications 1, no. 1 (2006): 52. http://dx.doi.org/10.1504/ijrfita.2006.010711.

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4

Alnukari, A., P. Guillemet, Y. Scudeller, and S. Toutain. "Active Heatsink Antenna for Radio-Frequency Transmitter." IEEE Transactions on Advanced Packaging 33, no. 1 (February 2010): 139–46. http://dx.doi.org/10.1109/tadvp.2009.2023858.

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5

Mandal, Soumyajit, Serhii M. Zhak, and Rahul Sarpeshkar. "A Bio-Inspired Active Radio-Frequency Silicon Cochlea." IEEE Journal of Solid-State Circuits 44, no. 6 (June 2009): 1814–28. http://dx.doi.org/10.1109/jssc.2009.2020465.

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6

Saul, P. H. "Radio frequency to emitter coupled logic active detector." Electronics Letters 30, no. 14 (July 7, 1994): 1126–27. http://dx.doi.org/10.1049/el:19940749.

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7

D.Sangeetha and K.S.Gowthaman, T. Agalya, R. Mathumitha, P. Poongodi. "Active Mobile Phone Detector using Radio Frequency Signal." International Journal for Modern Trends in Science and Technology 6, no. 7 (July 31, 2020): 96–99. http://dx.doi.org/10.46501/ijmtst060715.

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8

Pan, Yong, Zi Ye Hou, Jiang Xiong, and Kai Hua Liu. "Research on the System of Radio Frequency Identification and Localization Works in Microwave." Applied Mechanics and Materials 441 (December 2013): 993–96. http://dx.doi.org/10.4028/www.scientific.net/amm.441.993.

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Radio frequency identification and localization is a key technology in the Internet of Things. This paper reports an ARM Cortex-M3 processor based hand-held radio frequency identification and localization terminal and a 8051 processor based active radio frequency tags. The terminal and the tags utilize STM32F103VET6 and the low power consumption STC12LE4052AD as their master controller, respectively. Both of them use Nordic nRF24L01 as their radio frequency identification module. The system works in 2.4GHz ISM microwave band and can read, write and locate radio frequency tags within 20m indoors. The actual measurement of active radio frequency tags shows that this terminal is highly stable and comparable in 2.4GHz microwave frequency radio identification and localization.

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9

Pan, Yong, Kai Hua Liu, Yi Gao, and Rui Zhao. "A Study on the System of Radio Frequency Identification and Localization Works in UHF." Advanced Materials Research 588-589 (November 2012): 932–35. http://dx.doi.org/10.4028/www.scientific.net/amr.588-589.932.

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This paper designs a hand-held radio frequency identification and localization terminal based on ARM Cortex-M3 processor and active radio frequency tags based on 8051 processor. This terminal uses STM32F103VET6 as its master controller, these tags use STC12C2052AD as their master controller. They all use Nordic nRF905 as their radio frequency identification module. The system works in 433M/868M/915MHz ISM UHF band and can read, write and locate radio frequency tags within 50m indoors. The actual measurement of active radio frequency tags shows that this terminal is highly stable and comparable in 433M/868M/915M ultra-high frequency radio identification and localization. The test results of this system are also analyzed and presented.

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10

Piccardo, Marco, Michele Tamagnone, Benedikt Schwarz, Paul Chevalier, Noah A. Rubin, Yongrui Wang, Christine A. Wang, et al. "Radio frequency transmitter based on a laser frequency comb." Proceedings of the National Academy of Sciences 116, no. 19 (April 24, 2019): 9181–85. http://dx.doi.org/10.1073/pnas.1903534116.

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Since the days of Hertz, radio transmitters have evolved from rudimentary circuits emitting around 50 MHz to modern ubiquitous Wi-Fi devices operating at gigahertz radio bands. As wireless data traffic continues to increase, there is a need for new communication technologies capable of high-frequency operation for high-speed data transfer. Here, we give a proof of concept of a compact radio frequency transmitter based on a semiconductor laser frequency comb. In this laser, the beating among the coherent modes oscillating inside the cavity generates a radio frequency current, which couples to the electrodes of the device. We show that redesigning the top contact of the laser allows one to exploit the internal oscillatory current to drive a dipole antenna, which radiates into free space. In addition, direct modulation of the laser current permits encoding a signal in the radiated radio frequency carrier. Working in the opposite direction, the antenna can receive an external radio frequency signal, couple it to the active region, and injection lock the laser. These results pave the way for applications and functionality in optical frequency combs, such as wireless radio communication and wireless synchronization to a reference source.

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11

Artyukh, V. S. "Physical Conditions in Active Galactic Nuclei." Symposium - International Astronomical Union 134 (1989): 535–36. http://dx.doi.org/10.1017/s0074180900141919.

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Self-absorption of synchrotron radiation in compact radio sources gives rise to a low-frequency cutoff in their spectra. To study this effect it is necessary to observe the radio sources at meter wavelengths with angular resolution < 1″. Such observations of compact radio sources located in active galactic nuclei lead to estimates of magnetic field strengths and relativistic electron number densities in the AGNs.

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12

Avdeev, Vladimir B., S. I. Babusenko, V. Yu Gorovoi, A. I. Katrusha, N. I. Kozachek, S. N. Panychev, D. V. Senkevich, and A. A. Chaplygin. "An Active Nonlinear Radio-Range Station with Frequency and Pulse Modulation for Measuring Distances to Radio-Frequency Sources." Telecommunications and Radio Engineering 65, no. 9 (2006): 847–56. http://dx.doi.org/10.1615/telecomradeng.v65.i9.80.

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13

Wu, Jie, Minghua Zhu, Bo Xiao, and Wei He. "Inertial measurement unit–aided dual-frequency radio frequency identification localization in line-of-sight and non-line-of-sight hybrid environment." International Journal of Distributed Sensor Networks 14, no. 3 (March 2018): 155014771876203. http://dx.doi.org/10.1177/1550147718762033.

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The mitigation of non-line-of-sight propagation conditions is one of main challenges in wireless signal–based indoor localization. When radio frequency identification localization technology is applied in applications, the received signal strength fluctuates frequently due to the shade and multipath effect of radio frequency signal, which could result in localization inaccuracy. In particular, when tag carriers are walking in line-of-sight and non-line-of-sight hybrid environment, great attenuation of received signal strength will happen, which would result in great positioning deviation. The article puts forward a dual-frequency radio frequency identification–based indoor localization approach in line-of-sight–non-line-of-sight hybrid environment with the help of inertial measurement unit. Dual-frequency radio frequency identification includes passive radio frequency identification and active radio frequency identification. Passive radio frequency identification is used to assist in determining the tag initial location with passive reader. Active radio frequency identification is used to locate the tag and send the sensor information to active radio frequency identification readers. The proposed method includes three improvements over previous received signal strength–based positioning methods: inertial measurement unit–aided received signal strength filtering, inertial measurement unit–aided line-of-sight/non-line-of-sight distinguishing, and inertial measurement unit–aided line-of-sight/non-line-of-sight environment switching. Also, Cramér–Rao low bound is calculated to prove theoretically that indoor positioning accuracy for the proposed method in line-of-sight and non-line-of-sight mixed environment is higher than position precision using only received signal strength information. Experiments are conducted to show that the proposed method can reduce the mean positioning error to around 3 m without site survey.

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14

Avinash, K., and P. H. Diamond. "Active control of edge localized modes by radio frequency waves." Physics of Plasmas 7, no. 11 (November 2000): 4616–21. http://dx.doi.org/10.1063/1.1290050.

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15

Tantawi, Sami G., Ronald D. Ruth, and A. E. Vlieks. "Active radio frequency pulse compression using switched resonant delay lines." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 370, no. 2-3 (February 1996): 297–302. http://dx.doi.org/10.1016/0168-9002(95)00816-0.

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16

Abdipour, Mahmoud, Gholamreza Moradi, and Reza Sarraf Shirazi. "Ultra-low noise active microstrip antenna." International Journal of Microwave and Wireless Technologies 6, no. 5 (December 17, 2013): 515–20. http://dx.doi.org/10.1017/s1759078713001074.

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An active receiving antenna for Radio Navigation and Radio Positioning applications in S-band frequency is designed and fabricated. In this active antenna, the amplifier is integrated with the radiator which is a rectangular patch antenna. This patch antenna is analyzed with full-wave momentum method. With the developed design routine, ultra-low noise active receiving antenna can be realized. The ADS software and its full-wave Momentum is used for simulation. The experimental results show good agreement with the simulation results.

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17

Mahony, Elizabeth K. "Unveiling the high-frequency radio source population with the AT20G survey." Proceedings of the International Astronomical Union 9, S304 (October 2013): 205–8. http://dx.doi.org/10.1017/s1743921314003780.

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AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

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18

Yin, Feifei, Zhongle Wu, Yitang Dai, Tianpeng Ren, Kun Xu, Jintong Lin, and Geshi Tang. "Stable fiber-optic time transfer by active radio frequency phase locking." Optics Letters 39, no. 10 (May 15, 2014): 3054. http://dx.doi.org/10.1364/ol.39.003054.

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19

Bartsch, Sebastian T., A. Rusu, and Adrian M. Ionescu. "A single active nanoelectromechanical tuning fork front-end radio-frequency receiver." Nanotechnology 23, no. 22 (May 10, 2012): 225501. http://dx.doi.org/10.1088/0957-4484/23/22/225501.

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20

Obeng, Yaw S., Chukwudi A. Okoro, Papa K. Amoah, Rhonda R. Franklin, and Pavel Kabos. "Low Frequency Radio Wave Detection of Electrically Active Defects in Dielectrics." ECS Journal of Solid State Science and Technology 5, no. 4 (November 3, 2015): P3025—P3030. http://dx.doi.org/10.1149/2.0051604jss.

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21

Doi, A., S. Kameno, K. Kohno, K. Nakanishi, and M. Inoue. "A high-frequency radio survey of low-luminosity active galactic nuclei." Monthly Notices of the Royal Astronomical Society 363, no. 2 (October 21, 2005): 692–704. http://dx.doi.org/10.1111/j.1365-2966.2005.09471.x.

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22

Falkovich, Igor S., Alexander A. Konovalenko, Anatoliy A. Gridin, Leonid G. Sodin, Igor N. Bubnov, Nikolay N. Kalinichenko, Sergey L. Rashkovskii, Dmitriy V. Mukha, and Peter L. Tokarsky. "Wide-band high linearity active dipole for low frequency radio astronomy." Experimental Astronomy 32, no. 2 (September 9, 2011): 127–45. http://dx.doi.org/10.1007/s10686-011-9256-z.

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23

Abraham, Zulema. "High frequency radio observations of the nucleus of Cen A." Symposium - International Astronomical Union 175 (1996): 25–26. http://dx.doi.org/10.1017/s0074180900079870.

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Cen A (NGC5128) is a giant radio galaxy that in several ways behaves like a weak active galactic nucleus. It presents three pairs of radio lobes and a compact core with a one sided jet (Jauncey et al. 1995). The compact core is highly variable in wavelengths ranging from the radio region to X and γ rays (Kinzer et al. 1995). In the radio domain, the emission from the core dominates at high frequencies and a considerable effort was made to study variability at 22 and 43 GHz for more than ten years (Botti & Abraham 1995).

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24

Kramer, Michael, and Kiriaki M. Xilouris. "Multi-frequency pulsar studies at high radio frequencies." International Astronomical Union Colloquium 160 (1996): 279–82. http://dx.doi.org/10.1017/s0252921100041701.

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AbstractWe report flux density measurements, polarimetric and timing observations of pulsars made at the highest radio frequencies to date, covering the widest frequency range from 1.4 GHz to 86 GHz. We find that the magnetic field maintains its dipolar structure throughout the active part of the magnetosphere, a region located close to the stellar surface and confined to a small slab of a few stellar radii. The change in width and shape of pulse profiles saturates at mm-wavelengths while the depolarization accelerates, leading to almost completely depolarized emission. Two pulsars seem to exhibit a turn-up in their flux density spectrum at mm-wavelengths.

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25

Slee, O. B., G. J. Nelson, J. L. Innis, R. T. Stewart, A. Vaughan, and A. E. Wright. "The Active Radio Star HD 36705." Publications of the Astronomical Society of Australia 6, no. 3 (1986): 312–16. http://dx.doi.org/10.1017/s132335800002693x.

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AbstractThe single G8V active chromosphere star HD36705 (AB Dor) was observed at 8.4 GHz with the Parkes 64 m telescope during three observing sessions involving a total of 21 days in the interval 1985 December to 1986 February. Subsequent photometric observations were made of the star with the 0.25 m and 0.45 m telescopes of the Monash Observatory in 1986 March-April. Two strong radio flares, each lasting three days, were detected; they yielded peak radio powers of P8.4≈4×109 W Hz-1, comparable with the microwave power emitted by the RS CVn binaries. Significant circular polarization of 13% left-hand was measured on only one of the six active days. The 8.4 GHz flux density showed smooth variation over an interval of several hours, consistent with the flare source being partly occulted by the stellar disk as the star rotated. When all the radio data was phase-binned using the known rotation period of 0.514 day we found two radio maxima corresponding to radio sources at stellar longitudes ~180° apart. The subsequent photometric data showed intensity variations that were consistent with the starspots at the same approximate longitudes. We thus interpret our radio curve as showing the presence of comparatively small (<0.5 D*) radio sources in the corona above the star spots. The upper limit to source diameter gives a peak brightness temperature ≥2×l010 K, which can be achieved by gyro-synchrotron emission only if the source is optically thick and the electrons, with average energy ~ 2 MeV, have a hard energy spectrum. The observed radiation can be due only to very high harmonics of the gyro-frequency, leading to an estimate for the magnetic field strength of ~30G.

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26

Stanislavsky, A. A., I. N. Bubnov, A. A. Konovalenko, A. A. Gridin, V. V. Shevchenko, L. A. Stanislavsky, D. V. Mukha, and A. A. Koval. "First Radio Astronomy Examination of the Low-Frequency Broadband Active Antenna Subarray." Advances in Astronomy 2014 (2014): 1–5. http://dx.doi.org/10.1155/2014/517058.

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We present the 25-element active antenna array and its remote control in the framework of the GURT project, the Ukrainian Radio Telescope of a new age. To implement beamforming, the array is phased with the help of discrete cable delay lines in analog manner. The remote control of the array is carried out through the paired encoder and decoder that can transmit parallel data about antenna codes serially. The microcontroller provides the online interaction between personal computer and beamformers with the help of the encoder-decoder system through wires or wireless. The antenna pattern has been measured by radio astronomy methods.

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27

Pardo, Juan R., Pierre J. Encrenaz, and Daniel Breton. "Utilization of the Radiofrequency Spectrum above 1 GHz by Passive Services." Symposium - International Astronomical Union 196 (2001): 255–63. http://dx.doi.org/10.1017/s0074180900164174.

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Microwave atmospheric radiometry and radio, mm and sub-mm astronomy are “passive” services, i.e. not involved in any man-made transmission but only concerned with the reception of naturally occurring radio waves. The intensity of the radiation received is not subject to human control, unlike the situation for active services. All active services operate in bands occupied by natural signals of atmospheric and cosmic origin and the active service tranmissions may be powerful enough to noticeably interfere with reception of those signals by scientific services. A conflict exists for the coexistence of active and passive services in many frequency bands, which leads to a need for regulating how to share the electromagnetic spectrum. This document gives an overview of the problems of frequency sharing in the longwave region of the electromagnetic spectrum (radio to submillimetre waves).

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28

Stanislavsky, Aleksander A., Igor N. Bubnov, Artem A. Koval, and Serge N. Yerin. "Parker Solar Probe detects solar radio bursts related with a behind–the–limb active region." Astronomy & Astrophysics 657 (December 21, 2021): A21. http://dx.doi.org/10.1051/0004-6361/202141984.

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Context. The interpretation of solar radio bursts observed by Parker Solar Probe (PSP) in the encounter phase plays a key role in understanding intrinsic properties of the emission mechanism in the solar corona. Lower time–frequency resolution of the PSP receiver can be overcome by simultaneous ground–based observations using more advanced antennas and receivers. Aims. In this paper we present such observations for which the active active region 12 765, begetter of type III, J, and U solar bursts, was within sight of ground–based instruments and behind the solar limb of the PSP spacecraft. Methods. We used a subarray of the Giant Ukrainian Radio Telescope to get the spectral properties of radio bursts at the frequency range of 8–80 MHz, as well as the PSP radio instruments with a bandwidth of 10.5 kHz–19.2 MHz, during solar observations on June 5, 2020. Results. We directly detected the radio events initiated by the active region behind the solar limb of the PSP spacecraft, using special conditions in the solar corona, due to the absence of active regions from the PSP side. Following the generation mechanism of solar radio emission, we refined the density model for the solar corona above the active region 12765 responsible for the radio bursts. Based on the PSP spacecraft position near the Sun and delays of radio waves between space– and ground–based records, we found the corresponding radio responses on the PSP spectrogram. Conclusions. The absence of sunspots from the PSP side contributes to the propagation of radio waves from a dense loop of the Sun to quiet regions with low densities, through which PSP instruments can detect the radiation.

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29

Lang, Kenneth R. "Flare stars at radio wavelengths." Symposium - International Astronomical Union 137 (1990): 125–38. http://dx.doi.org/10.1017/s0074180900187595.

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The radio emission from dMe flare stars is discussed using Very Large Array and Arecibo observations as examples. Active flare stars emit weak, unpolarized, quiescent radio radiation that may be always present. Although thermal bremsstrahlung and/or thermal gyroresonance radiation account for the slowly-varying, quiescent radio radiation of solar active regions, these processes cannot account for the long-wavelength quiescent radiation observed from nearby dMe flare stars. It has been attributed to nonthermal gyrosynchrotron radiation, but some as yet unexplained mechanism must be continually producing the energetic electrons. Long-duration (hours), narrow-band (Δv/v < 0.1) radiation is also emitted from some nearby dMe stars at 20 cm wavelength. Such radiation may be attributed to coherent plasma radiation or to coherent electron-cyclotron masers. Impulsive stellar flares exhibit rapid variations (< 100 msec) that require radio sources that are smaller than the star in size, and high brightness temperatures TB > 1015 K that are also explained by coherent radiation processes. Quasi-periodic temporal fluctuations suggest pulsations during some radio flares. Evidence for frequency structure and positive or negative frequency drifts during radio flares from dMe stars is also presented.

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30

Wang, Congsi, Haihua Li, Kang Ying, Qian Xu, Na Wang, Baoyan Duan, Wei Gao, Lan Xiao, and Yuhu Duan. "Active Surface Compensation for Large Radio Telescope Antennas." International Journal of Antennas and Propagation 2018 (2018): 1–17. http://dx.doi.org/10.1155/2018/3903412.

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With the development of radio telescope antennas with large apertures, high gain, and wide frequency bands, compensation methods, such as mechanical or electronic compensation, are obviously essential to ensure the electrical performance of antennas that work in complex environments. Since traditional compensation methods can only adjust antenna pointing but not the surface accuracy, which are limited for obtaining high surface precision and aperture efficiency, active surface adjustment has become an indispensable tool in this field. Therefore, the development process of electrical performance compensation methods for radio telescope antennas is introduced. Further, a series of analyses of the five key technologies of active surface adjustment is presented. Then, four typical large antennas that have been designed with active main reflector technology are presented and compared. Finally, future research directions and suggestions for reflector antenna compensation methods based on active surface adjustment are presented.

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31

Keikha, Mahsa, Jalal Taheri Kahnamouei, and Mehrdad Moallem. "Radio Frequency Cavity’s Analytical Model and Control Design." Vibration 6, no. 2 (March 25, 2023): 319–42. http://dx.doi.org/10.3390/vibration6020020.

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Reduction or suppression of microphonic interference in radio frequency (RF) cavities, such as those used in Electron Linear Accelerators, is necessary to precisely control accelerating fields. In this paper, we investigate modeling the cavity as a cylindrical shell and present its free vibration analysis along with an appropriate control scheme to suppress vibrations. To this end, we first obtain an analytical mechanical dynamic model of a nine-cell cavity using a modified Fourier-Ritz method that provides a unified solution for cylindrical shell systems with general boundary conditions. The model is then verified using the ANSYS software in terms of a comparison of eigenfrequencies which prove to be identical to the proposed model. We also present an active observer-based vibration control scheme to suppress the dominant mechanical modes of the cavity. The control system performance is investigated using simulations.

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32

Bubnov, I. N., O. O. Konovalenko, P. L. Tokarsky, O. M. Korolev, S. M. Yerin, and L. O. Stanislavsky. "CREATION AND APPROBATION OF A LOW-FREQUENCY RADIO ASTRONOMY ANTENNA FOR STUDIES OF OBJECTS OF THE UNIVERSE FROM THE MOON'S FARSIDE." Radio physics and radio astronomy 26, no. 3 (September 14, 2021): 197–210. http://dx.doi.org/10.15407/rpra26.03.197.

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Purpose: Theoretical and experimental studies of the active antenna – an element of the low-frequency radio telescope antenna array for the future observatory on the farside of the Moon. Design/methodology/approach: To study the active antenna, consisting of a complex-shaped dipole and a low-noise amplifier, we used its mathematical model in the form of a two-port network, whose electrical parameters are set by the scattering matrix, the noise parameters being set by the covariance matrix of the spectral densities of noise waves. This model allows ma[1]king the correct analysis of the signal-to-noise ratio at the active antenna output with account for the external and internal noise sources. The modelling results were compared with those of experimental measurements of antenna characteristics. A series of radio astronomy observations were made with the developed antenna under the Earth environmental conditions. Findings: A numerical analysis of the radio telescope active antenna parameters has been made in a wide frequency range of 4–40 MHz. Two versions of the low-noise amplifier were developed to operate in the active antenna under the space and Earth environmental conditions. Under the Earth conditions, it has been experimentally proven that the range of problems, which such radio telescopes can effectively solve at low frequencies, is quite wide – from the solar research to the search for cosmological effects. Conclusions: The results of numerical simulations and experimental measurements obtained in this work have shown a satisfactory agreement between them for the most of the frequency range. The results of this work can be useful in the research and development of active antennas designed for operation at the decameter and hectometer wavelength ranges, particularly those intended for using under the space environmental conditions. Keywords: active antenna, Moon, radio astronomy observations, sensitivity

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33

Kovalev, Y. Y. "Strong Radio Outbursts in Six Active Galactic Nuclei in 1997-1998." Symposium - International Astronomical Union 194 (1999): 418–19. http://dx.doi.org/10.1017/s0074180900162436.

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The beginnings of strong radio flares in six AGNs were detected and their evolution was studied using 1–22 GHz five epoch instantaneous spectral observations in 1997–1998. The phenomena started at the highest frequency and moved to the lower frequency in a regular fashion. Such behavior of the flares in AGNs can be explained by synchrotron emission from a compact relativistic jet implying different physical models which are discussed. For different types of AGNs the same behavior of flares is revealed, in favor of the same basic physical model for BL Lacs and quasars. A birth of new VLBI components in compact jets associated with these outbursts is predicted.

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34

Rajpurohit, K., R. J. van Weeren, M. Hoeft, F. Vazza, M. Brienza, W. Forman, D. Wittor, et al. "Deep Low-frequency Radio Observations of A2256. I. The Filamentary Radio Relic." Astrophysical Journal 927, no. 1 (March 1, 2022): 80. http://dx.doi.org/10.3847/1538-4357/ac4708.

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Abstract We present deep and high-fidelity images of the merging galaxy cluster A2256 at low frequencies using the upgraded Giant Metrewave Radio Telescope (uGMRT) and LOw-Frequency ARray (LOFAR). This cluster hosts one of the most prominent known relics with a remarkably spectacular network of filamentary substructures. The new uGMRT (300–850 MHz) and LOFAR (120–169 MHz) observations, combined with the archival Karl G. Jansky Very Large Array (VLA; 1–4 GHz) data, allowed us to carry out the first spatially resolved spectral analysis of the exceptional relic emission down to 6″ resolution over a broad range of frequencies. Our new sensitive radio images confirm the presence of complex filaments of magnetized relativistic plasma also at low frequencies. We find that the integrated spectrum of the relic is consistent with a single power law, without any sign of spectral steepening, at least below 3 GHz. Unlike previous claims, the relic shows an integrated spectral index of −1.07 ± 0.02 between 144 MHz and 3 GHz, which is consistent with the (quasi)stationary shock approximation. The spatially resolved spectral analysis suggests that the relic surface very likely traces the complex shock front, with a broad distribution of Mach numbers propagating through a turbulent and dynamically active intracluster medium. Our results show that the northern part of the relic is seen edge-on and the southern part close to face-on. We suggest that the complex filaments are regions where higher Mach numbers dominate the (re)acceleration of electrons that are responsible for the observed radio emission.

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Schubert, M., L. Kilzer, T. Dubielzig, M. Schilling, C. Ospelkaus, and B. Hampel. "Active impedance matching of a cryogenic radio frequency resonator for ion traps." Review of Scientific Instruments 93, no. 9 (September 1, 2022): 093201. http://dx.doi.org/10.1063/5.0097583.

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A combination of direct current (DC) fields and high amplitude radio frequency (RF) fields is necessary to trap ions in a Paul trap. Such high electric RF fields are usually reached with the help of a resonator in close proximity to the ion trap. Ion trap based quantum computers profit from good vacuum conditions and low heating rates that cryogenic environments provide. However, an impedance matching network between the resonator and its RF source is necessary, as an unmatched resonator would require higher input power due to power reflection. The reflected power would not contribute to the RF trapping potential, and the losses in the cable induce additional heat into the system. The electrical properties of the matching network components change during cooling, and a cryogenic setup usually prohibits physical access to integrated components while the experiment is running. This circumstance leads to either several cooling cycles to improve the matching at cryogenic temperatures or the operation of poorly matched resonators. In this work, we demonstrate an RF resonator that is actively matched to the wave impedance of coaxial cables and the signal source. The active part of the matching circuit consists of a varactor diode array. Its capacitance depends on the DC voltage applied from outside the cryostat. We present measurements of the power reflection, the Q-factor, and higher harmonic signals resulting from the nonlinearity of the varactor diodes. The RF resonator is tested in a cryostat at room temperature and cryogenic temperatures, down to 4.3 K. A superior impedance matching for different ion traps can be achieved with this type of resonator.

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Porter, J. David, Richard E. Billo, and Marlin H. Mickle. "Effect of active interference on the performance of radio frequency identification systems." International Journal of Radio Frequency Identification Technology and Applications 1, no. 1 (2006): 4. http://dx.doi.org/10.1504/ijrfita.2006.010699.

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Zhou, Junyi, and Jing Shi. "Performance evaluation of object localization based on active radio frequency identification technology." Computers in Industry 60, no. 9 (December 2009): 669–76. http://dx.doi.org/10.1016/j.compind.2009.05.002.

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Piepmeier, Jeffrey R., Joel T. Johnson, Priscilla N. Mohammed, Damon Bradley, Christopher Ruf, Mustafa Aksoy, Rafael Garcia, Derek Hudson, Lynn Miles, and Mark Wong. "Radio-Frequency Interference Mitigation for the Soil Moisture Active Passive Microwave Radiometer." IEEE Transactions on Geoscience and Remote Sensing 52, no. 1 (January 2014): 761–75. http://dx.doi.org/10.1109/tgrs.2013.2281266.

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39

Kallunki, J., V. Bezrukovs, W. Madkour, and P. Kirves. "Importance of Spectrum Management in Radio Astronomy." Latvian Journal of Physics and Technical Sciences 59, s3 (June 1, 2022): 30–38. http://dx.doi.org/10.2478/lpts-2022-0022.

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Abstract The increasing terrestrial and space-borne communications are causing major problems to the radio astronomy observations. Only a minor part of the frequencies is allocated to the passive services, such as Radio Astronomy Services (RAS). There are only a few, relatively narrow frequency bands below 20 GHz, which are still suitable for the radio astronomical observations. In addition, Out-of-Band (OoB) emissions will be a real threat to the observations on these bands. On behalf of all European radio astronomers, the Committee on Radio Astronomy Frequencies (CRAF) of the European Science Foundation (ESF) coordinates activities to keep the frequency bands used by radio astronomy and space sciences free of interference. Along with interference caused by active radio communication services, the local electronic device selection should be considered in the observatories. For instance, more common LED based lamps could cause harmful interference for the observations. Thus, it is very important to perform continuous radio frequency interference (RFI) monitoring locally, in each radio observatory.

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Reece, Charles E., and Gianluigi Ciovati. "Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications." Reviews of Accelerator Science and Technology 05 (January 2012): 285–312. http://dx.doi.org/10.1142/s1793626812300113.

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Superconducting rf (SRF) technology is evolving rapidly, as are its applications. While there is active exploitation of what one may call the current state-of-the-practice, there is also rapid progress in expanding in several dimensions the accessible and useful parameter space. While state-of-the-art performance sometimes outpaces thorough understanding, the improving scientific understanding from active SRF research is clarifying routes to obtain optimum performance from present materials and opening avenues beyond the standard bulk niobium. The improving technical basis understanding is enabling process engineering to improve both performance confidence and reliability and also unit implementation costs. Increasing confidence in the technology enables the engineering of new creative application designs. We attempt to survey this landscape to highlight the potential for future accelerator applications.

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Shen, Jianguo, Guiling Wu, Liang Hu, Weiwen Zou, and Jianping Chen. "Active phase drift cancellation for optic-fiber frequency transfer using a photonic radio-frequency phase shifter." Optics Letters 39, no. 8 (April 9, 2014): 2346. http://dx.doi.org/10.1364/ol.39.002346.

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Mahony, Elizabeth, Ron Ekers, Marcella Massardi, Tara Murphy, and Elaine Sadler. "The Australia Telescope 20 GHz (AT20G) Survey." Proceedings of the International Astronomical Union 5, S267 (August 2009): 264. http://dx.doi.org/10.1017/s1743921310006411.

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The recently completed AT20G survey provides the largest and most complete sample of high-frequency selected radio sources yet obtained, and offers new insights into the nature of the high-frequency active galaxy population. Here we focus on the optical properties of this survey which highlights the difference of the AT20G source population compared to other radio-selected AGN samples.

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Martí-Vidal, Iván, and Ciriaco Goddi. "High-Frequency Polarization Variability from Active Galactic Nuclei." Galaxies 9, no. 3 (July 15, 2021): 51. http://dx.doi.org/10.3390/galaxies9030051.

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The linear polarization of non-thermal emission encodes information about the structure of the magnetic fields, either from the region where the emission is produced (i.e., the intrinsic polarization angle) and/or from the screens of magnetized plasma that may be located on its way towards Earth (i.e., the effect of Faraday rotation). In addition, the variability timescale of the polarized emission, or its Faraday rotation, can be used to estimate the size of the region where the emission (or the Faraday rotation) originates. The observation of polarized emission from active galactic nuclei (AGN) and, in particular, its time evolution, also provides information about the critical role that magnetic fields may play in the process of jet launching and propagation. In this paper, we review some recent results about polarization variability from the cores of AGN jets, including observations at high spatial resolutions and/or at high radio frequencies.

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Gurov, E. V., S. U. Uvaysov, V. V. Chernoverskaya, and R. M. Uvaysov. "Very high frequency radio receiver preselector design." Russian Technological Journal 9, no. 6 (December 2, 2021): 37–45. http://dx.doi.org/10.32362/2500-316x-2021-9-6-37-45.

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Objectives. The quality of a radio receiver preselector largely determines its main characteristics, including sensitivity. A preselector usually consists of linear elements: inductors, capacitors, low noise amplifiers, and switches. At high frequencies, the components cannot be considered as ideal ones, since active and reactive parasitic parameters significantly affect the frequency response of the components and, as a consequence, the network. Therefore, simulation of the networks requires more sophisticated component models, which take into account parasitic parameters. However, if refined components models are applied, it is still possible to obtain unsatisfactory results, since interconnections and footprints pads also affect the frequency response. This is true even if short lines with a length of about 5 mm are used at frequencies of about 100 MHz. These features must be taken into account for RF network design. The purpose of the work is to ensure the required characteristics of the preselector in the design process based on computer simulation.Methods. Egor Gurov’s methodology for analog VHF LC-filters was applied to radio receiver preselector design. The methodology contains the methods of discrete optimization, Monte-Carlo method, momentum analysis with Green’s functions. Experimental results were obtained by prototype implementation and measurement with a vector network analyzer. The purpose of the work is to ensure the required preselector characteristics in the design process based on computer simulation.Results. The article presents the preselector design process. The preselector contains two analog switches, an analog band-pass filter, an analog high-pass filter, and a low-noise amplifier. Simulation and experimental results with their comparison are presented in the article.Conclusions. Satisfactory results were obtained. It means that Egor Gurov’s method can be applied for more complex networks design such as radio receiver preselectors.

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Osadchuk, O. V., V. S. Osadchuk, I. O. Osadchuk, A. O. Semenov, V. V. Martyniuk, and M. O. Prytula. "Investigation of a radio-frequency temperature transducer with a thermosensitive resistive element based on a complex compound of heterometallic β-diketonate." IOP Conference Series: Materials Science and Engineering 1254, no. 1 (September 1, 2022): 012027. http://dx.doi.org/10.1088/1757-899x/1254/1/012027.

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Abstract The article considers a new electrical circuit of a microelectronicradio-frequency measuring temperature transducer with a thermosensitive resistive element based on a complex compound of heterometallicβ-diketonate.The main characteristics of the researched radio-frequency temperature transducer with a thermosensitive resistive element based on a complex compound of heterometallic β-diketonate are obtained: the dependences of the active and reactive components of the full impedance of the radio-frequency measuring temperature transducer, the conversion function and the sensitivity equation.

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Chen, Yongyun, Qiusheng Gu, Junhui Fan, Xiaoling Yu, Nan Ding, Dingrong Xiong, and Xiaotong Guo. "Curvature of the Spectral Energy Distribution, Compton Dominance, and Synchrotron Peak Frequency in Jetted Active Galactic Nuclei." Astrophysical Journal 944, no. 2 (February 1, 2023): 157. http://dx.doi.org/10.3847/1538-4357/acb4e8.

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Abstract We collect a large sample with a reliable redshift detected by the Fermi satellite after 10 yr of data (4FGL-DR2), including blazars, gamma-ray narrow-line Seyfert 1 galaxies (γNLS1s), and radio galaxies. The spectral energy distributions of these Fermi sources are fitted by using a second-degree polynomial, and some important parameters including spectral curvature, synchrotron peak frequency, and peak luminosity are obtained. Based on those parameters, we discuss the Fermi blazar sequence and the particle acceleration mechanism. Our main results are as follows: (i) By studying the relationship between the synchrotron peak frequency and the synchrotron peak frequency luminosity, jet kinetic power, and gamma-ray luminosity for jetted active galactic nuclei (AGNs), we find an “L” shape in the Fermi blazar sequence. (ii) There is a significant anticorrelation between the Compton dominance, the black hole spin, and the synchrotron peak frequency for jetted AGNs, respectively. These results support that the γNLS1s and radio galaxies belong to the Fermi blazar sequence. (iii) On the basis of previous work, statistical or stochastic acceleration mechanisms can be used to explain the relationship between the synchrotron peak frequency and synchrotron curvature. For different subclasses, the correlation slopes are different, which implies that the Fermi sources of different subclasses have different acceleration mechanisms. (iv) Flat-spectrum radio quasars and γNLS1s have a higher median spin of a black hole than BL Lac objects and radio galaxies.

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Shabala, Stanislav S., Nika Jurlin, Raffaella Morganti, Marisa Brienza, Martin J. Hardcastle, Leith E. H. Godfrey, Martin G. H. Krause, and Ross J. Turner. "The duty cycle of radio galaxies revealed by LOFAR: remnant and restarted radio source populations in the Lockman Hole." Monthly Notices of the Royal Astronomical Society 496, no. 2 (April 30, 2020): 1706–17. http://dx.doi.org/10.1093/mnras/staa1172.

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ABSTRACT Feedback from radio jets associated with active galactic nuclei (AGNs) plays a profound role in the evolution of galaxies. Kinetic power of these radio jets appears to show temporal variation, but the mechanism(s) responsible for this process are not yet clear. Recently, the LOw Frequency ARray (LOFAR) has uncovered large populations of active, remnant, and restarted radio jet populations. By focusing on LOFAR data in the Lockman Hole, in this work we use the Radio AGNs in Semi-Analytic Environments (RAiSE) dynamical model to present the first self-consistent modelling analysis of active, remnant, and restarted radio source populations. Consistent with other recent work, our models predict that remnant radio lobes fade quickly. Any high (>10 per cent) observed fraction of remnant and restarted sources therefore requires a dominant population of short-lived jets. We speculate that this could plausibly be provided by feedback-regulated accretion.

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Vaughan, A. E., and M. I. Large. "A Search for 843 MHz Radio Emission from Active Stars." Publications of the Astronomical Society of Australia 6, no. 3 (1986): 319–22. http://dx.doi.org/10.1017/s1323358000026953.

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AbstractKnown Southern flare stars and RSCVn-like variables are being observed with the Molonglo Observatory Synthesis Telescope in an attempt to detect quiescent (non-flaring) emission. Two flare stars out of 7 and one RSCVn out of 8 have been detected. Quiescent emission has not been observed previously from these sources at such a low frequency. All sources so far detected have mean flux densities below 10 mJy and in at least two of them the emission varies with a time scale of about one day.

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Paramonov, A. A., and Van Zung Hoang. "Joint use of frequency-time division and antinoise coding in radio communication systems with FHSS." Russian Technological Journal 9, no. 4 (August 26, 2021): 77–84. http://dx.doi.org/10.32362/2500-316x-2021-9-4-77-84.

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In the context of continuous improvement of radio prospecting and active radio jamming technics along with introduction of automated active countermeasures systems (ACS), the frequency-hopping spread spectrum (FHSS) radio communication systems (RCS) are widely used in order to improve reliability and noise immunity of data transmission. The noise immunity of the RCS affected by unintentional or deliberate interference can be significantly perfected by the combined use of frequency-time division and antinoise coding. This paper explores the case when the interference created by an ACS system with a limited transmitter power covers a part of the RCS frequency range. The receiver gets input mix of the wanted signal, the receiver noise, and probably a deliberate interference also considered as a noise. The article analyzes the noise immunity of signals reception with FHSS in the low-speed radio systems with joint use of frequency-time division of information subsymbols and noise combating codes when the deliberate interference destructively impacts a part of the RCS working band. Dependence of the bit error probability on the signal-to-noise ratio is calculated for the joint use of frequency division of information subsymbols and noise combating codes. It is shown that due to effective use of the frequency-energy resource of a radio line, considering the use of correction codes, a quite high noise immunity of RCS under the influence of deliberate interference can be assured. The indicated dependences of the error probability on the signal-to-noise ratio confirm that the reliability of data transmission can be significantly increased by the proper combination of signal spectrum spreading, applying of correction codes, and frequency division of subsymbols followed by their weight processing.

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Li, Chien-Hao, Jen-Chieh Hu, Syang-Yun Tzeng, Chu-Ya Hsiao, Yen-Chung Lin, and Wei-Da Guo. "23‐2: Operation Method of Changing Data Rate for High‐Speed Signal Transmission on Display System." SID Symposium Digest of Technical Papers 54, no. 1 (June 2023): 306–9. http://dx.doi.org/10.1002/sdtp.16553.

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This study proposed a driving method for switching the operating frequency of a source driver based on single frame. The main purpose of this approach is to allow each frame to operate at different frequencies, avoiding energy accumulation that leads to problems of WWAN‐related radio frequency interference. Since the frequency is changed based on the unit of one frame, data transmission is performed at the same frequency in the active area of display, which expands the adjustment range of operating frequency without increasing the total jitter (Tj) of the transmitted signal. In addition to effectively reducing radio frequency interference, it also avoids the shortcomings of traditional spread spectrum.

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