Wideband Measurements Research Articles

A novel scheme for global scattering center modeling of radar targets

A novel scheme for extracting the global scattering center model of radar targets is proposed in this paper. The 2D/3D scattering center models can be reconstructed based on the wideband measurements at different viewing angles. The sphere spreading of the 1D scattering center projections is exploited. The 1D-2D/3D scatterer map (OTSM) is designed to manifest the high dimensional scattering characteristic of radar targets. The Hough transform and the least squares method are used to extract the stable scattering centers and their scattering coefficients. This modeling method does not need a high density of the spatial grid, which greatly cuts down the necessary original data. The model built in this way describes the stable point scattering mechanisms in a large spatial extent and can be extrapolated to other frequencies in the optical region. Examples verify the validity of both the model and the method.

Wide-band measurement of complex permittivity using an overmoded circular cavity

A large terminating circular cavity structure is proposed in this paper for measuring the complex permittivity of low-loss dielectric materials over a very wide frequency range of 20–100 GHz. Compared to many other widely used configurations employing off-resonant circular cavity, this new overmoded circular cavity provides higher precision of relative permittivity results and a wider frequency range. Extensive measurements are carried out and measured results for two sample materials are presented. An inverse algorithm using the mode-matching method is introduced to calculate the complex permittivity of the dielectric sample. An error analysis is also presented to estimate the errors incurred due to the uncertainty in the S-parameter measurement, sample size, location of the coupling probe.

A micromachined stationary lamellar grating interferometer for Fourier transform spectroscopy

This paper reports a novel micromachined stationary lamellar grating interferometer for Fourier transform (FT) based spectroscopy applications. The interferometer employs a set of tilted interdigitated light reflecting beams to produce an interferogram with spatially varying optical path difference (OPD) recorded by a line photodetector array. Due to the advantages including robustness and the absence of mechanical moving parts and optical beam splitters, the proposed spectrometer may be built in a relatively small volume and with moderate cost for wide-band radiation spectra measurement, fast time-resolved spectroscopy and for field use. The proposed stationary lamellar grating FT spectrometer was implemented using a silicon-on-insulator (SOI) micromachining process. The prototype spectrometer demonstrated a full width at half maximum (FWHM) spectral resolution of 2 nm at a wavelength of 532 nm and of 2.6 nm at 632.8 nm.

Wideband Measures of Middle-Ear Functioning

Wideband Measures of Middle-Ear Functioning

Local orbital frame predictor for LEO drag-free satellite

This paper is concerned with on-board real-time position and rate prediction of the spacecraft centre-of-mass as input data to local orbital frame (LORF) determination for Low-Earth Orbit drag-free satellites. Study and simulation results are justified by Drag-Free and Attitude Control of the GOCE satellite (Gravity field and steady-state Ocean Circulation Explorer), the LORF being the instantaneous reference for satellite attitude and scientific data. The paper focuses on modeling issues to obtain an accurate orbit dynamics at lower frequencies for reducing integration error because of the narrow-band filter requested by the assumed wide-band measurement errors. A further remedy in this sense is the addition of a second order disturbance dynamics leaving unexplained bounded noise components. Simulated results are presented with reference to GOCE mission.

A Digital Directional Coupler With Applications to Partial Discharge Measurements

This paper presents a digital directional coupler (DDC) that separates forward- and backward-traveling waves on a transmission line. Based on two independent wideband measurements of voltage and current and on frequency-domain digital wave splitting using a fast Fourier transform (FFT), the DDC is a versatile device for direction separation. A practical procedure is described for the calibration of the digital processor with respect to the particular transmission line and the voltage and current sensors that are being used. As an experiment, a DDC was designed and implemented using low-cost wideband sensors and was installed with medium-voltage equipment in a power distribution station. Partial discharge (PD) measurements were conducted on cross-linked polyethylene (XLPE)-insulated power cables to illustrate the directional separation capabilities of the DDC.

Test of far-infrared atmospheric spectroscopy using wide-band balloon-borne measurements of the upwelling radiance

The spectroscopy of the constituents of the Earth's atmosphere that are active in the far infrared spectral region, among which the water vapour is the main one, has been validated through the analysis of wide-band nadir-looking spectra acquired with the Radiation Explorer in the Far Infrared—Prototype for Applications and Development (REFIR-PAD) Fourier transform spectroradiometer. The spectra, covering from 100 to 1400 cm - 1 with a 0.475 cm - 1 unapodized resolution, were acquired during a balloon flight performed in a tropical region in 2005. Atmospheric variables, namely water vapour and temperature vertical profiles, were retrieved from the REFIR-PAD data, and the residuals of the fitting are here critically analysed for the search of systematic effects that can be ascribed to spectroscopic errors. In the spectral interval between 150 and 600 cm - 1 nosignificant inconsistency is detected between the residuals and the measurement uncertainty, proving the good quality of the radiative transfer model and of the HITRAN 2004 spectroscopic database. Significant difference are instead observed when the HITRAN 2000 database is used.

Exploiting multiple-input multiple-output in the personal sphere

An analysis of the propagation characteristics of communication links in the personal sphere is presented. The results of two wideband measurement campaigns in the 5.2 GHz band involving on-body multiple-input multiple-output (MIMO) arrays are reported. In the first measurement, transmission takes place between on-body antennas and a uniform linear array, positioned at close range and with line-of-sight (LOS) propagation conditions. Despite the LOS operation, MIMO is shown to offer a significant increase in the information theoretic capacity of the system when compared with a conventional single-input single-output (SISO) antenna system. Although this appears counter-intuitive to the well-known fact that uncorrelated scattering results in high capacity, two previously less well-known mechanisms are highlighted to explain this result. This analysis reveals the potential use of MIMO in personal area networks. The second measurement campaign uses two on-body MIMO arrays to focus on the subject of body area network propagation. Analysis of the SISO characteristics of the links highlights the influence of the user on the channel. Body shadowing and user motion are shown to lead to multiple rapid changes in the channel characteristics. Again, MIMO is shown to be able to offer performance enhancement. In the measured channels, polarisation diversity is shown to outperform spatial diversity.

60-GHz Wideband Radio Channel Sounder

This paper describes a developed wideband millimeter-wave radio channel sounder, which is based on the previously developed 2- and 5-GHz channel-sounder concept. Performance is analyzed, and examples of measurements, analysis, and comparison to lower frequencies are given. The sounder enables wideband (3-dB bandwidth of 100 MHz) measurements with continuous phase and excellent link budged without a cable connection between the transmitter and the receiver.

Analysis of Time of Arrival Estimation Using Wideband Measurements of Indoor Radio Propagations

Using time of arrival (TOA) to determine the distance between the transmitter and the receiver is the most popular technique for accurate indoor positioning. The accuracy of measuring the distance using this method is sensitive to the bandwidth of the system and the multipath condition between the wireless terminal and the access point. In general, as the bandwidth increases beyond a certain value, it is expected that the measured TOA error approaches zero. However, for the so-called undetected direct path (UDP) conditions, the system exhibits substantially high distance measurement errors that cannot be eliminated with the increase in the bandwidth of the system. In this paper, we provide an analysis of the behavior of superresolution and traditional TOA estimation algorithms in line-of-sight (LOS), non-LOS, and UDP conditions in indoor areas. The analysis is based on wideband frequency- domain measurements of the indoor radio channel propagations in several indoor areas, with special attention to the UDP conditions.

Analysis of charge transport during lightning using balloon‐borne electric field sensors and Lightning Mapping Array

Recently, wide band measurements of the electric field near a lightning flash have been obtained by a balloon‐borne electric field sonde or Esonde. This paper develops new techniques for analyzing lightning‐associated charge transport in a thundercloud by using both the Esonde data and simultaneous Lightning Mapping Array (LMA) measurements of VHF pulses emitted during lightning breakdown processes. Innovations in this paper include the following: (1) A filtering procedure is developed to separate the background field associated with instrument rotation and cloud charging processes from the lightning‐induced electric field change. Because of the abrupt change in the signal caused by lightning, standard filtering techniques do not apply. A new mathematical procedure is developed to estimate the background electric field that would have existed if the lightning had not occurred. The estimated background field is subtracted from the measured field to obtain the lightning‐induced field change. (2) Techniques are developed to estimate the charge transport due to lightning. At any instant of time during a cloud‐to‐ground (CG) flash, we estimate the charge transport by a monopole. During an intracloud (IC) flash, we estimate the charge transport by a dipole. Since the location of the monopole and dipole changes with time, they are referred to as a dynamic monopole and a dynamic dipole. The following physical constraints are used to achieve a unique fit: charge conservation during an IC flash, separation (distance between the CG monopole charge center and the ground and separation between IC dipole charge centers both exceed a minimum threshold), location (charge is placed on lightning channel), and likelihood (after a statistical analysis based on instrument uncertainty, highly unlikely charge locations are excluded). To implement the constraint that the charge is located on the lightning channel, we develop a mathematical object called the “pulse graph.” Vertices in the graph are pulse locations obtained from the Lightning Mapping Array. Edges in the graph (that is, the pairs of vertices which are connected by line segments) are obtained by joining, in a systematic way, neighboring vertices. One CG and two IC flashes observed on 18 August 2004 near Langmuir Laboratory are analyzed. In the CG flash, initial strokes drained 12 C charge from an altitude of 5 km, while an intermediate stroke discharged 12 C from a higher charge center at 8 km. For the IC flashes, the current flow lagged behind the channel formation by time intervals on the order of 0.1 s, roughly the same time delay observed for lightning optical signals detected by NASA's Lightning Imaging Sensor.

Thermochromic liquid crystal temperature measurements through a borescope imaging system

Thermochromic liquid crystals (TLCs) have proven to be a valuable tool for the collection of full-field, high-resolution heat transfer data. This paper presents an extension of previously developed calibration techniques to a simplified transonic linear cascade for a highly cambered turbine blade geometry. This required the introduction of miniature periscopes to image the measurement surfaces. The procedures and equipment used to ensure high-accuracy wide-band TLC measurements are presented. These included a geometry-matched calibration device, mechanisms to accurately position the borescope imaging optics, an algorithm to automatically divide the imaging region into a large number of calibration subregions (termed as cells), and algorithms to correct for geometric and optical image distortions. The cell calibration approach is shown to halve calibration times and dramatically reduce memory requirements when compared to a pixel-by-pixel calibration. The results of an extensive validation study are presented.

Empirical pathloss model for indoor geolocation using UWB measurements

A novel empirical approach is presented for modelling the path loss behaviour of the direct path (DP) between the transmitter and receiver, which is important for time-of-arrival-based indoor geolocation coverage characterisation. Using ultra wideband (UWB) measurements in four sites and three ranging scenarios, pathloss models at 500 MHz and 3 GHz system bandwidths are provided, centred on 4.5 GHz for DP and total signal power. In addition, ranging coverage analysis is provided using the DP models.

A Wideband Spatial Channel Model for System-Wide Simulations

A wideband space-time channel model is defined, which captures the multiple dependencies and variability in multicell system-wide operating environments. The model provides a unified treatment of spatial and temporal parameters, giving their statistical description and dependencies across a large geographical area for three outdoor environments pertinent to third-generation cellular system simulations. Parameter values are drawn from a broad base of recently published wideband and multiple-antenna measurements. A methodology is given to generate fast-fading coefficients between a base station and a mobile user based on the summation of directional plane waves derived from the statistics of the space-time parameters. Extensions to the baseline channel model, such as polarized antennas, are given to provide a greater variety of spatial environments. Despite its comprehensive nature, the model's implementation complexity is reasonable so it can be used in simulating large-scale systems. Output statistics and capacities are used to illustrate the main characteristics of the model

LOCAL ORBITAL FRAME OBSERVER FOR LEO DRAG-FREE SATELLITES

This paper is concerned with on-board real-time CoM position and rate determination as input data to local orbital frame (LORF) for Low-Earth Orbit drag-free satellites. Study and simulation results are justified by Drag-Free and Attitude Control of the GOCE satellite (Gravity field and steady-state Ocean Circulation Explorer), the LORF being the reference for satellite attitude and scientific data. The paper focuses on modelling issues to obtain accurate orbit dynamics at lower frequencies for reducing integration error, because of the narrow-band filter requested by wide-band measurement errors. A further remedy in this sense is the addition of a second-order disturbance dynamics bounding unexplained noise components. Simulated results are presented with reference to GOCE mission.

Channel Characterization of Indoor Wireless Personal Area Networks

The wireless channel for nomadic diversity-based wireless networks operating at 1.9 GHz is characterized. Using a 1 times 2 wideband measurement chain, four typical indoor office and industrial environments have been investigated: a corridor, an office room, a laboratory room and a large industrial hall. The measurement equipment is constituted by an 80-MHz transmitter. At the receiver, two omnidirectional antennas are connected to a wideband channel sounder through a switch, in order to measure an estimate of the instantaneous vector channel. Special attention is given to the experimental procedure itself, so as to take into account the specificity of nomadic systems (as opposed to usual mobile systems). The measurement analysis reveals that the shadowing, Rician K-factor and delay-spread are lognormally distributed. A path-loss model is derived, and cross-correlations between K-factor, delay-spread and shadowing are analyzed. The channel correlations at the user terminal or at the access point are also derived, and related to the individual channel characteristics

Rapidly moving sources of upper band ELF/VLF chorus near the magnetic equator

Multiple simultaneous wideband (Gurnett et al., 2001) measurements on the Cluster spacecraft of upper band chorus emissions near the magnetic equator (at magnetic latitudes between −20° and 10° and L shells ranging between L = 4 and L = 5) are used to deduce the properties of the compact source regions of ELF/VLF chorus emissions. The frequency differences exhibited by the same chorus emissions observed on different spacecraft are interpreted (Inan et al., 2004) in terms of a differential Doppler shift, using a simple model involving rapidly moving sources traveling at speeds comparable to the parallel resonant velocity of counter‐streaming gyroresonant electrons. Cluster observations are used to determine the location and extent along the Earth's magnetic field lines of the source of chorus. Frequency and time differences between spacecraft are interpreted as a direct consequence of the rapid motion of highly localized source regions of chorus. In this paper, we examine the previously presented model of rapid motion of sources of chorus, extending the calculations to a three‐dimensional space, using measurements of the four Cluster spacecraft. These calculations of source location and velocity as a function of frequency indicate that chorus sources move a distance of ∼6000 km along the field lines. The emitted chorus waves at the source are assumed to have a wide range of wave normal angles, but the rays reaching the spacecraft seem to be the ones with lower angles (with some exceptions). The ranges of velocity obtained vary with frequency around values ranging from ∼0.01c to ∼0.04c.

Broadband channel measurement and analysis

An outdoor propagation measurement campaign for beyond 3G (B3G) as well as a wide-band indoor measurement campaign have been performed recently in Beijing, China, in which the sounding signals are transmitted by an one-antenna base station and received by a two-antenna mobile receiver operated at 3.49 ∼ 3.51 GHz bandwidth. Different scenarios: stationary line-of-sight (LoS), stationary non-LoS (NLoS) scenarios, and dynamic NLoS are deliberately chosen in a classic urban environment and office environment The initial results are presented in this article. Parameters including vector channel impulse response, path loss, rays number, excess delay spread etc. are extracted, analyzed, and briefly reported here.

Wideband measurement of the dielectric constant of an FR4 substrate using a parallel-coupled microstrip resonator

We have made a wideband measurement of the real part of the dielectric constant of flame retardant #4 epoxy (FR4), a common high-frequency printed-circuit-board insulator. We designed a novel test circuit, an electrically long parallel-coupled microstrip resonator, which was etched on a 0.014-in FR4 substrate, manufactured by NELCO, Melville, NY. We used a computer model of the resonator to extract the dielectric constant at the frequencies of zeroes in its measured transmission response. By adjusting the model's dielectric constant, we tuned the frequency of each zero to match the measured frequency, yielding the dielectric constant at that frequency. To validate our method and results, we present a simple, but original proof that the frequencies of zeroes in the resonator's transmission response are insensitive to input and output mismatches. Additionally, we compare the measured and predicted response of a two-stub filter designed with our measured data. The fabricated filter's measured return loss and insertion loss from 3 to 12 GHz are within 1% of the predictions of Agilent Technology's Momentum.

Wideband measurement of shear induced birefringence by quadrupole method

We developed a new method for the measurement of the dynamic birefringence induced by the alternating shear deformation in fluid samples. A quadrupole piezoactuator generates the pure shear deformation in the frequency range from 1Hzto5kHz and causes the molecular orientation, or the anisotropic conformation of polymers and molecular associations, which is observed by the optical ellipsometry technique. The spectrum of the shear-induced birefringence observed for the isotropic phase of the liquid crystal p-n-hexyl p′-cyanobiphenyl (6CB) shows linear dependence on the frequency up to 5kHz, corroborating the effective band of the experimental system. The sensitivity of the system was demonstrated by the quantitative measurement of the birefringence for the isotropic phase of p-n-pentyl p′-cyanobiphenyl (5CB). The system was also applied to the aqueous solution of the worm such as micelles and the result shows the relaxation of shear induced birefringence at around 10Hz, which agrees well with the previous reports.