Source Stirring Research Articles

Passive Antenna Characterization Through Impedance Correlations in a Diffuse Field

Ambient noise correlations allow the passive recovery of Green’s functions between two probes. Recently, the same approach has been applied to electromagnetism, but by correlating diffuse fields in mode-stirred chambers. Until now, only the correlation of S-parameters has been studied. However, it has very recently been shown that the result can be difficult to interpret. To overcome this limitation, a new approach is proposed in this article to directly estimate the self- and mutual impedances of two coupled antennas from impedance correlations. The theoretical developments presented are validated experimentally in a reverberation chamber (RC) excited by a single antenna where mechanical and source stirring techniques are combined to generate a sufficiently diffuse field environment. It is shown, with antennas of different properties, that this approach allows reconstructing with good accuracy the complex impedance matrix between two receiving antennas as well as the transmission coefficient between them. The extracted gain pattern, in good agreement with that measured in an anechoic chamber, shows the good sensitivity of the proposed passive characterization technique.

Emission Test Method for Source Stirred Reverberation Chambers With Scalar Measurements

This paper describes a novel method to reconstruct the radiated emission of a device under test placed in a reverberation chamber equipped with multiple monopole source stirring technique. The method is based on the measurement of the normal component of the electric field, collected close to the walls of the chamber by the monopole antennas. The main improvement from the previous formulation of the method is that the only knowledge of the amplitude of the electric field is sufficient to reconstruct, within a predictable range of uncertainty, the maximum level of the radiation of the device over all the directions at a given distance. The consequent advantage is that the method is immediately usable in a realistic scenario for emission tests, where an EMI receiver or a spectrum analyzer are used to measure the electric field and therefore only the amplitude of the field is retrieved.

Emulation of the Rician K-Factor of 5G Propagation in a Source Stirred Reverberation Chamber

This paper presents a novel algorithm to emulate the Rician K-factor of a wireless communication environment using a reverberation chamber. In particular, it was focused on the frequency bands used by 5G technology for data transmission. Unlike the current state of the art, the increase of the Rician K-factor is not achieved by inserting lossy material in the chamber, but through the proposed algorithm, which selects a subset of electromagnetic field realizations inside the chamber. The algorithm was first applied to the results of a simulation obtained by using an analytical model that predicts the main physical quantities inside a rectangular cavity where a multiple monopole source stirring action is implemented. Subsequently, the robustness of the algorithm and its applicability was tested on a set of data retrieved from experimental measurements. In all of the considered scenarios, the validity of the proposed method was demonstrated.

Biased Estimation of Antenna Radiation Efficiency Within Reverberation Chambers Due to Unstirred Field: Role of Antenna Stirring

Reverberation chambers (RCs) are now a reliable alternative to anechoic chambers to perform antenna radiation efficiency measurements. Most methods, including the two-antenna one used in this paper, are based on the evaluation of the stirred components of the scattering parameters. They are obtained by subtracting the average scattering parameters from the measured ones. This averaging is performed thanks to mechanical stirring, that is sometimes supplemented by additional stirring such as antenna stirring (which includes platform stirring and source stirring). In this paper, we present an extensive study on the role of antenna stirring in the retrieved radiation efficiency. Four measurement campaigns were successively performed: without antenna stirring, with platform stirring only, with source stirring only, and with a combined stirring of both antennas. Performing only source stirring or platform stirring leads to a biased estimation of the radiation efficiency. Therefore, we showed that the stirring of both antennas is mandatory in order to obtain an unbiased estimation of the radiation efficiency.

Improving the Reverberation Chamber Performance Using a Reconfigurable Source Stirring Antenna Array

An antenna array composed of 16 asymmetric distributed monopoles on a circular dielectric substrate is proposed to use as a reconfigurable source stirrer in a reverberation chamber (RC). The distance between antennas is above λ2 to ensure the isolation between antennas below −15 dB. In order to ensure the mutual independence of the stirring modes of the antenna array, the 16 monopoles are asymmetrically distributed on both sides with X and Y as axes. The stirring efficiency of a stirrer is related to its size, and usually a higher stirring efficiency means a larger stirrer. The source stirring technique can achieve high efficiency, but the rotation of a source stirring antenna is limited to the radius of the turntable in an RC. To solve this problem, we propose to use an antenna array as a reconfigurable source stirrer, which can achieve a high efficiency of source stirring. As the antenna array can achieve source stirring and mechanical stirring at the same time, the source stirring section is not limited to the radius of the turntable; the switch between the selected antennas of the antenna array can increase the actual stirring samples of the stirring. Thus, the efficiency can be improved significantly and has been verified by the measurement results. The volume occupied by the conventional mechanical stirrer is reduced, which improves the working volume. The figures of merit, such as the field uniformity (FU), the independent sample numbers, the average K-factor, and the total scattering cross-section (TSCS), are measured and compared to the conventional mechanical stirring, mechanical stirring, and source stirring of the antenna array. Measurement results of the reconfigurable stir are illustrated below. FU has the best convergence and the lowest value, below 0.5 dB. The independent sample number is the largest. K-factor is the lowest, and most ranges are below −15 dB. Additionally, the proposed method has the largest TSCS, above 2 m2. These confirm that the proposed reconfigurable source stirring technique outperforms other three stirring techniques significantly. The antenna array can be easy to disassemble and install in different RC. With a wide range of working band, the proposed method can be applied to 5G OTA testing.

Optimization of the Measurement Technique for Emissions in Reverberation Chamber Using the Equivalence Principle

This paper presents an optimization of a method to reconstruct the radiated emissions of an equipment under test by the measurement of the electric field samples collected on the walls of a reverberation chamber. This means that only the orthogonal component of the electric field is necessary to obtain the radiative behavior of the device in free space conditions. The use of the equivalence principle allows one to reduce the number of equivalent sources used to reconstruct the radiation of the device. In fact, in the previous version of the method, the sources are placed into the entirety of working volume of the reverberation chamber. In the current version of the method, only the surface surrounding the equipment under test is discretized. The analytical implementation of the method is proposed for a particular stirring action: the multiple monopole source stirring technique. This technique is based on an array of monopoles placed onto the walls of the cavity, and therefore no further hardware is needed for the reconstruction of the radiated emissions. The method is experimentally validated in a real scenario.

Improving Field Uniformity Using Source Stirring With Orbital Angular Momentum Modes in a Reverberation Chamber

The orbital angular momentum (OAM) offers new degrees of freedom and finds application in communications and radar imaging. In this letter, the OAM is introduced for reverberation chamber (RC) measurements using OAM metasurfaces. Because of the space limitation of the used RC, the OAM source has to be located near a sidewall, which inevitably causes some degradation of the OAM purity. Nevertheless, our experimental results show that the field uniformity of the RC can be improved effectively by using the OAM metasurfaces.

A Source Stirred Reverberation Chamber Using a Robotic Arm

In a reverberation chamber, the stirring efficiency of the source stir technique is very high. However, to apply the source stir, the configuration (position, orientation, or polarization) of the transmitting (Tx) antenna has to be changed every time in the stirring process. To solve this problem, we use a three-dimensional printed robotic arm to control the position and orientation of the Tx antenna; thus, the source stirring process can be performed automatically. The measurement results are validated and compared with that from mechanical stirrers. Figures of merit such as autocorrelation, average K -factor, and total scattering cross-section are presented. The statistical distribution is also verified by using Kolmogorov–Smirnov test. Results show that the source stir technique outperforms the mechanical stirring technique significantly.

Low-Frequency Theoretical Analysis of a Source-Stirred Reverberation Chamber

Theoretical analysis of a reverberation chamber excited through the source-stirring technique at low frequency is presented. A complete analytical solution returns quickly the electromagnetic field inside the chamber thanks to an efficient computation technique for the slowly convergent triple series. The stirring function is accomplished by 62 monopole antennas, irregularly distributed on the chamber walls, and subsequently, fed two at a time for a total of 1891 combinations. At first, the empty chamber is characterized, as usually it is done for any test site and then a receiving loop is considered in the chamber working volume to simulate a device under test (DUT) and the induced voltage is studied in terms of amplitude and phase. The analytical approach allows to account for all mutual couplings between transmitting antennas and the receiving structure through the computation of all self and mutual impedances. We demonstrate that the contribution of chamber irrotational modes cannot be neglected in the computation of both antenna input impedance and DUT-induced voltage. The present study highlights the capability of source stirring to change the field amplitude and orientation in the undermoded condition. This advantage takes also benefit from the use of an out-of-phase feeding for each pair of active antennas, achieving a higher DUT-induced voltage.

Probability Density Function of the Quality Factor for Reverberation Chambers Operating With Hybrid Stirring Including Frequency Stirring

In this letter, we deal with the probability density function (PDF) for the quality factor Q of reverberation chambers operating with combined mechanical and frequency stirring techniques. It will be shown the Q PDF of step-tuned and mode-stirred reverberation chambers (RCs), respectively, where the mechanical and frequency stirring are combined, and how it is affected by the width of the frequency sweep. The results for source-stirred RCs, where the frequency stirring is combined with source stirring, are implicitly obtained as well. By the results, possible effects on the measurements due to combinations of stirring techniques, including the frequency stirring, are also shown.

MODEL SELECTION FOR INVESTIGATION OF THE FIELD DISTRIBUTION IN A REVERBERATION CHAMBER

In this work two model selection criteria, i.e., Akaike's information criterion (AIC) and minimum description length (MDL), are applied to measurements in a RC with Rayleigh, Rician, Nakagami, Bessel K, and Weibull distributions as the distribution candidate set. In spite of small differences of the AIC and MDL tests (due to their different penalty terms on distribution parameters), both criteria result in similar conclusions. Results show that the Rayleigh distribution provides the overall good fit to the Cartesian field amplitude, especially for an overmoded RC, and that the Weibull distribution provides good fit to the Cartesian field amplitude in an undermoded or loaded RC. In addition, it is found that both the Rician and Weibull distributions provide improved approximations of the Cartesian field amplitude in a loaded RC with non-negligible unstirred components and that the transition from undermoded RC to overmoded RC depends not only on the operating frequency and mode-stirrer efficiency (as it is commonly believed) but also on source stirring and RC loading.

Design and Testing of an Antenna System for the Source Stirring Technique in Reverberation Chambers

The paper describes the design and testing of a radiating structure developed to reverberate electromagnetic fields in shielded chambers. The radiating system consists of a set of conical broadband wire antennas, adapted to cover the operational frequency range of 1 to 3GHz. Twenty antennas are used to build up the structure, and field stirring is achieved by switching on 190 different combinations that generate field statistics and field uniformity quite similar to those of a mechanically stirred reverberation chamber (RC). All the measurements prescribed by standard and literature were carried out to test the stirring capabilities of the radiating structure, and to assess that the RC field fulfills the IEC 61000-4-21 requirements.

A Theoretical Feasibility Study of a Source Stirring Reverberation Chamber

A novel theoretical feasibility study to reverberate a large metallic chamber is proposed. The method is based on the displacement of a radiating antenna inside the chamber, and the reverberating effect is obtained by coupling the antenna current in different ways with the cavity modes. This technique eliminates mechanical rotating paddles inside the chamber and offers the advantage of a continuous-wave operation compared with the frequency stirring method. The reverberating characteristics of the proposed technique are evaluated by calculating the field statistics. The analyzed situation concerns a real antenna, and its radiation into the reverberation chamber is modeled using Green's function of cavity. The numerical problem is solved by the method of moment. The model has been tested and is able to rigorously characterize the reverberating environment for the design and optimization of antenna configurations to be addressed in future studies.

Source Stirring Mode for Reverberation Chambers

The paper investigates the possibility of reverberating a shielded room by means of source mode stirring. The transmitting antenna position and orientation are randomly changed inside a sub-volume of the chamber. In general, antenna displacement can be achieved by a proper design of an array of antennas, where one or more antennas are activated at different time instants. This technique eliminates mechanical rotating paddles inside the chamber, and offers the advantage of a continuous wave (CW) operation with respect to the frequency stirring method. The preliminary experimental and simulated results encourage further investigation of the proposed technique.