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This paper proposes a reverberation chamber structure consisting of new reflectors and mode stirrers for electromagnetic compatibility and wireless terminal measurements. The key design considerations for them are determined through a reasonable approach to analyze the eigenmode for a reverberation chamber and the standard deviation of its working volume based on 3D simulation. The final designs are expected to improve the standard deviation performance of the initial structure of the reverberation chamber and provide a better mode stirring environment. The results measured in the fabricated chamber demonstrate that these predictions are clearly realized. The results satisfy the main requirements of this paper, which are defined in consideration of the specifications of commercial reverberation chamber products. Therefore, the reverberation chamber of this paper is expected to be useful for performance measurement and evaluation of commercial wireless terminals. To verify this logical approach to obtain a good design and its results, the results measured in the actual fabricated reverberation chamber are described along with analytical and computational results.

Unlike previous generations, 5G network is characterized by the provision of innovative services rather than technological advances [

The AC has been considered the only way to measure the 5G devices. However, to overcome drawbacks of AC as well as considering the real communication environment, recently the RC attracts a huge attention. The RC is an important alternative measurement instrument for the measurement and application of small antennas for wireless and mobile terminals and for realistic evaluation of SISO to MIMO devices below the current 4G standard, as is well known through the IEC 61000-4-21 standard [

The most important consideration for the intended measurement tasks and applications in these fields is to design an RC appropriately so that it satisfies the user's requirements. The standard provides requirements of acceptable RC performance and basic guidelines for RC design to meet these requirements. Indeed, there are no indicators to objectively evaluate RC performance beyond the requirements of the standard in modeling for RC construction. Also, even if an RC is designed much more stringently than the requirements proposed in the standard, this does not prove that it can achieve superior performance in comparison to other RCs. In other words, comparing the performance of different RCs, including their physical parameters, can be quite difficult, and there are no theoretically standardized formats or guidelines on how to carry out RC modeling to achieve better performance.

In this respect, it can be said that the design of an RC with excellent performance is virtually impossible without an initial reference structure. Based on an initial structure that satisfies the basic standard guidelines, the specific design of an RC should follow a reasonable structure design process to modify it until the user’s own requirements are satisfied. The derivation of this initial structure and the logical process for its improvement are dependent on known rules of thumb or unknown rules of thumb [

This paper proposes a new RC structure for EMC and wireless device measurements. As mentioned above, the requirements for an RC have been established and its initial structure has been determined through the references and the rules of thumb. Based on the initial structure, a reasonable approach using field uniformity and eigenmode analysis in the RC has resulted in the final structure that satisfies the requirements and shows improved performance compared to the initial one. Another objective of this paper is to show that this approach for superior design will improve the previous results in a way that compares relatively well with the current theoretical results. To verify the performance of the final structure, experimental results of the constructed prototype are presented along with simulation results.

Considering the requirements of the IEC 61000-4-21 standard, the requirements of RC to be developed in this work are shown in Table

Requirements of reverberation chamber to develop.

Items | Requirements |
---|---|

Start operating frequency | 650 MHz |

| |

Overall volume | 5.05 m^{3} |

(Internal dimensions) | (1.4 m × 1.95 m × 1.85 m) |

| |

Working volume | 0.76 m^{3} |

(Rectangular dimensions) | (0.835 m × 0.951 m ×0.954 m) |

| |

Standard deviation | Less than 2.5 dB |

The working volume of the RC can be located at a distance greater than

To do this, commercial RCs (whose overall size and the working volume dimensions are published) were investigated, and the ratio between them was analyzed. This is not based on theoretical grounds, but only to figure out the average level of the ratio from those designed cases. In the case of Siepel models, EOLE80, EOLE200, EOLE400, and EOLE1000 models, the ratios were approximately 10%, 17%, 19%, and 16%, respectively [

The number of modes

Theoretical number of modes for a reverberation chamber of the size considered in this paper.

The basic prototype of the RC that reflects the dimension requirements in Table

Basic prototype of a reverberation chamber proposed in this paper.

Stirrer 2 is horizontal to the bottom of the chamber and consists of four rectangular planes. Taking into account operation at the higher frequency and the asymmetry of stirrer 1, each plane has a width (

Design parameters for the basic prototype of the reverberation chamber.

Parameter | Length, m | Parameter | Length, m |
---|---|---|---|

| 1.85 | | 0.34 |

| 1.4 | | 0.16 |

| 1.95 | | 0.31 |

| 0.954 | | 0.3 |

| 0.835 | | 0.3 |

| 0.951 | | 0.36 |

| 0.46 | | 0.2 |

| 0.46 | | 0.2 |

| 0.4 | | 0.7 |

| 0.4 | | 0.2 |

| 0.35 | | 0.364 |

| 0.36 | | 0.8 |

To investigate the level of field uniformity of the basic prototype as described in Introduction, a commercial software package FEKO as the simulation kernel, which is based on a frequency domain method of moment (MOM), is used [

For the simulation of the materials in the closed structure, a free space condition with a relative permittivity of

The simulations were performed at a total of nine frequencies at 25 MHz intervals from 650 MHz to 850 MHz. The reason is that for 850 MHz and above, the mesh size generated in the RC requires much more resources to compute. A log-periodic dipole array (LPDA) antenna was used as a transmitting antenna for the simulations. It consisted of 18 dipole elements, and it was realized by impedance matching through the transmission line network. At each calculation frequency, a total of twenty simulations were performed as the stirrers rotated at 18° intervals. Then, the standard deviation representing the field uniformity of the RC was computed according to the IEC 61000-4-21 standard after postprocessing collecting the electric field data from twenty simulations.

The results are shown in Figure

The simulated E-field standard deviation for working volume of the basic RC structure.

The approach to improve the field uniformity of an RC can be roughly divided into two main aspects. One of them is to implement the appropriate reflectors by effectively utilizing the empty spaces on the RC walls. The other is to design efficient mode stirrers. This part describes the results for the former. As shown in Figure

The reflector structures and their positions applied to these spaces are shown in Figure

RC structure with reflector 1 and 2.

Figure

Standard deviation calculated according to the number of reflector 1 when there is no reflector 2. (a) 2. (b) 4. (c) 6. (d) 8. (e) 10. (f) 11. (g) 13. and(h) 16.

The results indicates that when six type 1 reflectors are located on the left wall as shown in Figure

Design parameters related to the reflectors within the reverberation chamber.

Parameter | Length, m | Parameter | Length, m |
---|---|---|---|

| 0.324 | | 1.75 |

| 0.324 | | 0.03 |

| 0.36 | | 0.461 |

| 0.71 | | 0.05 |

| 0.34 | | 0.05 |

| 0.538 | | 0.05 |

| 0.042 | | 0.22 |

Placing reflector 2 shown in Figure

As described above, the standard deviation analysis method of the working volume for evaluating field uniformity is very intuitive, but it does not provide a valuable insight into the physical principles caused by changes in structures, including mode stirrers inside an RC. In addition, the method requires extensive computation time, computational resources, and complex postprocessing. From this point of view, eigenmode analysis is very effective for the design of mode stirrers or reflectors in an RC. According to this technique, the design with the maximum amount of eigenfrequency shifts is the optimal choice, which allows designers to quickly and easily evaluate designs. This was confirmed in [

It should be noted that it is very difficult to quantitatively define the correlation between the eigenfrequency shift and the standard deviation of the field uniformity. Therefore, the eigenfrequency and standard deviation should be analyzed together based on the reference structure, for example, as shown in Figure

For the calculation of eigenfrequencies according to the number of type 2 reflectors, their width (

Dimensions for width and gap of type 2 reflectors for the eigenfrequency shifts analysis according to their number.

Number of Reflector 2 | | | Other Parameters |
---|---|---|---|

4 | 0.24 | 0.24 | Same as Table |

5 | 0.24 | 0.12 | |

8 | 0.12 | 0.12 | |

9 | 0.12 | 0.06 | |

11 | 0.06 | 0.12 | |

12 | 0.12 | 0.03 | |

21 | 0.06 | 0.03 |

Dimensions for width and gap of type 2 reflectors for the eigenfrequency shifts calculations.

Number of Reflector 2 | | | Other Parameters |
---|---|---|---|

2 | 0.7 | 0.36 | Same as Table |

0.76 | 0.24 | ||

0.86 | 0.12 | ||

| |||

3 | 0.27 | 0.5 | Same as Table |

0.34 | 0.4 | ||

0.41 | 0.3 | ||

0.461 | 0.12 | ||

0.461 | 0.22 |

Eigenfrequency shifts calculated to determine the dimensions of reflector 2. (a) Results for the conditions in Table

The numerical results shown in Figures

In the RC shown in Figures

Figure

Final reverberation chamber structure with dual-plate type mode stirrers for fabrication.

Calculated eigenfrequency shifts for RC with stirrers 1 and 2 in dual-plate form (a) when

The eigenfrequency shifts for the final design shown in Figure

Eigenfrequency shifts for the final design compared to those of two other conditions shown in Figure

The standard deviations calculated through 3D simulations and postprocessing to confirm the field uniformity performance of the final design are shown in Figure

Calculated standard deviations for the RC (a) with reflector 1, (b) with reflectors 1 and 2, and (c) with the new stirrers and the reflectors, the final design.

The final design shown in Figure

Photographs of the fabricated reverberation chamber.

Photograph of the LPDA antenna developed to evaluate the performance of the proposed RC.

To evaluate the field uniformity performance of the proposed RC, the maximum electric field values were measured at eight corners of the working volume shown in Figure

Figure

Measured standard deviations for the RC (a) with the reflectors and the original stirrers and (b) with the reflectors and the new stirrers, the final design. (c) Comparison between

An RC consisting of new reflectors and mode stirrers has been proposed. It has an inner size that is approximately the same as or smaller than that of a commercial product. The main parameters for the reflectors and mode stirrers were determined through a logical approach based on standard deviation and eigenfrequency shift analysis by 3D simulations. The calculated and measured standard deviations for field uniformity evaluation of the proposed RC have demonstrated that they clearly improve the standard deviation performance of its initial structure. In addition, the reasonable approach proposed in this paper for the RC design is very effective, and it has been verified that the design results accurately predict the main results obtained from the actual measurements. The measured results for the standard deviation of the proposed RC were found to satisfy all of the requirements defined in this paper. Therefore, it is expected that the performance of the proposed RC could be a very attractive facility for users who want to measure and evaluate the performance of commercial wireless terminals.

The data used to support the findings of this study are available from the corresponding author upon request.

The authors declare that they have no conflicts of interest.

This work was supported by Institute for Information & Communications Technology Promotion grant funded by the Korea government (no. 2015-0-00855, Study on Measurement and Evaluation Technology based on Reverberation Chamber, and no. 2017-0-00982, Development of System-Level Technology for Protection Design and Performance Evaluation against EMP). The authors are grateful to the staff of Korea Shield System Co., Ltd., the homepage of which is www.kshieldsysltd.com, for their help concerning the measurements in the reverberation chamber in this study.

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