Ultra High Frequency Band Research Articles

Compact Planar Loop–Dipole Composite Antenna With Director for Bandwidth Enhancement and Back Radiation Suppression

A wideband and unidirectional loop-dipole composite antenna with a planar structure is proposed. The antenna includes a half-wavelength dipole and a one-wavelength loop that are printed on different sides of a substrate. To control the radiation characteristics of each element separately, the dipole is fed using a coaxial cable, whereas the loop is fed using offset broad-side coupling. To overcome the low front-to-back ratio (FBR) at lower and upper frequencies of the band, where the loop-dipole mode is not dominant, while maintaining a compact size, a parasitic strip is located in the vicinity of the loop. The strip acts as a director for the dipole at the low frequencies and for the loop at the high frequencies and thus significantly improves the FBR at those frequencies. The antenna achieves a wide fractional operating bandwidth of 49% at 0.7-1.15 GHz, a size reduction of more than 50% compared with recent similar designs, stable gain with a peak value of 4.8 dBi, and a minimum FBR of 11 dB across the operating bandwidth. Owing to its compact and planar structure, lightweight, simple fabrication, and stable radiation characteristic, it can be utilized in various wireless applications operating at the ultrahigh-frequency band.

An Improvement on SSA Method for EM Scattering From Electrically Large Rough Sea Surface

An improved facet model for the predication of the normalized radar cross section (NRCS) of electrically large rough sea surface was proposed based on the first-order small slope approximation (SSA-1) method, the Bragg scattering mechanism, and the specular scattering mechanism. The proposed method is able to evaluate both the complex reflective function and NRCS of electrically large sea surfaces from as low as ultrahigh frequency band to as high as Ka-band. The main idea is that a tilt sea facet can be regarded as the superposition of a planner facet and the microscopic profile; the latter is assumed to be a set of sinusoidal ripple patches. Thus, the integration kernel in SSA-1 over several small facets can be replaced by a large facet with a short wave modification. The efficiency increases because of the much larger mesh size than SSA. Then, both the backscattering and bistatic scattering NRCS results calculated by the proposed method were compared with those predicated by SSA-1, and all of the results show that the proposed method has the merits of high calculation efficiency as well as calculation accuracy.

Development of compact inductive coupled meander line RFID tag for near-field applications

The development of compact radio frequency identification (RFID) tag is the key requirement for wireless tracking of precious small size goods/packages in transport. A design of compact meander line tag antenna having inductive coupling feed is presented for RFID system operating at ultra high frequency band of865–867 MHz. The size of the proposed tag antenna is43 mm × 10 mm, and is designed using Higgs 4 IC chip (made Alien Technology, USA) having impedance of20.55− j191.45 Ωat centre frequency866 MHz.The antenna characteristics such as impedance, radiation pattern, bandwidth, and effect of ground on gain and tag size are analyzed and found to closely match with the simulated values. The observed value of reading range varies from87.5 to 35 cmsdepending on mounting on non-metal and metal packages, respectively.

STATISTICAL ANALYSIS FOR TERENGGANU FORWARD SCATTER RADAR SEASIDE CLUTTER

The statistical analysis for Terengganu, Malaysia seaside clutter is presented in this paper. The measured clutter data were collected using a prototype of forward scatter radar (FSR) micro-sensor network with very high frequency (VHF) and ultra-high frequency (UHF) bands. Four categories of clutter strength were recorded during the measurements, which are low, medium, strong and very strong clutter. The classes were divided according to the wind speed occurred during the measurements period. The analysis is to determine the best-fit distribution model for the measured clutter data. Four types of distribution models are used in this analysis, which are Weibull, Gamma, Log-Logistic and Log-Normal distribution. One of the goodness of fit (GOF) tests called root mean square error (RMSE) is used to prove which distribution is a better fit to the probability distribution of the measured clutter data. The obtained results show that for 64 MHz with all clutter level strength, Weibull distribution provides better fit and records the lowest RMSE. Weibull distribution also fits best to the clutter data for low clutter of 151 MHz. However, for the rest of clutter level strength for 151 MHz, Gamma distribution is the best-fitted model with lowest RMSE values. Log-Logistic distribution proves to be the best fitted model to all clutter level strength of clutter data for 434 MHz with smallest RMSE values.

RFID tag antenna for ultra and super high frequency band applications

A novel dual-band antenna for radio frequency identification tag is proposed for ultra high frequency (UHF: 915 MHz) and super high frequency (SHF: 2450 MHz) bands. The proposed tag antenna is a single sided dual-antenna structure, designed on the grounded (metallic) dielectric substrate. The proposed tag antenna can be used on any kind of surfaces including metals without severe performance degradation due to its metallic ground plane. At UHF band, proposed tag antenna works as dual-antenna structure. In the dual-antenna structure, one antenna works for receiving and another for backscattering. Due to separate backscatterer, the maximum differential radar cross section improved and results in the enhancement of the maximum read range. Whereas at SHF band, proposed antenna works as conventional single antenna structure and during operations it switches between receiving and backscattering modes. The proposed antenna consists of a meandered line antenna and a rectangular patch antenna loaded with an F-shaped and an inverted L-shaped slots. The S-parameters are measured by means of differential probe technique. Simulated and measured results are observed in good agreement. The read range is observed about 5 and 6 m at 915 and 2450 MHz, respectively. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:640–650, 2016.

Low-loss Z-type hexaferrite (Ba3Co2Fe24O41) for GHz antenna applications

We report a low magnetic loss Ba3Co2Fe24O41 (Co2Z) hexaferrite for use in gigahertz (GHz) antennas. Acid-etching was very effective in removal of unwanted Y-type hexaferrite (Ba2Co2Fe12O22) from calcined Co2Z powder. It is found that the calcined and acid etched (AE) Co2Z hexaferrite shows a low magnetic loss tangent (tanδμ) of 0.012 and 0.037 at 1 and 2GHz, respectively. These low tanδμ are attributed to removal of Y-type hexaferrite, which possesses a lower anisotropy field (Hk) than W-type hexaferrite (BaCo2Fe16O27). The figure of merit (FOM) of the AE Co2Z hexaferrite is 141.7 and 48.7 at 1 and 2GHz, respectively. These FOM are much higher than the FOM of previously reported low-loss magnetic materials. Therefore, the AE Co2Z hexaferrite can be a good candidate for GHz antenna application in the ultra-high frequency (UHF) band.

Evaluation of transformer core contribution to partial discharge electromagnetic waves propagation

Accurate Partial Discharge (PD) measurement requires the expansion of the measurement frequency range to Ultra High Frequency (UHF) band. For this it is needed to implement modern techniques when monitoring an important element of power system, such as power transformer. Different kind of experimental models, such as insulation defect models, and the complete transformer windings models are used to simulate the partial insulation failure situations which occur in a real transformer. However, since in these models, some kind of simplifications are employed which may result in an electromagnetic waves (EM) propagation pattern different from what exists in a real transformer and encounter errors in its PD measurement results. In this paper, the transformer core effects on PD EM wave propagation are investigated. To address this concern, different core designs are simulated. Finite Integration Time (FIT) method is used for electric field calculation through application of Microsoft CST microwave studio Software. The probes recorded electric fields are analyzed using wavelet transform (WT). A new approach based on energy scale coefficient (for each decomposition level) is used for mother wavelet selection. Results of these simulations demonstrate how existence of core and its design affect the characteristics of measured PD signal.

2-SR-based electrically small antenna for RFID applications

In this work, the 2-turn spiral resonator (2-SR) is proposed as an electrically small antenna for passive radio frequency identification (RFID) tags at the European ultra-high frequency (UHF) band. The radiation properties are studied in order to explore the viability of the 2-SR applied to tag antenna design. Based on analytical calculations, the radiation pattern is found to provide a cancelation of the radiation nulls. This results in a mitigation of the blind spots in the read range, which are present in typical UHF-RFID tags as an undesired feature. As a proof of concept, a passive tag of size 35 mm × 40 mm (λ 0/10 × λ 0/9) based on the 2-SR antenna is designed and fabricated. Good radiation efficiency (75 %) and a quasi-isotropic radiation pattern are obtained. The experimental tag read range for different directions is in good agreement with the simulation results. The measured read range exhibits maximum and minimum values of 6.7 and 3.5 m, respectively.

Polarization and Effects on Hidden Node/Shadowing Margin for TVWS

Dual polarized measurements comparing the received power of a line of sight broadcast signal in the ultra-high frequency band with received power in suburban streets and indoors including high rise buildings are presented in this paper. Both the co-polarized and cross-polarized fades are therefore measured in the different locations. Their purpose is twofold: 1) to identify the importance of using polarization when considering hidden node margins in spectrum sensing of television white spaces and 2) to indicate how polarization can be beneficial in improving the shadowing margin to increase the path loss from the secondary to primary user and thus further protect digital terrestrial television receivers from harmful interference. The impact of polarization in open environments with low clutter or near windows inside high rise buildings is more significant than in densely cluttered spaces experiencing strong multipath.

Investigation of a stripline transmission line structure for gyromagnetic nonlinear transmission line high power microwave sources.

A stripline gyromagnetic nonlinear transmission line (NLTL) was constructed out of yttrium iron garnet ferrite and tested at charge voltages of 35 kV-55 kV with bias fields ranging from 10 kA/m to 20 kA/m. Typically, high power gyromagnetic NLTLs are constructed in a coaxial geometry. While this approach has many advantages, including a uniform transverse electromagnetic (TEM) mode, simple interconnection between components, and the ability to use oil or pressurized gas as an insulator, the coaxial implementation suffers from complexity of construction, especially when using a solid insulator. By moving to a simpler transmission line geometry, NLTLs can be constructed more easily and arrayed on a single substrate. This work represents a first step in exploring the suitability of various transmission line structures, such as microstrips and coplanar waveguides. The resulting high power microwave (HPM) source operates in ultra high frequency (UHF) band with an average bandwidth of 40.1% and peak rf power from 2 MW to 12.7 MW.

Eroding the assets of citizenship? From broadcast to broadband

The promise of convergence and the maturing internet appear to create arenas of communicative plenty but, instead of the end of spectrum scarcity, we are witnessing a new challenge of ‘coexistence’ and fierce competition over spectrum between the broadcasters and mobile telecom providers. Some European countries have already decided on further reductions in the broadcast spectrum, though the vast majority disagreed with the mobile industries’ proposal at the World Radiocommunication Conference in November 2015 that the entire ultra high frequency band should in future be shared by mobile broadband and broadcasting. This article explores the proposition that broadcasting requires adequate spectrum in order to deliver the information and cultural assets that are vital for citizenship, at a cost likely to remain significantly lower than comparable service delivered via subscription or broadband providers.

Diode‐switched thermal‐transfer printed antenna on flexible substrate

Diode-switching that can be used to introduce frequency agility into antennas produced by thermal transfer printing is demonstrated. The particular example is a triangular Sierpinski fractal pattern with two PIN diodes to switch between operation optimised for the 800 MHz ultra-high frequency (UHF) band (diodes on) and 2400 MHz ISM band (diodes off). Our measured results show an improvement in S 11 in the UHF band from −2 to −28 dB and from −7 to −30 dB at 2400 MHz, when switching the diodes appropriately. The measured bandwidth is 200 (1000) MHz, and the measured directivity is 3.1 dB (5.2 dB) while the measured gain is −5.2 dB (6.7 dB) for the diodes on (off).

Let's Make Them Cognitive Cognitive Radio Technology Applied to Professional Wireless Microphone Systems

In recent years, the ultra-high frequency (UHF) band from 470-862 MHz has been subject to several changes in frequency allocation, and a final decision for new services is still under discussion. Until 2010, this band was exclusively assigned to stations for terrestrial video broadcasting (DVB-T) [1]. The current demand for ever increasing data rates for mobile devices has led to changes in frequency range assignments. The key term digital dividend is frequently used by regulatory bodies and well-known in the cognitive radio community. In its first rollout, the band from 790-862 MHz was brought up for auction to mobile network operators in Germany [2]. The total revenue for 60 MHz of spectrum was ?3,575 billion [2], [3], which underlines the great market value of the radio spectrum.

PRINTED COMPACT LENS ANTENNA FOR UHF BAND APPLICATIONS

A new microwave lens antenna suitable for ultra-high frequency (UHF: 300 MHz-3 GHz) band applications is proposed. An improved bow-tie antenna and a planar metamaterial lens design is presented. 5 dB improvement in boresight gain and a directive radiation pattern is achieved with the lens. The application of the designed antenna is demonstrated in a ground penetrating radar (GPR) experiment. The size of the antenna is very compact compared to other antennas found in the literature used for similar applications.

Radar cross‐section measurement in millimetre‐wave for passive millimetre‐wave identification tags

The passive millimetre-wave identification (MMID) technology was introduced few years ago, exploiting the advantages of the passive ultra-high frequency (UHF) radio frequency identification (RFID). The communication is based on backscattering modulation, related to the radar cross-section (RCS) of the transponder. Thus, the need of accurate RCS measurement in the V-band arises. This work presents two methods to measure the RCS of any antenna in the particular case of MMID from 57 to 66 GHz. The studied methods require some precautions in millimetre-wave compared with measurements done in the UHF band. The two approaches highlight the methodology for accurate RCS measurement while the methods are evaluated through an example. A horn antenna is used as a MMID tag antenna and the RCS of the antenna is studied across three different loads as in UHF RFID: the short circuit, the open circuit and the matched load. The proposed methods provide a good accuracy and are validated by comparing the measurement results to the simulation.

Passive UHF RFID tag with multiple sensing capabilities.

This work presents the design, fabrication, and characterization of a printed radio frequency identification tag in the ultra-high frequency band with multiple sensing capabilities. This passive tag is directly screen printed on a cardboard box with the aim of monitoring the packaging conditions during the different stages of the supply chain. This tag includes a commercial force sensor and a printed opening detector. Hence, the force applied to the package can be measured as well as the opening of the box can be detected. The architecture presented is a passive single-chip RFID tag. An electronic switch has been implemented to be able to measure both sensor magnitudes in the same access without including a microcontroller or battery. Moreover, the chip used here integrates a temperature sensor and, therefore, this tag provides three different parameters in every reading.

Radio astronomy ultra-low-noise amplifier for operation at 91 cm wavelength in high RFI environment

An ultra-low-noise input amplifier intended for a use in a radio telescope operating at 91 cm wavelength is presented. The amplifier noise temperatures are 12.8 ± 1.5 and 10.0 ± 1.5 K at ambient temperatures of 293 and 263 K respectively. The amplifier does not require cryogenic cooling. It can be quickly put in operation thus shortening losses in the telescope observation time. High linearity of the amplifier (output power at 1 dB gain compression P1dB ≥ 22 dBm, output third order intercept point OIP3 ≥ 37 dBm) enables the telescope operation in highly urbanized and industrialized regions. To obtain low noise characteristics along with high linearity, high-electron-mobility field-effect transistors were used in parallel in the circuit developed. The transistors used in the amplifier are cost-effective and commercially available. The circuit solution is recommended for similar devices working in ultra-high frequency band.

Wearable Antennas for Off-Body Radio Links at VHF and UHF Bands: Challenges, the state of the art, and future trends below 1 GHz

An in-depth survey of wearable antennas for offbody radio links in the very high-frequency (VHF) and ultrahigh-frequency (UHF) bands (below 1 GHz) is presented. The review encompasses distinctive specifications, design criteria and challenges, material characterization procedures, antenna topologies and technologies, multiantenna systems, dedicated testing procedures, applications, and future trends.

Unidirectional Slot-Loaded Loop Antenna With Wideband Performance and Compact Size for Congestive Heart Failure Detection

A slot-loaded meandered loop antenna for congestive heart failure (CHF) detection system is presented. To meet the requirements for a CHF detection system, the antenna is designed to have a compact size, wideband at the ultra-high frequency band and unidirectional radiation. To that end, several techniques are applied to the main utilized structure, which is a conventional loop antenna. To lower the resonant frequency and enhance the directivity within a compact size, the loop is capacitively loaded using a pair of slots. To compensate for the effect of the capacitive coupling on the input impedance matching, an inductive reactance is added by meandering the loop’s structure. With the applied modifications, the proposed antenna has a compact size of ${0.21} \times 0.21$ with respect to the wavelength at the lowest operating frequency. The realized dimension represents only a quarter of the size of its counterpart planar designs. The proposed antenna achieves a wide measured fractional bandwidth of 50% (0.66–1.1 GHz), 9 dB peak front-to-back ratio and 4.1 dBi gain. The antenna is then used as part of a CHF detection system that also includes a compact transceiver, scanning platform, and laptop for control and processing. Using a suitable frequency–domain processing and imaging algorithm, the system successfully detects an early CHF in an artificial torso phantom.

Magnetorheological elastomers with efficient electromagnetic shielding

This study is concerned not only with an investigation of rheological performance of magnetorheological elastomers (MREs) with random distribution based on modified magnetic particles, but also discusses their electromagnetic shielding properties for the first time. The current work further highlights the necessity of magnetic particles protection against oxidation species affecting them in real application conditions. Two kinds of MREs differing in matrix type represented by silicone elastomer and thermoplastic elastomer are prepared, and pristine carbonyl iron (CI) particles and siloxane-modified CI particles were used for each matrix. The difference in magnetic properties after the modification of particles is negligible while the modification significantly improves the anti-acid-corrosion properties. Moreover, modification of particles surface enhances their compatibility with silicone elastomer matrix which is evidenced by the measurements of viscoelastic properties under the external magnetic field applied. It is also shown that all the developed MREs can be successfully applied for the absorption of electromagnetic radiation in ultra-high frequency band, namely the frequency range from 700MHz to 1.6GHz can be readily covered by these materials.