Reverberation Chamber Measurements Research Articles

Base-Case Model for Measurement Uncertainty in a Reverberation Chamber Including Frequency Stirring

We address the uncertainty of reverberation chamber (RC) measurements in presence of both mechanical and frequency stirring (FS). A base-case model is derived for reverberation fields affected by the measurement uncertainty due to the lack of a perfect statistical uniformity of fields in a RC. It is found that the measurement uncertainty associated with the FS depends on both the total uncorrelated samples and the local insertion loss (IL). The local IL depends on the frequency stirring bandwidth (FSB). The model allows us for obtaining separate measurement uncertainty contributions. Measurements support the achieved uncertainty model. In particular, results show that the dependence on the IL is normally rather weak also when very wide FSBs are used.

Design and Calibration of a mm-Wave Personal Exposure Meter for 5G Exposure Assessment in Indoor Diffuse Environments

For the first time, a mm-wave personal exposure meter (mm-PEM) for the 5th generation of mobile networks (5G) exposure assessment in indoor diffuse fields is presented. The design is based on simulations and on-phantom calibration measurements in a mm-wave reverberation chamber (RC) at 60 GHz. The mm-PEM consists of an array of nine antennas on the body. Using the mm-PEM, the incident power density (IPD) is measured in the unloaded RC, for the antenna(s) on the phantom and RC loaded with phantom. The uncertainty of the mm-PEM is then determined in terms of its response, which is defined as the ratio of antenna aperture for the above measurement scenarios. Using nine antennas, the designed meter has a response of 1.043 (0.17 dB) at 60 GHz, which is very close to 1 (0 dB), the desired ideal response value. The mm-PEM measured an IPD of 96.6 W m− 2 at 60 GHz in the RC, for an input power of 1 W. In addition, the average absorption cross-section of the phantom is determined as 225 cm2, which is an excellent agreement with its physical dimensions.

Notice of Retraction: Analysis of Near-Field Shielding Effectiveness for the SiP Module

In this letter, near-field scanning technology is utilized to analyze the shielding effectiveness (SE) of the system-in-package (SiP) module at the frequency of 1–6 GHz. Different definitions of the near-field SE are explored and analyzed. The SE is defined by using values of the radiated magnetic near-field from the SiP module, including the maximum value, the spatial averaged value, and the value at the same observation point, respectively. The SE defined by the spatial averaged value is a reasonable method to represent the overall SE of a well-shielded SiP module especially at low frequencies. Besides, a comparison of the SE between the reverberation chamber measurement and averaged magnetic near field is carried on. Good consistency is obtained, which confirms the reliability and efficiency of the near-field scanning method.

A Novel Method for Calculating the Radiated Disturbance From Pantograph Arcing in High-Speed Railway

Pantograph arcing is a key electromagnetic disturbance source to affect train control system in high-speed railway. Since the characteristics of pantograph arcing are related to train speed, it is necessary to investigate effective numerical modeling and measurement method. However, due to the uncontrollable train speed during onsite measurement, it is difficult to study the radiated disturbance from arcing in the corresponding speed and repeat the same measurement. Therefore, a method that combines numerical modeling and reverberation chamber measurements for calculating the radiated disturbance from pantograph arcing in a high-speed railway is proposed. Numerical models of train and sensitive equipment are built to calculate the coupling coefficient in CONCEPT II. And a new measurement procedure in reverberation chamber using pulse signal as the reference source is proposed based on a speed-controllable laboratory replica to measure the total radiated power of pantograph arcing. Then, the radiated disturbance from pantograph arcing to the sensitive equipment is achieved with the coupling coefficient and the total radiated power of arcing. The method is verified by laboratory experiments. This method can solve the uncontrollable train speed problem during on-site measurement and improve the repeatability of measurement.

Antenna Measurements in Reverberation Chamber Using USRP

This paper shows that a universal software radio peripheral (USRP) can be used to measure the complete passive over-the-air (OTA) performance of multiport antennas for multiple-input multiple-output (MIMO) systems. The passive MIMO OTA measurements are performed in a reverberation chamber using the USRP as a measurement instrument. The total embedded radiation efficiencies, the correlation, and the resulting diversity gain are extracted from transmission measurements only. These are in good agreement with S-parameter measurements (both transmission and reflection) obtained with a vector network analyzer (VNA). The proposed measurement approach involving USRPs provide an economical alternative to these type of measurements as compared to high-end equipment.

Verification of the Rician K ‐factor‐based uncertainty model for measurements in reverberation chambers

Measurements in reverberation chamber (RC) produce data that are random, and therefore they need to be processed from the statistical point-of-view for obtaining the desired characteristics and the accuracy. The complex channel transfer function in the RC follows complex Gaussian distribution provided that the RC is well stirred. The authors have recently presented a new uncertainty model based on the presence of an unstirred component of the transfer function, which was modelled by introducing an average Rician K-factor. The model was validated in two RCs with translating mode-stirring plates, being able to correctly describe the improvement in accuracy by rotating the antenna under test, and by blocking the line-of-sight between this and the fixed RC antenna(s). In the present study, they apply this uncertainty model to four RCs with different settings (e.g. RC volumes, number of plates or fixed RC antennas, translating and rotating mode-stirrers etc.). For each RC, they examine the measurement uncertainty under different loading conditions. To repeat (during the different measurements) the actual mode-stirrer positions at which the transfer function is sampled, they conduct all the measurements with stepwise (instead of continuous) mode-stirring. The model is shown to work well for all the cases.

Proximity‐effect test for lossy wireless‐device measurements in reverberation chambers

The authors present a test method for quantifying and reducing systematic errors arising from antenna proximity to lossy objects in over-the-air performance testing of lossy large-form-factor wireless devices. The method determines the extent to which antenna proximity to lossy, large-form-factor objects influences the measured reference power transfer function. The test may be used to pre-characterise a given chamber set-up in terms of a minimum distance between antennas and lossy objects. They illustrate the use of the method in a total radiated power measurement of a large, commercially available, machine-to-machine device, where agreement to anechoic-chamber measurements is demonstrated to within the measurement uncertainty.

UHF RFID tags backscattered power measurement in reverberation chamber

Presented is a methodology for measuring the power backscattered by ultra-high frequency radio frequency identification (UHF RFID) tags by using a modes stirrer reverberation chamber. The actual measurement methodology is described and its advantage and disadvantage against the conventional setup using anechoic chambers are outlined. Then, some results of power measurements performed with the three Gen2 class 1 tags are presented. The experimented tags' sensitivity and radiation efficiency as a function of incident power are finally derived. The results are very encouraging and demonstrate the feasibility of such a characterisation in modes stirred reverberation chambers. All the measurements were carried out at a single frequency of about 866 MHz.

Interpreting the Total Isotropic Sensitivity and Diversity Gain of LTE-Enabled Wireless Devices From Over-the-Air Throughput Measurements in Reverberation Chambers

The characterization of the performance of wireless devices is key to developing new RF products conforming to the latest communications protocols. Traditionally, communication performance tests have focused on the RF performance of the tested devices, e.g., smart phones, pads, laptops, and so on. In particular, the focus has shifted from conducted (i.e., cabled) measurements to more realistic over-the-air (OTA) characterization of the RF performance of these devices in transmit or receive mode. For example, the receiver performance of 2G and 3G wireless devices can be measured in terms of the total isotropic sensitivity (TIS) that depends on the antenna and the receiver parts of a wireless device. These measurements can be performed in a reverberation chamber setup. However, standard TIS measurements can be time-consuming and do not reflect the actual performance gains of multiple-input multiple-output antenna systems operating over orthogonal frequency division multiplexing channels, such as those encountered in 4G long-term evolution (LTE) systems. Therefore, in order to meet both time and cost efficiency requirements, we propose here a new method to determine the TIS, as well as the diversity performance, of an LTE device based on throughput measurements. The proposed method shows that the TIS of an LTE device is characterized much faster directly from OTA throughput measurements than from standard TIS measurements and with excellent accuracy.

Antenna Gain and Radiation Pattern Measurements in Reverberation Chamber Using Doppler Effect

In a recent paper, a novel technique that allows for the first time to perform actual antenna radiation pattern measurements in reverberation chamber (RC) has been presented. Even though its results were in good agreement with the ones obtained in anechoic chamber (AC), it was necessary to repeat stationary measurements locating the antenna under test (AUT) at N different fixed positions along its line-of-sight to a fixed probe antenna per angle under study, thus multiplying by N the measurement time when compared to measuring in AC. On the contrary, in this contribution, an improvement of this technique is presented, obtaining an antenna radiation pattern by performing only one measurement per angle under study, taking advantage of real-time Doppler effect. Moreover, the antenna gain is obtained from only one of these measurements, without the need to know the antenna efficiency, by using the Friis transmission equation. In order to demonstrate the validity of this improved technique, the radiation pattern for both E- and H- planes and the gain of a horn antenna have been measured in an RC, being the results in good agreement with the ones obtained in AC and the values provided by the antenna manufacturer, respectively.

Improved MIMO Throughput With Inverse Power Allocation—Study Using USRP Measurement in Reverberation Chamber

In this letter, we study the spatial multiplexing throughputs of multiple-input-multiple-output (MIMO) systems with fixed modulation and coding scheme (i.e., fixed peak rate) based on measurement of the universal software radio peripheral (USRP) in a reverberation chamber. In particular, we propose a simple inverse power allocation scheme for the singular value decomposition (SVD)-based MIMO system. Using the proposed power allocation, the power saving (for achieving the same throughput), compared to the SVD-MIMO without power allocation, is about 2.5 dB. Good agreement is observed between the USRP measurement and the simulation.

Uncertainty From Choice of Mode-Stirring Technique in Reverberation-Chamber Measurements

We develop methods for assessing the component of measurement uncertainty arising from various combinations of mode-stirring techniques in reverberation-chamber measurements. We first develop a components-of-variance model that describes this component of uncertainty in terms of physical mechanisms related to the chamber. We illustrate the use of the model in conjunction with measurements to identify the optimal mode-stirring sequence for a measurement of received power.

Broadband Measurement of Absorption Cross Section of the Human Body in a Reverberation Chamber

We present broadband reverberation chamber measurements of the absorption cross section (ACS) of the human body averaged over all directions of incidence and angles of polarization. This frequency-dependent parameter characterizes the interactions between the body and the enclosures of reverberant environments such as aircraft cabins, and is, therefore, important for the determination of the overall Q-factor and, hence, the field strength illuminating equipment inside such enclosures. It also correlates directly with the electromagnetic exposure of occupants of reverberant environments. The average ACS of nine subjects was measured at frequencies over the range 1-8.5 GHz. For a 75-kg male, the ACS varied between 0.18 and 0.45 square meters over this range. ACS also correlated with body surface area for the subjects tested. The results agree well with computational electromagnetic simulations, but are obtained much more rapidly. We have used the obtained values of ACS to estimate the effect of passengers on the Q-factor of a typical airliner cabin.

Experimental Investigation of the Number of Independent Samples and the Measurement Uncertainty in a Reverberation Chamber

Due to the complicated and time-varying boundary conditions, reverberation chamber (RC) measurements are usually studied using statistical analysis. Hence, it is of importance to know the number of independent samples of the measurements. Different methods for estimating the number of independent samples has been proposed in the literature. This paper uses the spatial degrees of freedom method to estimate the independent sample number. Comparing with the commonly used autocorrelation function method, the proposed method requires less computation time and provides a smaller estimation bias for correlated samples and a smaller estimation variance once above a certain sample number. The estimated independent sample number can be used to explain the dependences of the measurement uncertainty on frequency, mode stirrers, and RC loading. Finally, the estimated independent sample number is used to predict the standard deviation (STD) of the average power level for different loading configurations, where good agreements are observed.

Spatial Autocovariances of Scattering Parameters Measured in a Lossy Reverberation Chamber

We derive a statistical model for the spatial autocovariance of two-port scattering parameters measured in a high-loss reverberation chamber for single-mode antennas. The theoretical model accounts for first-order antenna-antenna and antenna- environment interactions arising from scattering off the measurement antennas. The model is shown to provide a good description of the empirical spatial autocovariances calculated from measurements of scattering parameters in a reverberation chamber for different loading configurations. This provides new insight into the complex antenna-antenna and antenna-environment interactions that occur in reverberation chamber measurements. Additional applications include reducing the correlation between reverberation chamber measurements obtained with position stirring and measuring the orientation-averaged total scattering cross section of arbitrary structures.

MRC Diversity and MIMO Capacity Evaluations of Multi-Port Antennas Using Reverberation Chamber and Anechoic Chamber

It has been shown that diversity gains and MIMO capacity of multi-port antennas can be conveniently determined from reverberation chamber measurements. In this paper, we first present the covariance eigenvalue approach and the embedded far field function method to determine diversity gain and MIMO capacity, respectively, for arbitrary multi-port antennas. Then, we discuss the convergence of the covariance eigenvalue approach. In the end, we apply both methods to compare MRC diversity gains and MIMO capacity measured in a reverberation chamber (based on direct channel measurements) and an anechoic chamber (based on measurements of the embedded far field functions and efficiencies at all antenna ports). The comparison is performed over 2-8 GHz using a wideband multi-port antenna in two configurations. There are in general good agreements between the reverberation and anechoic chamber measurement results.

On Independent Platform Sample Number for Reverberation Chamber Measurements

The turn-table platform stirring technique is used to improve the measurement accuracy of a reverberation chamber (RC). It is usually assumed that the half-wavelength platform spatial sampling results in independent samples, which can be used to approximate the independent platform sample number. But the approximation is rather coarse. This paper presents a measurement-based method to determine the independent platform sample number. This method is simple and accurate. In contrast to the half-wavelength coarse approximation that depends only on frequency, this method in addition illustrates the dependence of the independent platform sample number on RC loading and mode stirring.

Reverberation Chamber Measurement Correlation

This contribution evaluates the utility of several different metrics for studying correlation between reverberation chamber measurements collected at different stirrer positions. Metrics considered are the autocovariance, the correlation matrix, and two metrics based upon the entropy of the data correlation matrix: 1) the effective number of uncorrelated measurements and 2) the measurement efficiency. The different metrics are shown to be useful for different correlation analyses. Application of these metrics reveals that the correlation between reverberation chamber measurements is strongly affected by stirring methodology, loading configuration, and measurement frequency.

Effects of edge screens on the absorption of blocks of theatre chairs

This paper reports new measurement results investigating the use of screens around samples of theatre chairs to minimize edge effects when measuring theatre chair absorption in reverberation chambers. The absorption measurements included both full scale and scale model measurements in reverberation chambers and a model recital hall. The use of screens has been proposed to better approximate the sound absorption of the larger blocks of chairs in auditoria. The method of measuring the absorption of blocks of chairs with screens around their edges and located in the corner of a reverberation chamber did not give results indicative of the values obtained for larger areas in auditoria. The addition of screens around samples of chairs did not eliminate the variation of absorption coefficients with perimeter/area ratio. The results of extrapolations from measurements of blocks of screened chairs to infinite samples gave lower absorption coefficients than found for blocks of unscreened chairs. The absorption of chairs in large performance halls can best be predicted using the P/A method to extrapolate from reverberation chamber measurements of smaller samples of unscreened chairs, with a range of P/A values, to the larger samples and lower P/A ratios of blocks of chairs typical of performance spaces.

Energy-based measurements in reverberation chambers

Standardized reverberation chamber measurements, including those of absorption coefficients, scattering coefficients, and sound power, rely on the acquisition and processing of squared acoustic pressure (or potential energy density) from many sound field locations. Kinetic energy density, total energy density, and the newly defined generalized energy density exhibit greater spatial uniformity in enclosed fields (especially at lower frequencies), which makes them more favorable quantities for these measurements. They produce greater accuracy or require fewer source-receiver positions to produce acceptable levels of accuracy. This paper explores their use and provides several analytical and experimental results to demonstrate their benefits.