Ultra High Frequency Band Research Articles

First Detection of the Enigmatic Low Latitude 150‐km Echoes in the UHF Band

AbstractThrough applying a 4‐MHz linear frequency modulation waveform, which has high range resolution and signal intensity, we successfully detected for the first time the ionospheric 150‐km echo enhancement at 430–450 MHz of the Ultra‐High‐Frequency (UHF) band using the newly built Sanya Incoherent Scatter Radar (SYISR). The obtained low signal enhancement (less than 0.5 dB) explains why previous UHF experiments did not detect them. We also found that our measured fine structure shows a much wider forbidden region than previous results and covers a much larger altitudinal and local time region. In comparison with recent upper‐hybrid instability theory and simulation, our results confirmed the predicted higher altitude occurrence, wider gaps between enhancements, the turn corner feature around sunrise, and perhaps the weak enhancement, which provide an independent evaluation of the newly proposed mechanism in UHF band. Future UHF experiments could further improve the physical understanding of 150‐km echo phenomenon.

Electromagnetic properties of coal using microstrip and an algorithm based on the Nicolson-Ross-Weir method

The work implements an experimental methodology to find the dielectric parameters: electrical permittivity, effective permittivity, magnetic permeability, conductivity, absorption coefficient, impedance, and loss tangent of bituminous coal from the municipality of Morcá and Tópaga belonging to the Sogamoso-Jericó sub-basin of the Guaduas formation, one of the most important coal reserves in Colombia. The methodology, known for its efficiency, includes constructing a microstrip-type circuit, measuring scattering parameters or S-parameters at frequencies between 300 kHz and 1 GHz with a vector network analyzer, and extracting electromagnetic properties using the Nicolson-Ross-Weir algorithm. The implemented algorithm allowed us to see the behavior of the coal in a fraction of the ultra-high frequency band and to find quickly and easily the approximate values of the parameters as a function of frequency, which are very important for investigations in mathematical modeling and computational electromagnetics. The results show that the real and imaginary components of the relative dielectric permittivity decrease with increasing frequency, and the absorption coefficient and the loss tangent of the coal increase as a function of frequency, indicating that the coal behaves as a dissipative dielectric.

Low profile cavity-embedded ultra-wideband UHF array antenna with end-fire beams

A low profile, vertically polarized, ultra-wideband array antenna with end-fire beams operating in an ultra-high frequency (UHF) band is developed in this paper. The array antenna consists of 1×16 log-periodic top-hat loaded monopole antenna arrays and is feasible to embed into a shallow cavity to further reduce the array height. Capacitance is introduced in the proposed antenna element to reduce profile height and the rectangular top hats are carefully designed to minimize the transverse dimension. Simulated results show that when the antenna array operates in a frequency range of 300 MHz–900 ​MHz, the end-fire radiation pattern achieves ±45° scanning range in the horizontal plane. Then prototypes of the proposed end-fire antenna element and a uniformly spaced linear array (1×2) are fabricated and validated. The end-fire antenna array should be suitable for airborne applications where low profile and conformal scanning phased antenna arrays with end-fire radiations are required. This design is attractive for airborne platform applications that are used to search, discover, identify, and scout the aerial target with vertically polarized beams.

Novel printed passive ultra high frequency radio frequency identification antenna using meander technique

<p>In this paper, a novel radio frequency identification (RFID) antenna using a meander technique associated with a slotted patch is studied for RFID applications in the ultra high frequency (UHF) band [867.5-868 MHz]. The proposed RFID antenna is designed on a Kapton substrate with dielectric constant 3.5 and loss of 0.0027. It consists of two opposite meander line antennas of 8 turns each one and interconnected to ALIEH H3 microchip associated to two slotted patch’s with a global size 105×25×0.1 mm<sup>3</sup>. The proposed RFID antenna is designed and simulated using CST MWS as an electromagnetic solver. The results of the simulation show a return loss of -22.64 dB at 868 MHz, a reading distance of around 5 m, and a simulated input impedance of the antenna are 31.72+j109.68 Ω at the operating frequency 868 MHz.</p>

A spaceborne broadband circularly polarized conformal antenna for UHF band applications

AbstractA Spaceborne broadband circularly polarized conformal antenna for ultra high frequency band is presented. The antenna mounted on the outer surface of the circular arc spherical cone satellite works in 390–450 MHz frequency band, and has the characteristics of broadband, light miniature. The measured results for the antenna demonstrate an impedance bandwidth of 32.5% from 360 to 500 MHz, an axial ratio bandwidth of 27.2% from 380 to 500 MHz, and a peak gain of 6.7 dBic. The antenna form can be applied to the field of broadband circularly polarized conformal antenna on satellite and missile, and has a wide application prospect.

A Novel Antenna Design of Compact HF and UHF Passive RFID Tags with Interconnected Structure for Energy Harvesting and Tracking Systems

We propose a new dual-band passive RFID tag antenna design by combining a rectangular spiral coil and patch-meander-line dipole with an interconnected structure. This design enables operation in high-frequency (HF) and ultra-high-frequency (UHF) RFID systems, suitable for energy harvesting and tracking applications. The simulations by the CST full-wave software demonstrate conjugate impedance matching between the tag antenna and two RFID tag chips. At 13.56 MHz (HF), the tag antenna exhibits an inductive reactance of 422.79 Ω, while at 922.5 MHz (UHF), it presents an impedance of 9.41+j174.96 Ω. The antenna generates a maximum magnetic field intensity of 0.5 A/m and omnidirectional electromagnetic fields with an antenna realized gain of -4.26 dBi at 922.5 MHz. We also analyze the impact of the tag antenna combination using numerical software. Furthermore, we fabricate a prototype tag antenna and validate its performance with RFID readers. The proposed tag antenna achieves the maximum read ranges of 11 cm and 6.9 m for the HF (13.56 MHz) and UHF (920-925 MHz) bands, respectively, accompanied by the energy harvesting of 1.48 volts at the HF band by the coupling magnetic field received by the HF antenna to the chip ST25DV04K at the output voltage pin.

Evaluation of low-loss alumina material for high-power RF windows

Conventional RF vacuum windows are made of metalized ceramics, hermetically brazed to a pillbox cavity. High-power windows, operating in ultra-high frequency (UHF) band, require the fabrication of ceramic disks with diameters on the order of 9”. Furthermore, a Titanium Nitride (TiN) multipactor suppression coating must be applied to the ceramic surfaces. The large size and complex internal geometry of these windows create challenges in validating the coating in the fully fabricated assembly. This study evaluates a novel low-loss alumina AO479U, provided by Kyocera, and a reactive sputtering process suitable to deposit a 10-20 nm thick TiN coating on a large diameter window. The paper will report the changes in the TiN coating through chemical cleaning and vacuum braze processes using stylus profilometry, optical microscopy, Scanning Electron Microscopy (SEM), and Rutherford Backscattering Spectroscopy (RBS).

UHF Textronic RFID Transponder with Bead-Shaped Microelectronic Module

The idea of novel antennas and matching circuits, developed for radio frequency identification (RFID) passive transponders, and made on textile substrates, is presented in this paper. By manufacturing an RFID transponder by the means used in every clothing factory, we developed the concept of RFIDtex tags, which, as textronic devices, make a new significant contribution to the Internet of Textile Things (IoTT). The main feature of the device consists of the use of an uncommon inductively coupled system as the antenna feed element. The antenna is sewn/embroidered with a conductive thread, and the microelectronic module with an RFID chip is made in the form of a bead, using standard electronic technology. Finally, the construction of the RFIDtex tag is developed for easy implementation in production lines in the garment industry. The proposed inductive coupling scheme has not been considered anywhere, so far. The developed transponder is dedicated to operating in RFID systems of the ultra-high frequency band (UHF). The numerical calculations confirmed by the experimental results clearly indicate that the proposed coupling system between the antenna and the microelectronic module works properly and the RFIDtex device can operate correctly within a distance of several meters. The proposed design is based on the authors’ patent on the textronic RFID transponder (patent no PL 231291 B1).

5G-RCOLAB: A system level simulator for 5G and beyond in rural areas

This paper describes 5G-RCOLAB, an open source simulation tool for performance evaluation of 5G/6G wireless networks in rural areas. The tool is designed with a layered architecture, based on three modules: (i) a link-level simulator of a communication channel for remote areas, with a mapping Link to System (L2S) interface; (ii) a Long-Term Evolution (LTE)-based physical layer adapted for remote areas, together with a Medium Access Control (MAC) layer that includes a novel Collaborative Spectrum Sensing (CSS) technique with security features for Byzantine attacks and spectrum usage efficiency; and (iii) an application oriented network layer that emulates the behavior of typical users in rural areas. The tool has the goal to reduce simulation complexity of large scale 5G rural networks and at the same time, to represent coherently the features of the physical and MAC layers, that include new channel models that cover long distances with the use of TV White Spaces (TVWS) in the Ultra High Frequency (UHF) and Very High Frequency (VHF) bands, as well as novel CSS techniques to improve spectrum efficiency. The 5G-RCOLAB was validated both by field test measurements from a Proof of Concept (PoC) prototype and by the simulation and evaluation of three 5G common core use cases in rural areas. The results show that the 5G-RCOLAB features allow a better evaluation of novel technologies implemented in the physical and MAC layers and provide paths for improvements and deployments of cost effective solutions of 5G in rural or remote areas.

Satellite radio detection via dual-microwave Rydberg spectroscopy

Rydberg electric field sensors exploit the large number of Rydberg resonances to provide sensitivity over a broad range of the electromagnetic spectrum. However, due to the difficulty of accessing resonant Rydberg states at ultra-high frequency (UHF) and below, ubiquitous bands in the world's current wireless communications infrastructure, they currently fall, short in sensitivity in this range. We present a resonant Rydberg electric field sensor operating in the UHF band using a dual-optical dual-microwave spectroscopy scheme. Adding an additional microwave photon allows us to access transitions between Rydberg states with higher angular momentum (L=3→4), which have lower resonant frequencies than transitions typically used in Rydberg sensors. We discuss the applicability of this type of sensor across the UHF band and below and measure the resonant sensitivity of our system at 2.3 GHz to be 70(5) μV m−1 Hz−1∕2, 57 times better than the measured sensitivity with a far off-resonant probing scheme at this frequency. We also show the effectiveness of this sensing scheme by measuring Sirius XM satellite radio (2.320–2.345 GHz) received outside the laboratory and rebroadcast onto the atoms.

Design and measurement of the receiving antenna for electromagnetic field energy harvesting in UHF band

This paper aims to design a receiving antenna for harvesting energy using the wireless energy transfer method based on the ultra-high frequency (UHF) band. The study was conducted by comparing four types of the receiving antenna design. A mathematical and experimental analysis has been done to evaluate the performance of the designed antennas. A Yagi-Uda antenna is utilized as the transmitter. The results show that the zig-zag type antenna has the best performance. It can receive electromagnetic energy from a transmitter with maximum efficiency is 0.1% for the receiving antenna volume of 0.34 cm<sup>3</sup>. The proposed method can meet the energy necessity of an implant device with a charging time of approximately 21.61 hours for the 700 mAh rechargeable battery capacity. As our preliminary conclusion, based on our results, this proposed method can be used as a reference for the practice in the WET field and the medical and restricted areas in the electromagnetic energy harvesting case.

Folded-core radar-absorbing sandwich composite with sendust particle-added Ni-plated glass/polyether ether ketone thermoplastic resin in the ultrahigh-frequency band

A novel lightweight folded-core radar-absorbing sandwich composite composed of Ni-plated glass fiber/polyether ether ketone (PEEK) and sendust-particle-filled polyurethane (PU) foam thermoplastic resin is presented. It is designed as a V-pattern folded-core unit cell, which can lead to gradual loss of the incident radar signal intensity and enhanced radio wave absorption performance in the ultra-high frequency (UHF) band (0.3–3.0 GHz). Ni-plated glass fiber was prepared by an electroless plating technique, and a folded-core radar-absorbing sandwich composite by a stamp-forming process. The folded-core was decorated with sendust-particle-filled PU foam to enhance radio wave absorption performance. The radio wave absorption performance of the folded-core sandwich composite was measured using a proposed UHF band single-port free space measurement system. The proposed sandwich composite with a thickness of 81.6 mm achieves a reflection loss below −10 dB (90% absorption) and bandwidth covers in the frequency range of 0.9–3 GHz while maintaining a low density of 0.142 g/cm3. This study presents the new radar-absorbing sandwich composite with a UHF absorber as a low-frequency band, a low density, and excellent radio wave absorption performance.

Effect of chlorination with carbon tetrachloride on the interaction of carbon fibers with electromagnetic radiation in the ultrahigh-frequency band

Effect of chlorination with carbon tetrachloride on the interaction of carbon fibers with electromagnetic radiation in the ultrahigh-frequency band

Ultrawideband lightweight absorber based on composite strategy with active control of absorption in the UHF band

In this paper, a composite strategy has been developed to achieve continuous absorption coverage from the ultrahigh-frequency (UHF) band to the Ku band. Based on this strategy, an ultrawideband lightweight composite metamaterial absorber is fabricated and measured. The composite absorber comprises two cascaded parts operating in separated frequency bands. First, we design a polarization-insensitive tunable absorber in the UHF band based on the equivalent circuit model. The measured results indicate that the tunable UHF absorber obtains a tunable −10 dB reflection coefficient from 0.88 to 1.48 GHz. Furthermore, a lightweight 3D absorber is applied to cascade with the tunable UHF absorber to constitute a ultrawideband composite absorber. The composite absorber achieves an ultrawideband absorption ranging from 0.78 to 18 GHz with a reflection coefficient below −10 dB. The overall composite structure is extremely lightweight with a surface density below 0.2897 g cm−2. This composite absorber also exhibits good angular stability, low profile, and polarization insensitiveness. We think this work is of great application potential for military and civilian applications.

Low-Profile Antenna System for Cognitive Radio in IoST CubeSat Applications

Since the CubeSats have become inherently used for the Internet of space things (IoST) applications, the limited spectral band at the ultra-high frequency (UHF) and very high frequency should be efficiently utilized to be sufficient for different applications of CubeSats. Therefore, cognitive radio (CR) has been used as an enabling technology for efficient, dynamic, and flexible spectrum utilization. So, this paper proposes a low-profile antenna for cognitive radio in IoST CubeSat applications at the UHF band. The proposed antenna comprises a circularly polarized wideband (WB) semi-hexagonal slot and two narrowband (NB) frequency reconfigurable loop slots integrated into a single-layer substrate. The semi-hexagonal-shaped slot antenna is excited by two orthogonal +/−45° tapered feed lines and loaded by a capacitor in order to achieve left/right-handed circular polarization in wide bandwidth from 0.57 GHz to 0.95 GHz. In addition, two NB frequency reconfigurable slot loop-based antennas are tuned over a wide frequency band from 0.6 GHz to 1.05 GH. The antenna tuning is achieved based on a varactor diode integrated into the slot loop antenna. The two NB antennas are designed as meander loops to miniaturize the physical length and point in different directions to achieve pattern diversity. The antenna design is fabricated on FR-4 substrate, and measured results have verified the simulated results.

Radio Frequency Energy Harvesting-Based Self-Powered Dairy Cow Behavior Classification System

Dairy cow behavior is closely related to the cow’s health and physiological status. Automatic diagnosis and precision dairy farming are achieved by intelligent behavior recognition. We propose a self-powered system to classify various dairy cow behaviors based on acceleration data to obtain a novel and effective solution for dairy cow behavior monitoring. A neck-mounted sensor tag integrated with an accelerometer is used to record dairy cow behavior. The sensor tag operates without any batteries. Energy is harvested from radio frequency (RF) waves at the ultrahigh-frequency band of 915 MHz emitted by a reader. The device can initiate receiving power for conversion at input powers as low as −8 dBm. The maximum achievable power conversion efficiency (PCE) is 54.5%. The sensor tag consumes only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$53 \mu \text{A}$ </tex-math></inline-formula> of low average current with a sampling frequency of 10 Hz to acquire acceleration data and backscatter them to the reader. Dairy cow behaviors were observed and recorded for 14 days, with three behaviors selected for the following classification: standing, walking, and grazing. Two deep learning models are developed to classify these behaviors, including a 1-D convolutional neural network (1D-CNN) and long short-term memory (LSTM). The collected data were divided into 12-s windows, which were used as input to classifiers. The walking behavior is most accurately recognized in both models (95.56% with 1D-CNN and 92.15% with LSTM), and the best classification accuracy of 94.35% is achieved from the 1D-CNN model.

Wearable Ungrounded Tag Antenna for UHF RFID Applications

A single-layer ungrounded tag antenna is designed for on-body radio frequency identification (RFID) applications in the ultrahigh frequency (UHF) band. The ungrounded tag antenna is designed based on a broadside radiating Huygens source. The electric dipole is generated by the center part of an original dipole, while two orthogonal magnetic dipoles are created by stacking another two metallic strips at the edge of the original dipole. The tag antenna shows good robustness of input matching and radiation efficiency with respect to the human-body effect. Furthermore, the designed tag antenna is also able to work with metallic objects and its resonant frequency is stable around 920 MHz. Finally, three tag prototypes, including the proposed tag antenna, are fabricated and tested. The measured reading range confirms the numerical simulations and demonstrates the robustness of the proposed design with respect to different distances between human-body and tag antenna. The proposed tag provides a reading range of 5.0 m (near-body), 8.0 m (free space), and 16.5 m ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200\times200$ </tex-math></inline-formula> mm metallic plate), respectively.

Simple VHF and UHF Propagation Loss Model

Empirical propagation loss models play a crucial role in a wireless communication system with their cost-effectiveness and simplicity. In this letter, we present a mathematical characterization of the Federal Communication Commission (FCC) F(50,50) curve for the Very High Frequency (VHF) and the Ultra High Frequency (UHF) band. The proposed empirical model is based on a novel step-wise curve fitting the FCC signal strength data. The F(50,50) model is intended for the TV broadcasting system and has been employed effectively in different literary works. Following this, we proposed a simple mathematical expression applicable to a 100 km distance with antenna height ranging from 30 to 300 m. The results showed that the proposed mathematical formulation agreed well with the F(50,50) curve data. Furthermore, the model presented is straightforward and can readily be implemented in VHF and UHF signal loss calculation requiring minimal input parameters.

Systematic design and prototyping of a low‐cost passive UHF‐RFID transponder

AbstractThis paper presents a methodical design and prototyping of a passive European ultra‐high frequency (UHF) band radio frequency identification (RFID) transponder. The transponder has a 70 × 17 × 0.3 mm3 copper antenna whose design is based on the folded dipole architecture and utilizes techniques such as meandering and end loading to match a Texas Instruments (TI) UHF‐RFID chip through a T‐match feeding network. The tag's simulated and measured performances indicate good coverage of the entire UHF band with a return loss better than 10 dB. The transponder was then fabricated using inexpensive off‐the‐shelf materials and its performance was tested. The proposed tag achieved good gain, read range, and cost efficiency when compared with current folded dipole antennas and can be easily adapted for various applications such as supply chain, access or security, and vehicle identification.

A dual‐frequency inverted‐F antenna for UAVs transceiver application

AbstractA dual‐frequency inverted‐F antenna operating in the ultrahigh frequency band is presented. The proposed antenna includes an inverted F‐shaped radiator and a dual‐frequency loading circuit. The dual‐frequency loading circuit is located between the short pin and the ground. The dual‐frequency loading circuit presents a short‐circuit state at the low‐frequency band and an open‐circuit state at the high‐frequency band. By introducing the dual‐frequency loading circuit, the proposed antenna possesses dual‐frequency performance compared with the traditional inverted‐F antenna. The resonant frequencies of the proposed antenna can be controlled by adjusting the component values of the dual‐frequency loading circuit. A prototype was fabricated and measured to validate the method. The height of the fabricated antenna is 40 mm at 713 MHz. The bandwidths of the fabricated prototype are 713–779 MHz and 858–920 MHz. The proposed antenna possesses vertical polarization, which shows that the proposed antenna has broad application prospects in unmanned aerial vehicles communication systems.