UHF Frequency Research Articles

The Effect of Refractivity on Propagation at UHF and VHF Frequencies

This paper is using weather parameters to investigate the effect of refractivity on propagation in the first kilometer of the atmosphere over the English Channel for a long transhorizon path of 140 km. Different refractivity profiles are constructed based on meteorological data taken from the UK Meteorological Office in order to investigate the effects of refractivity on propagation. The analysis is made for the hourly experimental path loss between the transmitter and receiver obtained from the experimental setup comprised of two communication links. The frequency of operation of the first link is 2015 MHz and that of the second link is 240 MHz. Parabolic equation method is modelled to get an hourly modelled path loss corresponding to each hourly experimental path loss to be analyzed for the said communication links. The correlation between the modelled path loss and experimental path loss is computed for refractivity distribution recommended by the ITU and predicted profiles. It is inferred from the simulated and experimental results that little or no influence exists by the evaporation duct upon path loss at 2015 MHz specifically for a long path of 140 km over the sea.

Cognitive Cellular Systems: A New Challenge on the RF Analog Frontend

AbstractCognitive Cellular Systems are seen today as one of the most promising ways of moving forward solving or at least easing the still worsening situation of congested spectrum caused by the growing number of users and the expectation of higher data transfer rates. As the intelligence of a Cognitive Radio system is located in the digital domain – the Cognitive Engine and associated layers – extensive research has been ongoing in that domain since Mitola published his idea in 1999. Since, a big progress has been made in the domain of architectures and algorithms making systems more efficient and highly flexible. The pace of this progress, however, is going to be impeded by hard requirements on the received and transmitted signal quality, introducing ultimate challenges on the performance of the RF analog frontend, such as in-band local oscillator harmonics, ultra low sensitivity and ultra high linearity. The RF frontend is thus likely to become the limiting technical factor in the true realization of a Cognitive Cellular System. Based on short recapitulations of the most crucial issues in RF analog design for Cognitive Systems, this article will point out why those mechanisms become responsible for the limitation of the overall performance particularly in a broadband Cognitive Cellular System. Furthermore, as part of a possible solution to ease the situation, system design of a high intermediate frequency (IF) to UHF frequency converter for cognitive radios is discussed and the performance of such a converter analyzed as a proof of concept. In addition to successfully tackling some of the challenges, such a high-IF converter enables white space operation for existing commercial devices by acting as frequency converter. From detailed measurements, the capabilities in both physical layer and application layer performance of a high-IF frontend developed out of off-the-shelf components is explained and is shown to provide negligible degradation to the commercial device being connected to.

High Frequency Properties of RF Planar Passive Components

This paper describes the different constructions of planar capacitors and inductors which are able to work up to UHF frequencies. Described passive components were manufactured using two different technologies: photolithography on polycarbonate film and on FR-4 substrate, screen printing technology. The high-frequency characteristics of the main electrical parameters (capacitance, inductance, quality factor and impedance) of passive components made using different technologies were measured and compared. Suitable finite element models of capacitors were created using multiplatform software applications COMSOL Multiphysics®. Based on obtained data the resonant circuits for wireless operating principle devices were designed and fabricated. Comparison of the calculated values of inductance, capacitance, and resonant frequency with measured data was made.

Study of UHF Frequency Response Characteristics of the Semicircle Dipole Inner Sensor for Partial Discharge Detection in GIS

The paper designed a semicircle dipole inner sensor for UHF partial discharge detection in GIS. By comparing the symmetric semicircle dipole sensor and asymmetric semicircle dipole sensor characteristics, the symmetric semicircle dipole sensor’s coupling property is better than that of asymmetric semicircle dipole sensor. At the same time, by changing the symmetric semicircle dipole transducer radius, the position of the feeder pole , the height of the feeder pole, analyze its influence on sensor features.

A Wideband Multimode Permeable Conformal Antenna Thinner Than <formula formulatype="inline"> <tex Notation="TeX">$\lambda /75$</tex> </formula> Using Advanced Ferromagnetic Laminate Composite Materials

A conformal permeable toroidal antenna operating in both a vertically polarized monopole mode and circularly polarized (CP) dipole mode in the UHF frequency range is designed based on theory of magneto-dielectric radiators. This antenna has been fabricated using a new advanced ferromagnetic laminate composite material whose high impedance and anisotropic properties enable an antenna that radiates via magnetic currents. The antenna, less than 0.5 m in diameter and less than 2 cm thick, was fabricated and tested. Including the imperfections of the feed network and a simple matching scheme, the antenna operates from 200 to 500 MHz with an input match of better than -10 dB, CP dipole realized gain as high as +2 dBi, and monopole mode vertically polarized gain as high as -1 dBi.

Electromagnetic properties of water on GHz frequencies for medicine tasks and metamaterial applications

In problems of modern radio physics and medicine it is important to know dielectric permittivity of liquids. Dispersion characteristics of water in UHF frequency band can be used to analyze the states of biological objects, and also to construct materials (metamanerials). The present work is intended to study the material properties of water in UHF frequency band based on two different techniques: Nicolson-Ross-Weir (NRW) [1] and the Active Nearfield Diagnostics [2].

Ray tracing propagation modeling for future small-cell and indoor applications: A review of current techniques

Applied for the first time to mobile radio propagation modeling at the beginning of the nineties, ray tracing is now living a second youth. It is probably the best model to assist in the design and planning of future short-range, millimeter-wave wireless systems, where the more limited propagation environment with respect to UHF frequencies allows to overcome traditional high-CPU time limitations while the higher operating frequency makes ray-optics approximations less drastic and allows to achieve an unprecedented level of accuracy. An overview of ray tracing propagation modeling is given in this paper, with a special attention to future prospects and applications. In particular, frontiers of ray-based propagation modeling such as extension to diffuse scattering, multidimensional channel characterization, multiple-input multiple-output (MIMO) capacity assessments, and future applications such as real-time ray tracing are addressed in the paper with reference to the work recently carried out at the University of Bologna.

Application of HFCT and UHF sensors in on-line partial discharge measurements for insulation diagnosis of high voltage equipment.

Partial discharge (PD) measurements provide valuable information for assessing the condition of high voltage (HV) insulation systems, contributing to their quality assurance. Different PD measuring techniques have been developed in the last years specially designed to perform on-line measurements. Non-conventional PD methods operating in high frequency bands are usually used when this type of tests are carried out. In PD measurements the signal acquisition, the subsequent signal processing and the capability to obtain an accurate diagnosis are conditioned by the selection of a suitable detection technique and by the implementation of effective signal processing tools. This paper proposes an optimized electromagnetic detection method based on the combined use of wideband PD sensors for measurements performed in the HF and UHF frequency ranges, together with the implementation of powerful processing tools. The effectiveness of the measuring techniques proposed is demonstrated through an example, where several PD sources are measured simultaneously in a HV installation consisting of a cable system connected by a plug-in terminal to a gas insulated substation (GIS) compartment.

Robot communication link using 802.11n or 900 MHz OFDM

Robots are increasingly being used in settings deemed too hazardous for humans. The communications link used in conjunction with these robots poses unique challenges, particularly in streaming video, which requires high bandwidth, typically found above 900MHz. In the reported literature, use of UHF below 2GHz for wireless operation on a robot platform is scarce, especially for non-line-of-sight (NLOS) applications and in addressing the feasibility of transmitting images or video. Furthermore, due to its superior ability to eliminate multipath-induced intersymbol interference (ISI), orthogonal frequency division multiplexing (OFDM) is considered to be the best waveform available today for wireless local area network (WLAN) applications. The documented use of OFDM combined with UHF below 2GHz is also sparse in the current literature. The objective of the research reported here is to demonstrate the performance of OFDM waveforms on a robot platform at two different UHF frequencies (900MHz and 2.4GHz).

UHF digital TV broadcasting and WRC-2015

Abstract Broadcasters deliver their products and services over the radio waves reaching millions of viewers and listeners. Until recently, frequency spectrum for broadcasting services, more so for UHF TV broadcasting, was easily available. But now mobile communication services, among many others, have laid claims on the UHF frequency bands. Preparations are underway globally to find appropriate solutions since the two services cannot share the same spectrum in a compatible manner. The World Radiocommunication Conference 2015 will take up the possible allocation of the UHF TV band for mobile communication. Expectations are that the decisions of the conference will have an adverse impact on TV broadcasting in the UHF frequency bands.

Field measurements for practical unlicensed communication in the UHF band

This paper presents the result of a measurement campaign conducted in Italy, Spain, and Romania to obtain empirical values for the parameters upon which unlicensed devices could distinguish in a hidden node scenario between empty and occupied TV channels. Signal power measurements in the UHF frequency band (470---860 MHz) have been carried out on rural, sub-urban, and urban sites, at different heights over the ground by using different analysis bandwidths. The results have been analyzed with respect to the hidden node margin problem, spectrum sensing bandwidth, and occupancy threshold, to produce a set of practical parameters upon which harmless unlicensed communication in the UHF TV bands is feasible.

Micromachined Coreless Single-Layer Transformer Without Crossovers

This letter presents the design and characterization of a novel micromachined fractal-shaped microtransformer for VHF and UHF frequency ranges. To eliminate the loss in magnetic core materials at high frequency and to achieve high coupling and quality factor, the microtransformer is designed to be coreless (air core). The novel design with a single metal layer and no crossover interconnections facilitates the standard metal multiuser microelectromechanical systems (metal-MUMPs®) fabrication process, as well as eliminates the interconnection resistance and electromagnetic interference due to vias and crossovers. A primary inductance of $\text{7.14}\; \text{nH}$ and a transformer quality factor of 5.92 were achieved at $\text{500}\; \text{MHz}$ . The coupling coefficient of the transformer at $\text{1}\; \text{GHz}$ is 0.77, and the efficiency of the transformer at $\text{250}\; \text{MHz}$ with matched load is 71%.

Growth and activity inhibition of yeast culture Saccharomyces cerevisiae by using microwave electromagnetic radiation

The influence of EMR UHF growth of yeast cell culture S. serevisiae . Established EMR UHF frequency band near 50–90 GHz radiation which leads to inhibition of cell growth of yeast. The research found that the effects of EMR frequency of 60 GHz, the duration of exposure 5–15 minutes and subsequent incubation in thermostat for 24 hours resulted in a decrease in the number of colonies by 50–60 %.

Beam steering patch antenna using reactive loading and Yagi‐antenna concept

ABSTRACTThis letter reports a technique to create beam‐steering antennas using reactive loading and passive patches. In this antenna configuration, the center patch is fed by a microstrip line and the two neighbor patches are excited through the mutual coupling from the active antenna. These two patches are loaded with a varactor diode and present a phase shift that depends on varactor capacitance. The impact of the mutual coupling on the impedance matching is investigated through a numerical calculation that combines 3D full‐wave simulation and network analysis formulas. The steering capability is enhanced by adding “director” passive patches as in the Yagi antenna principle. A prototype is designed, fabricated, and measured at UHF frequency (865–868 MHz) and shows a good agreement with the simulation. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:417–421, 2015

3-D Printing of Elements in Frequency Selective Arrays

3-D printing is a technology that enables the fabrication of complex objects directly from a digital model. Folding the elements of Frequency Selective arrays in three dimensions gives a significant reduction in the resonant frequency for a given cell dimension, and such structures are candidates for additive manufacture. The aim in this paper is to demonstrate by example the development of novel electromagnetic structures that could be fabricated in parallel and integral with the additive manufacture of buildings, for electromagnetic architecture control. The principle is illustrated with two new geometries based on dipole and loop elements. The cores of these structures were fabricated with a 3-D printer that uses a plaster-based material. Theoretical and experimental results confirm the operation of the surfaces within the UHF frequency band.

WhiteLAN

To build large and scalable setups, researchers usually employ mixed testbeds of regular SDR devices and cheaper, generally less flexible COTS devices. Such hybrid setups often face uncontrollable interference from other users in the ISM bands, which leads to incomparable results and requires frequent repetitions of experiments. Maintaining the ability to use COTS devices and ISM band-only SDR devices while moving experiments to less crowded frequency bands is thus of high interest to practical wireless communications research. In this paper we present whiteLAN, a frequency converter that enables IEEE 802.11b/g devices to operate over UHF frequencies. We discuss the advantages of a ISM-UHF converter setup, present the hardware architecture of our solution, and provide key performance metrics of the physical implementation. Through a comparative study of ISM vs. UHF operations we show that whiteLAN is viable for use as a plug-and-play extension for wireless research deployments.

High-Efficiency Wideband Rectifier for Single-Chip Batteryless Active Millimeter-Wave Identification (MMID) Tag in 65-nm Bulk CMOS Technology

This paper presents the development and demonstration of a high-efficiency rectifier for millimeter-wave-to-dc energy conversion. It is a critical circuit block that renders possible the use of a single CMOS chip die with no substrate and wiring, as the implementation of a batteryless, yet active tag for next-generation high data-rate millimeter-wave identification technologies. We also propose an architecture of a reader-tag system that addresses the underlying technical challenges. The rectifier is based on a differential drive cross-coupled topology that has been shown to work at UHF frequencies only so far. In this paper, we investigate significant challenges in implementing this topology at millimeter-wave frequencies with good power conversion efficiency (PCE). The analyses, design, and results presented in this work demonstrate the feasibility of achieving this by minimizing simultaneously the small on-resistance and the reverse leakage current in the MOS transistors, and by reducing losses and parasitic capacitances through proper transistor sizing and layout optimization. Using a standard 65-nm bulk CMOS process, a chip was designed, fabricated, and tested under different input and output loading conditions. The rectifier exhibits an overall PCE of 20% at 24 GHz, 18% at 35 GHz, and 11% at 60 GHz under RF available driving power of 6, 6, and 3 dBm, respectively, and output load resistance of 1, 1, and 2 kΩ, respectively. These PCE performances at millimeter-wave frequencies have never been reported in the literature.

Magnetic aspect sensitivity of high‐latitude E region irregularities measured by the RAX‐2 CubeSat

The second Radio Aurora Explorer (RAX‐2) satellite has completed more than 30 conjunction experiments with the Advanced Modular Incoherent Scatter Radar chain of incoherent scatter radars in Alaska and Resolute Bay, Canada. Coherent radar echoing occurred during four of the passes: three when E region electron drifts exceeded the ion acoustic speed threshold and one during HF heating of the ionosphere by the High Frequency Active Auroral Research Program heater. In this paper, we present the results for the first three passes associated with backscatter from natural irregularities. We analyze, in detail, the largest drift case because the plasma turbulence was the most intense and because the corresponding ground‐to‐space bistatic scattering geometry was the most favorable for magnetic aspect sensitivity analysis. A set of data analysis procedures including interference removal, autocorrelation analysis, and the application of a radar beam deconvolution algorithm mapped the distribution of E region backscatter with 3 km resolution in altitude and ∼0.1° in magnetic aspect angle. To our knowledge, these are the highest resolution altitude‐resolved magnetic aspect sensitivity measurements made at UHF frequencies in the auroral region. In this paper, we show that despite the large electron drift speed of ∼1500 m/s, the magnetic aspect sensitivity of submeter scale irregularities is much higher than previously reported. The root‐mean‐square of the aspect angle distribution varied monotonically between 0.5° and 0.1° for the altitude range 100–110 km. Findings from this single but compelling event suggest that submeter scale waves propagating at larger angles from the main E×B flow direction (secondary waves) have parallel electric fields that are too small to contribute to E region electron heating. It is possible that anomalous electron heating in the auroral electrojet can be explained by (a) the dynamics of those submeter scale waves propagating in the E×B direction (primary waves) or (b) the dynamics of longer wavelengths.

Dual Polarized Reconfigurable Frequency Selective Surfaces

Novel band-stop active frequency selective surfaces (FSS) capable of modifying their response for different polarizations are proposed. Geometries based on full rings, and split rings are employed. The designs using full rings are able to tune over a wide frequency range while designs using split rings tune in a narrow frequency band. Both structures use a new biasing methodology which allows independent control of rows and columns of FSS arrays, therefore permitting independent modification of the transmission responses at the vertical and horizontal polarizations. Convoluting the shape of the elements significantly reduces the sensitivity to angle of wave incidence. The aim is to demonstrate a technology that could be used for various applications including modification of the electromagnetic architecture of buildings and the control of electromagnetic wave propagation to improve the efficiency of radio spectrum use. The surfaces incorporate commercially available, low cost, varactor diodes and surface mount resistors. Theoretical and experimental results confirm the operation of the surfaces within the UHF frequency band.

Illustration of the Impedance Behaviour of Extremely Low-Profile Coupled Shorted-Patches Antennas for UHF RFID of People

The recently introduced coupled shorted-patches technique for the design of extremely low-profile UHF RFID tag antennas is used to illustrate the flexibility of selected feeding methods for tuning the antenna input impedance for the complex values required for matching with typical RFID chips. We present parametric studies of the impedance behaviour of dipole-excited and directly excited antennas designed for radiofrequency identification of people in the European UHF frequency band. Our study can significantly facilitate the design of this class of on-body tag antennas.