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Articoli di riviste sul tema "Radio frequency"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 marzo 2025

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1

NECHIBVUTE, Action, Albert CHAWANDA, Nicholas TARUVINGA e Pearson LUHANGA. "Radio Frequency Energy Harvesting Sources". Acta Electrotechnica et Informatica 17, n. 4 (1 dicembre 2017): 19–27. http://dx.doi.org/10.15546/aeei-2017-0030.

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2

Jayati, Ari Endang, Wahyu Minarti e Sri Heranurweni. "Analisa Teknis Penetapan Kanal Frekuensi Radio Untuk Lembaga Penyiaran Radio Komunitas Wilayah Kabupaten Batang". Jurnal ELTIKOM 5, n. 2 (10 settembre 2021): 73–80. http://dx.doi.org/10.31961/eltikom.v5i2.361.

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The radio frequency spectrum constitutes a limited and strategic natural resource with high economic value, so it must be managed effectively and efficiently to obtain optimal benefits by observing national and international legal principles. Radio Community Broadcasting Institution uses limited frequency allocation in three channels, namely, in the frequency channels 202 (107.7 MHz), 203 (107.8 MHz), and 204 (107.9 MHz), with limited transmit power and area coverage. The problem in this research is the frequency overlap with other community radios in an area. The issue raised is whether it is possible to establish a new community radio in the Batang Regency area by paying attention to existing radios that have licenses in districts/cities that are in the area directly adjacent to Batang Regency by considering the limited allocation of radio frequency channels community, without the occurrence of radio frequency interference with other community radios. The purpose of this research is to solve these problems. It is necessary to have a policy in determining radio frequency users to get good quality radio broadcast reception. The method used is to analyze the frequency determination technique based on the interference analysis on other community broadcasters. By using the Radio Mobile Software for frequency repetition simulation, in this research, the results show that Batang FM Community Radio does not allow to get frequency channels for community radio operations. After all, it interferes with the Service Area of Soneta FM Radio in Pekalongan City because it does not meet the requirements for determining the frequency channel = Eu> NF, namely the Nuisance Field (NF) value of 109.7 dB is greater than the Minimum Usable Field strength (Eu) of 66 dB. In comparison, Limpung FM Radio gets radio frequency on channel 203 (frequency 107.8 MHz) because it meets the requirements for determining the frequency channel = Eu> NF, namely the Minimum Usable Field strength (Eu) 66 dB greater than the Nuisance Field (NF) of 55.7 dB.

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3

Sackenheim, Maureen McDaniel. "Radio Frequency Ablation". Journal of Diagnostic Medical Sonography 19, n. 2 (marzo 2003): 88–92. http://dx.doi.org/10.1177/8756479303251097.

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4

Dondelinger, Robert M. "Radio Frequency Identification". Biomedical Instrumentation & Technology 44, n. 1 (1 gennaio 2010): 44–47. http://dx.doi.org/10.2345/0899-8205-44.1.44.

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5

Wyld, David C. "Radio Frequency Identification". Cornell Hospitality Quarterly 49, n. 2 (maggio 2008): 134–44. http://dx.doi.org/10.1177/1938965508316147.

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6

Scheck, Anne. "Radio Frequency Identification". Emergency Medicine News 28, n. 3 (marzo 2006): 34–35. http://dx.doi.org/10.1097/01.eem.0000292061.54727.06.

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7

Ekers, R. D., e J. F. Bell. "Radio Frequency Interference". Symposium - International Astronomical Union 199 (2002): 498–505. http://dx.doi.org/10.1017/s0074180900169669.

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We describe the nature of the interference challenges facing radio astronomy in the next decade. These challenges will not be solved by regulation only, negotiation and mitigation will become vital. There is no silver bullet for mitigating against interference. A successful mitigation approach is most likely to be a hierarchical or progressive approach throughout the telescope and signal conditioning and processing systems. We summarise some of the approaches, including adaptive systems.

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8

Westra, Bonnie L. "Radio Frequency Identification". AJN, American Journal of Nursing 109, n. 3 (marzo 2009): 34–36. http://dx.doi.org/10.1097/01.naj.0000346925.67498.a4.

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9

Rajaraman, V. "Radio frequency identification". Resonance 22, n. 6 (giugno 2017): 549–75. http://dx.doi.org/10.1007/s12045-017-0498-6.

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10

., Manishkumar R. Solanki. "RADIO FREQUENCY IDENTIFICATION". International Journal of Research in Engineering and Technology 06, n. 01 (25 gennaio 2017): 129–33. http://dx.doi.org/10.15623/ijret.2017.0601024.

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11

Rao, Raghavendra. "RADIO FREQUENCY IDENTIFICATION". International Journal of Innovative Research in Advanced Engineering 09, n. 12 (31 dicembre 2022): 489–92. http://dx.doi.org/10.26562/ijirae.2022.v0912.05.

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Radio-frequency identification (RFID) is a technology that uses communication via electromagnetic waves to exchange data between a terminal and an electronic tag attached to an object, for the purpose of identification and tracking. Some tags can be read from several meters away and beyond the line of sight of the reader. Radio-frequency identification involves interrogators (also known as readers), and tags (also known as labels). Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, and other specialized functions.

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12

Ayun, Moshe Ben, Arye Schwarzbaum, Seva Rosenberg, Monika Pinchas e Shmuel Sternklar. "Photonic radio frequency phase-shift amplification by radio frequency interferometry". Optics Letters 40, n. 21 (19 ottobre 2015): 4863. http://dx.doi.org/10.1364/ol.40.004863.

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13

Mericli, Benjamin S., Ajay Ogirala, Peter J. Hawrylak e Marlin H. Mickle. "A Passive Radio Frequency Amplifier for Radio Frequency Identification Tags". Journal of Low Power Electronics 7, n. 3 (1 agosto 2011): 453–58. http://dx.doi.org/10.1166/jolpe.2011.1139.

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14

Li, Wei, Mingjian Ju, Qinghui Li, Ruixin Li, Wenxiu Yao, Yimiao Wu, Yajun Wang, Long Tian, Shaoping Shi e Yaohui Zheng. "Squeezing-enhanced resolution of radio-frequency signals". Chinese Optics Letters 22, n. 7 (2024): 072701. http://dx.doi.org/10.3788/col202422.072701.

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15

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, n. 19 (24 aprile 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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16

Dallacasa, Daniele. "High Frequency Peakers". Publications of the Astronomical Society of Australia 20, n. 1 (2003): 79–84. http://dx.doi.org/10.1071/as03005.

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AbstractThere is quite a clear anticorrelation between the intrinsic peak frequency and the overall radio source size in compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) radio sources. This feature is interpreted in terms of synchrotron self-absorption (although free–free absorption may play a role as well) of the radiation emitted by a small radio source which is growing within the inner region of the host galaxy. This leads to the hypothesis that these objects are young and that the radio source is still developing/expanding within the host galaxy itself.Very young radio sources must have the peak in their radio spectra occurring above a few tens of gigahertz, and for this reason they are termed high frequency peakers (HFPs). These newly born radio sources must be very rare given that they spend very little time in this stage. Ho = 100 km s−1 Mpc−1 and qo = 0.5 are used throughout this paper.

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17

Keenan, Jan. "Radio frequency catheter ablation". Nursing Standard 9, n. 10 (30 novembre 1994): 50–51. http://dx.doi.org/10.7748/ns.9.10.50.s50.

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18

Truszkiewicz, Adrian, David Aebisher, Zuzanna Bober, Łukasz Ożóg e Dorota Bartusik-Aebisher. "Radio Frequency MRI coils". European Journal of Clinical and Experimental Medicine 18, n. 1 (2020): 24–27. http://dx.doi.org/10.15584/ejcem.2020.1.5.

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Introduction. Magnetic Resonance Imaging (MRI) coils technology is a powerful improvement for clinical diagnostics. This includes opportunities for mathematical and physical research into coil design. Aim. Here we present the method applied to MRI coil array designs. Material and methods. Analysis of literature and self-research. Results. The coils that emit the radiofrequency pulses are designed similarly. As much as possible, they deliver the same strength of radiofrequency to all voxels within their imaging volume. Surface coils on the other hand are usually not embedded in cylindrical surfaces relatively close to the surface of the body. Conclusion. The presented here results relates to the art of magnetic resonance imaging (MRI) and RF coils design. It finds particular application of RF coils in conjunction with bore type MRI scanners.

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19

WANG, XIAOBIN. "RADIO FREQUENCY MAGNETIZATION NONVOLATILITY". SPIN 02, n. 03 (settembre 2012): 1240009. http://dx.doi.org/10.1142/s2010324712400097.

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Long time magnetization thermal switching under small amplitude high frequency excitation is analyzed. Approaches based upon conventional time-dependent energy barrier are not sufficient to describe magnetization nonvolatility under GHz excitations. Methods based upon large angle nonlinear magnetization dynamics are developed for both coherent and noncoherent magnetization switching. This dynamic approach is not only important for fundamental understanding of magnetization dynamics under combined radio frequency excitations and thermal fluctuations, but also critical for practical design of emerging spintronic devices. When applied to spin torque random access memory read operations, as sensing current duration reaches nanosecond, dynamic approach gives a switching probability estimation orders of magnitude different from that obtained from conventional time-dependent energy barrier approach.

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20

Wilson, J. F. "Computer radio-frequency interference". Electronics and Power 31, n. 2 (1985): 112. http://dx.doi.org/10.1049/ep.1985.0092.

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21

Kaye, A., J. Jacquinot, P. Lallia e T. Wade. "Radio-Frequency Heating System". Fusion Technology 11, n. 1 (gennaio 1987): 203–34. http://dx.doi.org/10.13182/fst11-203-234.

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22

Schmidt, D. R., C. S. Yung e A. N. Cleland. "Nanoscale radio-frequency thermometry". Applied Physics Letters 83, n. 5 (4 agosto 2003): 1002–4. http://dx.doi.org/10.1063/1.1597983.

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23

Jones, Alex K., Swapna Dontharaju, Shenchih Tung, Leo Mats, Peter J. Hawrylak, Raymond R. Hoare, James T. Cain e Marlin H. Mickle. "Radio frequency identification prototyping". ACM Transactions on Design Automation of Electronic Systems 13, n. 2 (2 aprile 2008): 1–22. http://dx.doi.org/10.1145/1344418.1344425.

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24

Rundh, Bo. "Radio frequency identification (RFID)". Marketing Intelligence & Planning 26, n. 1 (8 febbraio 2008): 97–114. http://dx.doi.org/10.1108/02634500810847174.

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25

Roome, S. J. "Digital radio frequency memory". Electronics & Communications Engineering Journal 2, n. 4 (1990): 147. http://dx.doi.org/10.1049/ecej:19900035.

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26

Padamsee, Hasan S. "Superconducting Radio-Frequency Cavities". Annual Review of Nuclear and Particle Science 64, n. 1 (19 ottobre 2014): 175–96. http://dx.doi.org/10.1146/annurev-nucl-102313-025612.

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27

Hingley, Martin, Susan Taylor e Charlotte Ellis. "Radio frequency identification tagging". International Journal of Retail & Distribution Management 35, n. 10 (11 settembre 2007): 803–20. http://dx.doi.org/10.1108/09590550710820685.

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28

Widmann, W. D., W. W. L. Glenn, L. Eisenberg e A. Mauro. "RADIO-FREQUENCY CARDIAC PACEMAKER*". Annals of the New York Academy of Sciences 111, n. 3 (15 dicembre 2006): 992–1006. http://dx.doi.org/10.1111/j.1749-6632.1964.tb53169.x.

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29

Kuzikov, S. V., A. V. Savilov e A. A. Vikharev. "Flying radio frequency undulator". Applied Physics Letters 105, n. 3 (21 luglio 2014): 033504. http://dx.doi.org/10.1063/1.4890586.

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30

Margaryan, A., R. Carlini, R. Ent, N. Grigoryan, K. Gyunashyan, O. Hashimoto, K. Hovater et al. "Radio frequency picosecond phototube". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 566, n. 2 (ottobre 2006): 321–26. http://dx.doi.org/10.1016/j.nima.2006.07.035.

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31

Tucker, Robert D., Chester E. Sievert, J. A. Vennes e Stephen E. Silvis. "Endoscopic radio frequency electrosurgery". Gastrointestinal Endoscopy 36, n. 4 (luglio 1990): 412–13. http://dx.doi.org/10.1016/s0016-5107(90)71082-6.

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32

Melski, Adam, Lars Thoroe e Matthias Schumann. "RFID – Radio Frequency Identification". Informatik-Spektrum 31, n. 5 (5 agosto 2008): 469–73. http://dx.doi.org/10.1007/s00287-008-0267-8.

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33

Roberts, C. M. "Radio frequency identification (RFID)". Computers & Security 25, n. 1 (febbraio 2006): 18–26. http://dx.doi.org/10.1016/j.cose.2005.12.003.

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34

Zeibig, Stefan. "Radio Frequency Identification (RFID)". Controlling 18, n. 1 (2006): 51–52. http://dx.doi.org/10.15358/0935-0381-2006-1-51.

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35

Ivannikov, V. I., Yu D. Chernousov e I. V. Shebolaev. "Radio-frequency power compressor". Technical Physics 44, n. 1 (gennaio 1999): 108–9. http://dx.doi.org/10.1134/1.1259261.

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36

Dobson, Tatyana, e Elle Todd. "Radio frequency identification technology". Computer Law & Security Review 22, n. 4 (gennaio 2006): 313–15. http://dx.doi.org/10.1016/j.clsr.2006.05.008.

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37

Wiltshire, M. C. K. "Radio frequency (RF) metamaterials". physica status solidi (b) 244, n. 4 (aprile 2007): 1227–36. http://dx.doi.org/10.1002/pssb.200674511.

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38

Deng, Shouyun, Zhitao Huang, Xiang Wang e Guangquan Huang. "Radio Frequency Fingerprint Extraction Based on Multidimension Permutation Entropy". International Journal of Antennas and Propagation 2017 (2017): 1–6. http://dx.doi.org/10.1155/2017/1538728.

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Radio frequency fingerprint (RF fingerprint) extraction is a technology that can identify the unique radio transmitter at the physical level, using only external feature measurements to match the feature library. RF fingerprint is the reflection of differences between hardware components of transmitters, and it contains rich nonlinear characteristics of internal components within transmitter. RF fingerprint technique has been widely applied to enhance the security of radio frequency communication. In this paper, we propose a new RF fingerprint method based on multidimension permutation entropy. We analyze the generation mechanism of RF fingerprint according to physical structure of radio transmitter. A signal acquisition system is designed to capture the signals to evaluate our method, where signals are generated from the same three Anykey AKDS700 radios. The proposed method can achieve higher classification accuracy than that of the other two steady-state methods, and its performance under different SNR is evaluated from experimental data. The results demonstrate the effectiveness of the proposal.

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39

Krupar, Vratislav, Oksana Kruparova, Adam Szabo, Lynn B. Wilson, Frantisek Nemec, Ondrej Santolik, Marc Pulupa, Karine Issautier, Stuart D. Bale e Milan Maksimovic. "Radial Variations in Solar Type III Radio Bursts". Astrophysical Journal Letters 967, n. 2 (28 maggio 2024): L32. http://dx.doi.org/10.3847/2041-8213/ad4be7.

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Abstract Type III radio bursts are generated by electron beams accelerated at reconnection sites in the corona. This study, utilizing data from the Parker Solar Probe’s first 17 encounters, closely examines these bursts down to 13 solar radii. A focal point of our analysis is the near-radial alignment (within 5°) of the Parker Solar Probe, STEREO-A, and Wind spacecraft relative to the Sun. This alignment, facilitating simultaneous observations of 52 and 27 bursts by STEREO-A and Wind respectively, allows for a detailed differentiation of radial and longitudinal burst variations. Our observations reveal no significant radial variations in electron beam speeds, radio fluxes, or exponential decay times for events below 50 solar radii. In contrast, closer to the Sun we noted a decrease in beam speeds and radio fluxes. This suggests potential effects of radio beaming or alterations in radio source sizes in this region. Importantly, our results underscore the necessity of considering spacecraft distance in multispacecraft observations for accurate radio burst analysis. A critical threshold of 50 solar radii emerges, beyond which beaming effects and changes in beam speeds and radio fluxes become significant. Furthermore, the consistent decay times across varying radial distances point toward a stable trend extending from 13 solar radii into the inner heliosphere. Our statistical results provide valuable insights into the propagation mechanisms of type III radio bursts, particularly highlighting the role of scattering near the radio source when the frequency aligns with the local electron plasma frequency.

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40

Swagarya Lawrence Boaz, Godbless. "Designing of UHF- Radio Frequency Identification (RFID) Antenna". International Journal of Scientific Engineering and Research 1, n. 3 (27 marzo 2013): 33–35. https://doi.org/10.70729/1131106.

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41

Franklin, R. N. "The dual frequency radio-frequency sheath revisited". Journal of Physics D: Applied Physics 36, n. 21 (15 ottobre 2003): 2660–61. http://dx.doi.org/10.1088/0022-3727/36/21/010.

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42

Rani, Supriya. "Software Defined Radio in Radio Frequency Identification Applications". International Journal for Research in Applied Science and Engineering Technology 9, n. VII (20 luglio 2021): 1887–92. http://dx.doi.org/10.22214/ijraset.2021.36778.

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RFID is an important aspect of today's age because it boosts efficiency and convenience. It is used for a lot of applications that prevent thefts of automobiles and merchandise. In current times there have been continuous transitions from analog to digital systems where software is being used to define the waveforms and analog signal processing is being replaced with digital signal processing. In this paper, we have done a thorough literature survey and understood the working of how software-defined radio is implemented in radio frequency identification for a better BER performance.

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43

Fridman, P. "Radio frequency interference rejection in radio astronomy receivers". Astronomical & Astrophysical Transactions 19, n. 3-4 (dicembre 2000): 625–45. http://dx.doi.org/10.1080/10556790008238609.

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44

Ando, A., A. Komuro, T. Matsuno, K. Tsumori e Y. Takeiri. "Radio frequency ion source operated with field effect transistor based radio frequency system". Review of Scientific Instruments 81, n. 2 (febbraio 2010): 02B107. http://dx.doi.org/10.1063/1.3279306.

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45

Kim, Yong-Jin, e Chang-Won Jung. "Design of mobile Radio Frequency Identification (m-RFID) antenna". Journal of the Korea Academia-Industrial cooperation Society 10, n. 12 (31 dicembre 2009): 3608–13. http://dx.doi.org/10.5762/kais.2009.10.12.3608.

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46

Jallod, Uday E., Hareth S. Mahdi e Kamal M. Abood. "Simulation of Small Radio Telescope Antenna Parameters at Frequency of 1.42 GHz". Iraqi Journal of Physics (IJP) 20, n. 1 (1 marzo 2022): 37–47. http://dx.doi.org/10.30723/ijp.v20i1.726.

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The paper presents an overview of theoretical aspects of small radio telescope antenna parameters. The basic parameters include antenna beamwidth, antenna gain, aperture efficiency, and antenna temperature. These parameters should be carefully studied since they have vital effects on astronomical radio observations. The simulations of antenna parameters were carried out to assess the capability and the efficiency of small radio telescopes to observe a point source at a specific frequency. Two-dimensional numerical simulations of a uniform circular aperture antenna are implemented at different radii. The small diameter values are chosen to be varied between (1-10) m. This study focuses on a small radio telescope with a diameter of 3 m since this telescope is very common in the world. The simulated results of this study illustrated that the power pattern of a 3 m antenna has a half-power beamwidth of approximately 5 degrees. Also, the maximum peak antenna temperature is estimated to be more than 3000 K. All of these results were in good agreement with observations of the neutral hydrogen spectral line at the frequency of 1.42 GHz using a small radio telescope.

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47

Gans, T., J. Schulze, D. O’Connell, U. Czarnetzki, R. Faulkner, A. R. Ellingboe e M. M. Turner. "Frequency coupling in dual frequency capacitively coupled radio-frequency plasmas". Applied Physics Letters 89, n. 26 (25 dicembre 2006): 261502. http://dx.doi.org/10.1063/1.2425044.

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48

Shuaibu-Sadiq, Munirah, e F. I. Anyasi. "Analysis of radio frequency spectrum usage using cognitive radio". Journal of Electrical, Control and Telecommunication Research 1 (29 luglio 2020): 1–8. http://dx.doi.org/10.37121/jectr.vol1.111.

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This paper presents the analysis of radio frequency (RF) spectrum usage using cognitive radio. The aim was to determine the unused spectrum frequency bands for efficiently utilization. A program was written to reuse a range of vacant frequency with different model element working together to produce a spectrum sensing in MATLAB/Simulink environment. The developed Simulink model was interfaced with a register transfer level - software defined radio, which measures the estimated noise power of the received signal over a given time and bandwidth. The threshold estimation performed generates a 1\0 output for decision and prediction. It was observed that some spectrum, identified as vacant frequency, were underutilized in FM station in Benin City. The result showed that when cognitive radio displays “1” output, which is decision H1, the channel is occupied and cannot be used by the cognitive radio for communication. Conversely, when “0” output (decision H0) is displayed, the channel is unoccupied. There is a gradual decrease in the probability of detection (Pd), when the probability of false alarm (Pfa) is increased from 1% to 5%. In the presence of higher Pfa, the Pd of the receiver maintains a high stability. Hence, the analysis finds the spectrum hole and identifies how it can be reused

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49

Taylor, Fred, Evan Gattis, Lucca Trapani, Dennis Akos, Sherman Lo, Todd Walter e Yu-Hsuan Chen. "Software Defined Radio for GNSS Radio Frequency Interference Localization". Sensors 24, n. 1 (22 dicembre 2023): 72. http://dx.doi.org/10.3390/s24010072.

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The use of radio direction finding techniques in order to identify and reject harmful interference has been a topic of discussion both past and present for signals in the GNSS bands. Advances in commercial off-the-shelf radio hardware have led to the development of new low-cost, compact, phase coherent receiver platforms such as the KrakenSDR from KrakenRF whose testing and characterization will be the primary focus of this paper. Although not specifically designed for GNSSs, the capabilities of this platform are well aligned with the needs of GNSSs. Testing results from both benchtop and in the field will be displayed which verify the KrakenSDR’s phase coherence and angle of arrival estimates to array dependent resolution bounds. Additionally, other outputs from the KrakenSDR such as received signal strength indicators and the angle of arrival confidence values show strong connections to angle of arrival estimate quality. Within this work the testing that will be primarily presented is at 900 MHz, with results presented from a government-sponsored event where the Kraken was tested at 1575.42 MHz. Finally, a discussion of calibration of active antenna arrays for angle of arrival is included as the introduction of active antenna elements used in GNSS signal collection can influence angle of arrival estimation.

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El Misilmani, H. M., M. Y. Abou-Shahine, Y. Nasser e K. Y. Kabalan. "Recent Advances on Radio-Frequency Design in Cognitive Radio". International Journal of Antennas and Propagation 2016 (2016): 1–16. http://dx.doi.org/10.1155/2016/9878475.

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Abstract (sommario):

With the growth of mobile data applications, the spectrum allocation is becoming very scarce. To ease congestion and boost speeds, cognitive radio (CR) is currently seen as a major solution and expected to be the key player in the new wireless technologies. In this paper, we will start by introducing the cognitive radio systems, followed by exploring the challenges in designing RF engine, along with an investigation of its antennas, amplifiers, oscillators, and the components that are expected to operate over a wide range of frequencies.

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