Search

Abstract This paper proposes a new method for improving the partial discharge (PD) localization accuracy by detecting the best places of ultra‐high frequency (UHF) sensors on the power transformer tank. In this way, firstly, the critical sites inside the power transformer that can produce PD are determined. Then the sensors’ positioning is done in such a way that if the PD happens at each point of these critical sites, the distance between the estimated PD location obtained by solving the time difference of arrival (TDOA) equations and the actual PD location is laid in an acceptable range. For this purpose, the TDOA equations are linearized around the critical PD coordinates as a matrix form A.X = B. The configuration of the sensor positions that minimizes the condition number of the matrix A is the best configuration. To evaluate the effectiveness of the proposed method, several simulations and evaluations are performed on a power transformer in the CST software. The obtained results and comparing them with the previous method and also conventional arbitrary sensors positioning confirm the effectiveness of this method.

This paper proposes a new method for improving the partial discharge (PD) localization accuracy by detecting the best places of ultra‐high frequency (UHF) sensors on the power transformer tank. In this way, firstly, the critical sites inside the power transformer that can produce PD are determined. Then the sensors' positioning is done in such a way that if the PD happens at each point of these critical sites, the distance between the estimated PD location obtained by solving the time difference of arrival (TDOA) equations and the actual PD location is laid in an acceptable range. For this purpose, the TDOA equations are linearized around the critical PD coordinates as a matrix form A.X = B. The configuration of the sensor positions that minimizes the condition number of the matrix A is the best configuration. To evaluate the effectiveness of the proposed method, several simulations and evaluations are performed on a power transformer in the CST software. The obtained results and comparing them with the previous method and also conventional arbitrary sensors positioning confirm the effectiveness of this method. [ABSTRACT FROM AUTHOR]

To achieve comprehensive insulation deterioration motoring of power equipment and early fault warning in air-insulated substations, a data-driven partial discharge (PD) source localisation method employing noisy ultra-high frequency (UHF) received signal strength indicator (RSSI) and particle filter is proposed in this study. Compared with the existing UHF time-difference-based techniques, UHF wireless sensor arrays and RSSI-based methods provide an economical and high-adaptability solution. However, owing to the multi-pathing and shadowing effects, UHF signal attenuation cannot be modelled. Therefore, a Kalman filter was employed to smoothen the RSSI signal. Furthermore, a semi-parametric regression model is proposed to achieve a more accurate relationship between the RSSI and the transmission distance. Finally, in contrast to traditional localisation algorithms directly based on the RSSI ranging model, a particle filter was used to achieve higher accuracy. It predicted the best distribution of the position of PD by learning and considering all the system states of the previous moment. The laboratory test was performed within an area of 6 m × 6 m, and the results demonstrate that the mean PD source localisation error was 1.16 m, which gives a potential application for the identification of power equipment with insulation deterioration in a substation, while the accuracy is still needed to be verified further by field tests.

In this study, to improve the sensitivity and accuracy of the detection of surface partial discharge (PD) in gas insulation switchgears (GISs), a combination of ultra-high frequency (UHF) and optical methods is proposed based on an integrated sensor. The PD triggered by a fixed metal needle defect attached to the spacer is detected from PD inception to flashover in a real GIS. The characteristics of UHF and optical signals under different applied voltages are compared and analysed in terms of PD waveform, Phase Resolved Partial Discharge (PRPD) pattern, PD count and amplitude. The results show that the surface discharge process can be precisely divided into three stages according to the combined characteristics of the UHF and optical signals. The comparison of the two detection methods shows that the optical method can detect the weak avalanche PD under low voltage while UHF cannot, so it can detect more PDs than UHF method in an AC cycle. In addition, with the deterioration of solid insulation material, the amplitude of the optical signal increases significantly while the amplitude of the UHF signal only increases slightly. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that fluoronitrile (FN) Novec™ 4710 and fluoroketone (FK) Novec™ 5110 show higher dielectric strength than SF 6. These gases can be mixed with a buffer gas such as CO 2 and technical air to have suitable dielectric properties for high voltage insulation applications. With the rapid growth of HVDC networks, these gases may replace SF 6 in future HVDC apparatus such as GIS/GIL. This paper focuses on the study of the partial discharge (PD) characteristics of SF 6 and SF6 alternative gases with a protrusion defect on the high voltage conductor with DC voltage. The results show that, for calculated equivalent SF 6 dielectric strength under homogeneous electric field, a difference in terms of partial discharge inception voltage was noted for gas mixtures compared to SF 6. This difference may be due to the influence of gas pressure under highly inhomogeneous electric field. FN-CO 2 and FK-Air mixtures showed the highest PD amplitude under positive polarity while it was higher under negative polarity for SF 6. Moreover, PD repetition frequency is higher for SF 6 investigated alternative gases. The results can help for the design of SF 6 free HVDC GIS partial discharge monitoring system. [ABSTRACT FROM AUTHOR]

• Proposing a novel idea to generate acoustic phase-resolved partial discharge patterns. • Describing the theory behind the presented idea. • Comparing the acoustic and electrical PRPDs of five different configurations. • Giving details of the sensors, their conditioning circuit, and functioning principles. Detection of partial discharges (PD) is of great importance in the monitoring of high voltage devices and their early fault diagnosis. The ultrasonic sensing is one of the PD detection methods proposed in the literature. Normally, the partial discharge signals are mapped onto the voltage waveform to generate the phase resolved partial discharge or PRPD patterns for the fault type recognition. However, the travel time of ultrasonic signals hinders using a similar process in the ultrasonic PD method. In order to avoid this problem and to improve the ultrasonic PD detection by generating corresponding PRPD, this paper presents a novel method that utilizes ultra-high frequency (UHF) and ultrasonic signals of PD, simultaneously. To show the performance of this method, a circuit is built for ultrasonic PD detection first. In the next step, a wideband antenna is utilized, and its signals are compared with the ultrasonic sensor output to compensate for the PD travel time error. Finally, the PRPD patterns are generated and analyzed for five different configurations. The electrical PRPDs are measured for these cases and compared with the acoustic ones. The experimental results demonstrated in this paper prove the potential of the proposed idea to generate acoustic PRPD for the purpose of PD type recognition. [ABSTRACT FROM AUTHOR]

This study presents preliminary results on the signature of a large offshore wind turbine collected using an active S-band radar. The intensity fluctuations of this clutter signal in the range and Doppler domain are characterised, looking at their evolution over time, statistics, and spread in the Doppler domain. The polarisation impact on the signatures is also discussed.

Detection of corona discharge of the transmission line can reflect its health status and provide warning information for maintenance. Some existing detection methods are flawed and cannot be used widely. This study presents a new method by measuring the electromagnetic wave caused by corona discharge with RF antenna. Then a circularly polarised log-periodic antenna was designed by making two pairs of log-periodic antennas 90° orthogonal. Finally, this antenna was simulated and manufactured to detect electromagnetic signals, the result shows that the time domain signal of corona discharge is a high frequency oscillation wave and its fast Fourier transform main distributes between 200 and 350 MHz.

This study presents preliminary results on the signature of a large offshore wind turbine collected using an active S-band radar. The intensity fluctuations of this clutter signal in the range and Doppler domain are characterised, looking at their evolution over time, statistics, and spread in the Doppler domain. The polarisation impact on the signatures is also discussed. [ABSTRACT FROM AUTHOR]

Detection of corona discharge of the transmission line can reflect its health status and provide warning information for maintenance. Some existing detection methods are flawed and cannot be used widely. This study presents a new method by measuring the electromagnetic wave caused by corona discharge with RF antenna. Then a circularly polarised log-periodic antenna was designed by making two pairs of log-periodic antennas 90° orthogonal. Finally, this antenna was simulated and manufactured to detect electromagnetic signals, the result shows that the time domain signal of corona discharge is a high frequency oscillation wave and its fast Fourier transform main distributes between 200 and 350 MHz. [ABSTRACT FROM AUTHOR]

UHF (ultra high frequency) method has been widely used in PD (partial discharge) detection for its high sensitivity. The resonance, distortion, and attenuation appearing in the propagation process of UHF signals in GIS (gas insulated switchgear) will influence the real situation of PD detection. Therefore, it is necessary to investigate the effect of GIS components such as disconnectors or high voltage conductors on the propagation characteristics of PD-induced UHF signals in various voltage classes GIS. The factors of PD signals propagation characteristics in axial and radial directions are both analysed to avoid the effect caused by placement of sensor in this paper. First, the simulation models of GIS are built based on FDTD (finite difference time domain) method. Then the propagation characteristics of PD-induced UHF signals are studied in the GIS with different disconnector gap lengths and different high voltage conductor radii. Finally, the reliability of the simulation results is verified by compared with laboratory tests. The disconnector gap and the change of conductor radii can both result in the signals attenuation which rises highest in the direction of 180°. The lower the GIS class voltage is, the larger the attenuation of signals after passing through disconnector gap is.

This Letter proposes the application of RF technology for the non-destructive detection of spoiled coconut at the pre-processing stage. Since the dielectric property of coconut water changes at different stages of coconut, the sensor measures the content of water inside a coconut sample non-destructively at 2.45 GHz. The sensor has been trained to determine the threshold water level between healthy and spoiled coconut which in turn can be used to sort the coconuts. The measurement results have been presented for different processing stages of coconut for different samples. Detecting coconut quality through dielectric sensing reveals some very impressive results and opens the doors for better consumption. [ABSTRACT FROM AUTHOR]

An original partial discharge generated in oil insulation identification methodology based on simultaneously conducted measurements using electrical method, ultra high frequency method and acoustic emission method is presented in the paper. Three different partial discharge model sources as well as measuring instruments commonly applied for partial discharge detection in electrical power transformers are yielded within a laboratory research. Total of 45 scenarios, including proposed spark gap configurations, selected supply voltage levels and UHF frequencies are analyzed during measurements series. Furthermore, form among total of 93 descriptors assigned for every applied partial discharge model source configuration there are 24 proposed as potentially useful for partial discharge identification applications with their 95% confidence bounds. Attempt of discriminative descriptors selection for partial discharge source analysis in on-site transformer applications as well as a proposal of unique descriptors according to every selected spark gap configuration that could be potentially useful for partial discharge identification purposes are the main purpose of the presented paper. The proposed methodology verification on a real life transformer with particular consideration of the selected descriptors potential utility in the fields of partial discharge detection and identification in electrical power industry applications confirmed a proposed methodology usefulness. [ABSTRACT FROM AUTHOR]

Copyright of Maintenance & Reliability / Eksploatacja i Niezawodność is the property of Polish Scientific & Technical Society Consumables, Polish Maintenance Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A novel phase‐locked loop (PLL) architecture including a composite phase frequency detector (PFD), two charge pumps, variable loop filter topology and voltage‐controlled oscillator is proposed in this study. Composite PFD offers higher‐gain and loop bandwidth (BW) during tracking when Δϕ>π and provides a lower‐gain and loop BW during tracking when Δϕ<π as well as after lock‐in. The PLL system is designed to ensure stability by maximising and equalising phase margin in both the linear as well as non‐linear operations. The transfer characteristics of composite PFD are free from the blind zone and also found possible to eliminate glitches from the output. A prototype of PLL operating at 2.56 GHz developed on 180 nm complementary metal–oxide–semiconductor process is found to achieve reference spur of −71.4 dBc, lock time of 2.05 μs, peak‐to‐peak jitter of 3.412 ps, phase noise of −110 dBc/Hz at 100 kHz and final placement area of 0.244mm2. [ABSTRACT FROM AUTHOR]

The ultra‐high‐frequency (UHF) method is efficient in partial discharges (PDs) detection in gas‐insulated switchgear (GIS). The features extraction of UHF signals is significant for propagation characteristics analysis and PD pattern classification. The PD‐induced UHF signals are acquired by the internal UHF sensors in an actual 252 kV L‐shaped GIS. The short‐time Fourier transform method is applied to process UHF signals and describe the propagation characteristics in L‐shaped GIS. Hu's invariant moments of energy density distribution are extracted as features in time–frequency plane. The features are utilised to discriminate different PD defect patterns in actual GIS model by the support vector machine classifier and achieve good results. Finally, a novel system of features extraction and classification of UHF signals is summarised. [ABSTRACT FROM AUTHOR]

In many cases of on-site PD measurement, it is difficult to acquire the perfect phase angle of the PD signal synchronized with the applied voltage. This paper describes a new method of PD diagnosis which can classify the types of defects for unknown phase-shifted PDs using decision tree method. 327 cases of on-site PD data were collected in the field. 5 valid parameters were extracted and the decision tree-based diagnostic algorithm was used to classify types of 6 PDs and 4 noises clearly. Finally we confirmed the new method of PD diagnosis can be applied to on-site GIS diagnosis. [ABSTRACT FROM AUTHOR]

Ultra‐high frequency (UHF) technique is chosen for partial discharge (PD) detection due to its excellent anti‐interference and stability. The existing UHF PD localisation methods are mainly based on time‐difference technique, that suffer high hardware cost due to the high sampling rate requirement. The wireless UHF sensors together with the scene analysis methods, i.e. received signal strength indicator (RSSI) fingerprint, provide us a low hardware cost and high environmental adaptability solution for PD localisation in substation. The proposed PD localisation method here is divided into two stages. In the offline stage, the RSSI fingerprint map is established by site survey. In the online stage, the position of PD source is estimated by a probabilistic approach. To reduce the influence of noise, the RSSI fingerprints are transformed to a low‐dimensional subspace, while the most of redundant noise is discarded. Furthermore, the PD heterogeneity and interference in the offline stage are also discussed and solved by normalisation and clustering algorithm, respectively. A filed test is performed and the results indicate that the mean localisation error is 1.87 m and 82.6% localisation errors are <3 m. The workload in the offline stage is also reduced ∼50%. [ABSTRACT FROM AUTHOR]

In this study, a novel ultra‐high frequency (UHF) sensor using an inner grading electrode inside an insulting spacer is employed to detect gas‐insulated switchgear (GIS) partial discharge (PD[AQ ID=Q1]). The simulation of the waveguide modes of the 252 kV GIS and the frequency response characteristics of this UHF sensor are performed by using the finite difference time domain (FDTD) method. Three kinds of typical defects are employed to investigate the PD detection characteristics of this UHF sensor. It is shown that the resonance frequencies of this sensor are extremely abundant below 3 GHz, and the major resonance frequencies around 0.5–1.2 and 2.2–3 GHz. The phase‐resolved PD (PRPD) images accumulated by using this UHF sensor present the typical PRPD images of defects. The main frequency spectrum of the metal protrusion on a high‐voltage conductor and floating potential defects are distributed below 1.5 GHz, which is consistent with waveguide mode simulation. A resonance frequency of a grading electrode UHF sensor appears at about 115 MHz, which is close to the simulation value of a resonance frequency at 140 MHz. The PD detection sensitivity of this sensor is much higher than that of an external sensor; however, it is a little lower than that of an internal sensor. [ABSTRACT FROM AUTHOR]

This paper proposes an optimal placement model of ultra-high frequency (UHF) sensors for accurate location of partial discharge (PD) in gas-insulated switchgear (GIS). The model is based on 0-1 program in consideration of the attenuation influence on the propagation of electromagnetic (EM) waves generated by PD in GIS. the optimal placement plan improves the economy, observability, and accuracy of PD locating. After synchronously acquiring the time of the initial EM waves reaching each UHF sensor, PD occurring time can be obtained. Then, initial locating results can be acquired by using the Euclidean distance measuring method and the extended time difference of arriving (TDOA) location method. With the information of all UHF sensors and the inherent topological structure of GIS, the locating accuracy can be further improved. The method is verified by experiment, showing that the method can avoid the influence of false information and obtain higher locating accuracy by revising initial locating results.

Microwave‐based measurement can provide new methods and practical solutions for the challenging task of measurement inside large industrial combustion chambers. In order to measure or communicate inside a combustion chamber using microwaves, the spectrum of background noise at microwave frequencies must be known. This study investigates the basic electromagnetic spectrum in flames, concentrating on microwave frequencies from 0.1 to 19 GHz. The study introduces, as reference values, known results from forest flames and flames in controlled environments. The focus of the work is the level of background noise at microwave frequencies and the impact of this noise on radio communication inside the combustion chamber. The effects of the microwave radiation levels are compared with the requirements of practical communication systems such as Bluetooth and narrowband ISM (industrial, scientific, medical) systems at 800–950 MHz. [ABSTRACT FROM AUTHOR]

In this study, a substrate integrated waveguide (SIW) combined with complementary split‐ring resonator (CSRR) structure is proposed for high‐sensitivity measurement of complex permittivity of low loss material at 2.45 GHz. The simulated results demonstrated that the small changes can be sensed through loading the CSRR structure on both sides of SIW. Then, the experiments are performed on various dielectric samples to validate the proposed structure by measuring the particulate samples with different moisture contents and solution samples in different mixed volume ratio. The measured results show that the sensitivity of the proposed SIW with CSRR structure is always higher than the structure without CSRR. Furthermore, neural network based on actual experimental scattering parameters is used for obtaining the permittivity of samples under test. The experimental values agree well with the theoretical values, and the relative errors of ε′ and ε′′ are <5 and 10%. [ABSTRACT FROM AUTHOR]

The reliability of electrical energy networks depends on both, the quality and reliability of its electrical equipment, e.g. power transformers. Local failures inside their insulation may lead to breakdowns and hence to high outage and penalty costs. Power transformers can be tested on partial discharge (PD) activity before commissioning and monitored during service in order to prevent these events. In the first part, this contribution presents different types of ultra-high frequency (UHF) sensors for PD measurement. Various applications of UHF sensors and proper sensor installation are discussed. The second part of the contribution is about the necessity of UHF measurement comparability and reproducibility. Therefore, a new calibration procedure for the UHF method is proposed and discussed in respect of the procedure for the IEC 60270 compliant conventional electric method. The characterization of UHF sensors is a key precondition for the UHF calibration process in order to obtain calibration for the full measurement path. Sensor characteristics are described by the antenna factor (AF) which is determined under inside transformer conditions in an oil-filled Gigahertz Transversal Electromagnetic cell (GTEM cell). In addition to the calibration procedure, the performance of the installed sensor has to be determined. The evaluation is based on the concept of transmitting electromagnetic waves through the transformer tank from one UHF sensor to another. This performance check procedure is used in this contribution for the examination of the influence of the sensor's insertion depth into the tank. These results are compared to the reference GTEM cell measurement used for calibration. [ABSTRACT FROM AUTHOR]

Gas insulated switchgear (GIS) is used in power system more and more widely. With the increased voltage level of power system, field impulse voltage withstand test becomes increasingly important. It would be beneficial for a comprehensive insulation evaluation to carry out the detection of partial discharge (PD) under impulse voltage withstand test in field. Metal protrusions or particles on HV conductor are typical defects in GIS and are critical at lightning impulse voltages. This paper therefore aims at PD characteristics study on needle-plane defect under oscillating lightning impulse (OLI). PD detection system was established based on ultra-high frequency (UHF) and pulse current detection. Then, the PD of a needle-plane defect under negative OLI was measured. The relation between statistical time lag, PD amplitude, PD times and the applied voltage was analyzed respectively based on UHF detection. The results show that UHF detection has high sensitivity and it is suitable in field impulse voltage withstand test. PDs occur around each wave peak of the applied voltage. With the increase of peak voltage, PD magnitude and PD times in each oscillation cycle both increase linearly. Further analysis indicates that the occurrence and development of PD under negative OLI can be interpreted by electron emission from metal surface, field detachment from negative ions and corona stabilization effect. This approach is valuable for PD measurement and analysis in field impulse voltage withstand test for GIS. [ABSTRACT FROM AUTHOR]

A method is presented to improve the determination of the rotational velocity of an on‐axis spinning object. It uses the Orbital Angular Momentum (OAM) of an electromagnetic wave at 2.47 GHz, and measures the rotational Doppler frequency shift of a reflected wave. From this shift, the rotational velocity and the direction of rotation can be directly estimated with very good accuracy. [ABSTRACT FROM AUTHOR]

Ultra‐high‐frequency (UHF) method is regarded as an effective approach for partial discharge (PD) detection in gas insulated substation (GIS). The feature parameters representing UHF signal characteristics can be extracted from its waveform, and applied to PD source classification and mixed signals separation. In this study, an UHF signal feature extraction algorithm based on cumulative energy (CE) technique is proposed. The CE functions in time domain (TCE) and frequency domain (FCE) are calculated from UHF waveforms and their fast Fourier transform spectrums, respectively. The mathematical morphology gradient (MMG) operation is applied to TCE and FCE to characterise their rising behavior. The feature parameters including width, area and sharpness are extracted from CEs and MMGs in both time and frequency domain. Moreover, the extracted features are applied to UHF signals classification and mixed signals separation. First, experiments on four kinds of typical defects in a 252 kV GIS are performed, and the classification performance of the extracted features is examined with the acquired signals. Second, by clustering the extracted features with fuzzy maximum‐likelihood algorithm, mixed UHF signals originated from multiple PD sources are successfully separated. The results indicate that the proposed features are effective for representing UHF signal characteristics. [ABSTRACT FROM AUTHOR]

Common reasons for local failures in power transformers are partial discharges (PD) in the electric insulation. The ultra-high frequency (UHF) PD measurement method gained in importance for transformer diagnosis and monitoring within the last years. Due to its robustness against external noise, it is suitable for both, factory acceptance tests (FAT) and site acceptance tests (SAT). For the application at acceptance tests, it is necessary that the UHF technique is a reliable testing method and also comparable between different UHF measurement systems. Therefore, the UHF sensor's characteristic has to be included in a calibration procedure by using its antenna factor (AF). This contribution implements a custom-built oil-filled Gigahertz-Transversal-Electromagnetic cell (GTEM cell) for the AF evaluation. In the first part, the GTEM cell's design and dimensioning are illustrated and the cell is evaluated in terms of its high frequency behavior. The second part determines the AF of two different UHF sensor types: UHF Drain Valve Sensors and UHF Plate Sensors using the GTEM cell. Additionally, the influences of insertion depths and standardized gate valves on the Drain Valve Sensor's AF are taken into account. [ABSTRACT FROM PUBLISHER]

This paper describes work done recently to characterize and better understand propagation of PD signals in the VHF and UHF bands in GIS. While carrying out a routine CIGRE TF 15/33.03.05 UHF PD Sensitivity Verification Step 1 Laboratory Test procedure, RF transmission measurements were made on the same GIS set-up employed for the CIGRE test, using an RF vector network analyzer. In addition, a comprehensive 3-D RF field simulation model of the set-up was created, based on the detailed design drawings of the GIS. The transmission measurements were simulated in the RF model and the results compared with the actual measurement data. This shows once again the extreme complexity of GIS as an RF signal propagation environment, the difficulty describing a transfer function or in extracting useful meaning from such measurements, set against the relative simplicity of the CIGRE procedure for establishing measurement sensitivity and guidelines for sensor placement. [ABSTRACT FROM PUBLISHER]

The paper, prepared by CIGRE WG D1.25, presents the experience in practical application of sensitivity verification of the UHF partial discharge detection system for GIS after its introduction by ELECTRA Report in 1999. A detailed description of the two-step procedure, Step 1 in laboratory and Step 2 on-site, is given and supported by examples. Guidelines will help manufacturers and users in the effective application of the UHF method for PD detection on GIS and will permit to avoid technical misinterpretations. The procedure is described in details in CIGRE Technical Brochure. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

A fast detection system based on a terahertz quantum‐well photodetector (QWP) and a fast modulated terahertz quantum‐cascade laser is presented. Response waveforms and eye diagrams under different modulation frequencies are acquired. Employing the current measurement system without any high speed optimisation obtains the highest response rate of 0.5 GHz. The experiment demonstrates that the QWP is potentially useful for fast detection and high speed communication applications. [ABSTRACT FROM AUTHOR]

Abstract: We examine the potential for expansion of the white space spectrum sharing model in the 400MHz band. As opposed to UHF broadcast spectrum, which contains unassigned or idle segments known as white spaces, the 400MHz band is characterised by intensive licence usage. However, productive spectrum usage does not guarantee allocative efficiency, which would require knowledge of the highest value service for each licence. 400MHz frequencies are not priced on opportunity cost. It is therefore difficult to ascertain the economically efficient mix of services to deploy in the 400MHz band. Drawing parallels with the high-economic value revealed and generated through the operations of unlicensed white space devices in UHF broadcast spectrum, we identify untapped 400MHz spectrum capacity, which we refer to as narrowband spaces. Encouraging dynamic spectrum usage of narrowband spaces could, similarly to TV white space usage help realise the efficient allocation of the 400MHz band. However, the narrowband nature of the 400MHz licences and high licensing turnover imply a significantly different concept of dynamic spectrum access than that considered for TV Bands. The paper discusses regulatory implications and the type of services suited to exploit narrowband spaces. [Copyright &y& Elsevier]

ABSTRACT A single layer of equilateral triangular patch antenna is achieved, which operates at 870 MHz and 2.45 GHz suitable for UHF and microwave radio frequency identification application. By shaping the corners of triangular patch, the antenna excites the radiation modes of TM10 and TM21 and suppresses the unwanted TM20 mode to give boresight of directed radiation patterns. This also alters the excited surface distribution of the radiating patch to enhance the antenna gain. A good agreement is obtained between the simulated and experimental results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:69-72, 2014 [ABSTRACT FROM AUTHOR]

Highlights: [•] Spectrum measurements were taken for the UHF and GSM bands over a six week period. [•] An improved method for statistically determining spectrum occupancy was presented. [•] Occupancy in the UHF band was found to be fairly constant at approximately only 20%. [•] The GSM 900 and 1800MHz bands were found to be 92% and 40% occupied respectively. [•] In the GSM bands, occupancy fluctuated by up to 20% according to the time of day. [ABSTRACT FROM AUTHOR]

A rectangular corrugated horn antenna is designed for use as a probe for planar, cylindrical or spherical near-field measurements. The performance of the new design is compared with that of standard rectangular probes. The proposed probe has a nearly omnidirectional radiation pattern with very low cross polarization over a wide bandwidth. Moreover, the small size of the antenna is very suitable for use as a probe. Simulations and optimizations were carried out with a software tool based on the moment method. [ABSTRACT FROM PUBLISHER]

This paper presents comprehensive experimental results obtained from narrowband and wideband radio-channel measurements in an underground mine with narrow veins at 2.4 GHz. From continuous-wave (CW) measurement data, large-scale distance-power curves and path-loss exponents of the environment are determined. Other relevant parameters, such as the mean excess delay, the maximum excess delay, the root-mean-square (rms) delay spread, and the coherence bandwidth are extracted from the wideband-measurement data. Results show a propagation behavior that is specific for these underground environments with rough surfaces. The rms delay spread does not follow a dual-slope relation with respect to distance, as in environments with smooth surfaces. Moreover, the dependence of the rms delay spread on the bidimensional position of the user is found to be very significant. For the majority of locations, the rms delay-spread values are less than 60 ns. [ABSTRACT FROM PUBLISHER]

We are developing a multifrequency multistatic synthetic aperture radar (SAR) for determining polar ice sheet basal conditions. To obtain data for designing and optimizing radar performance, we performed field measurements with a network-analyzer-based system during the 2003 field season at the North Greenland Ice Core Project camp (75.1 N and 42.3 W). From the measurements, we determine the ice sheet complex transfer function over the frequency range from 110-500 MHz by deconvolving out the system transfer function. Over this frequency range, we observe an increase in total loss of 8±2.5 dB using a linear regression to the log-scale data. With the ice sheet transfer function and an ice extinction model, we estimate the return loss from the basal surface to be approximately 37 dB. These measurements have broad applicability to interpreting radar-sounding data, which are widely used in glaciological studies of the polar ice sheets. These data have also been used in the link budget for the design considerations of the multifrequency multistatic SAR system. [ABSTRACT FROM PUBLISHER]

This Letter presents a multi‐half‐loop wideband antenna operating over a ground plane. The proposed structure has a voltage standing wave ratio <2 in the frequency range of 0.95–12.5 GHz (171%). One important attribute of this antenna is robust power‐handling, combined with a super‐wide operating bandwidth. The structure's simplicity allows robustness and easily predictable radiation properties, beneficial for several measurement systems. The antenna can be easily optimised by 4NEC2 freeware. To manufacture the antenna, only the simple mechanical treatment of metal is necessary. [ABSTRACT FROM AUTHOR]

If the wave output by a voltage controlled oscillator (VCO) has the property of having no phase jump also when its frequency is swiftly changed, the measures of the phase before and after a fast frequency change can be used for calculating the time at which such event has occurred. Based on this property, a precise time measurement instrument has been designed and built. A non‐optimised version has better than 100ps resolution full width at half maximum, is VCO drift compensated and is able to time events against a stable clock running at 312.5MHz. The VCO frequency of the prototype jumps from 47 to 59MHz. The analogue hardware is fairly limited. Applications may range from particle timing to time resolved fluorescence spectroscopy to range finding through time‐of‐flight methods. [ABSTRACT FROM AUTHOR]

On-chip microstrip transmission lines have been measured on-wafer from below 1 GHz up to 110 GHz. Using different pad de-embedding techniques as well as a technique based on two transmission lines of different length, the characteristic transmission line parameters have been accurately determined. The results are compared against simulation results from an electromagnetic full-wave solution and the parametric IBM model which is available in the technology's design kit. [ABSTRACT FROM PUBLISHER]

A new technique for analyzing partial discharge (PD) signals based on ultra-high frequency (UHF) measurements is presented, using results from site tests. Signals from simultaneously active discharge sources can be mapped according to their point of origin in a manner that will simplify the interpretation of phase-resolved discharge patterns. The scheme has the potential to allow automated location and tracking of multiple discharge sources in power transformers and other metal-clad high-voltage plants. [ABSTRACT FROM PUBLISHER]

The use of a directional terminal antenna on a wireless link can enhance the received power by as much as the antenna gain. In local scattering, however, the enhancement will be smaller. We call this decrement the gain reduction factor, Δ. We present a statistical model of Δ for fixed suburban paths at 1.9 GHz, based on angle-of-arrival measurements in New Jersey. Our results address the influences of antenna height, antenna beamwidth, distance, and season [ABSTRACT FROM PUBLISHER]

We have developed a new permeance meter in the 1 MHz-1.5 GHz range using either a microstrip pickup coil or a shielded loop pickup coil. Both pickup coils and the driving plates are free from LC resonance due to impedance matching. In the MHz range we must consider signal-to-noise ratio of the pickup coil. In the GHz range we must eliminate the voltage induced by the electric field, and an electromagnetic higher order mode in the driving plates. [ABSTRACT FROM PUBLISHER]

A swept frequency method for measuring the magnetic permeability of thin films for frequencies up to 2 GHz with a resolution at 1 GHz of /spl sim/0.1 /spl mu/m in permeance is described. It is based on the measurement of impedance of a strip loop loaded with the sample under test. The method employs a commercial impedance or network analyzer, is simple, and suitable for permeability measurements of thin magnetic films which are used in recording heads and microwave components. [ABSTRACT FROM PUBLISHER]

This paper proposes an optimal placement model of ultra-high frequency (UHF) sensors for accurate location of partial discharge (PD) in gas-insulated switchgear (GIS). The model is based on 0-1 program in consideration of the attenuation influence on the propagation of electromagnetic (EM) waves generated by PD in GIS. the optimal placement plan improves the economy, observability, and accuracy of PD locating. After synchronously acquiring the time of the initial EM waves reaching each UHF sensor, PD occurring time can be obtained. Then, initial locating results can be acquired by using the Euclidean distance measuring method and the extended time difference of arriving (TDOA) location method. With the information of all UHF sensors and the inherent topological structure of GIS, the locating accuracy can be further improved. The method is verified by experiment, showing that the method can avoid the influence of false information and obtain higher locating accuracy by revising initial locating results. [ABSTRACT FROM AUTHOR]