Advanced Beam Estimation for Antennas Via Patterned Coupling-Line Detection Board in Ka-Band
Article information
Abstract
In this research, we present an innovative method for estimating the beams of array antennas. Traditional beam analysis methods rely on placing receiving antennas in the far-field region, which requires moving or rotating the Tx or Rx, and using radiation pattern measurements. However, such methods often demand vast spatial requirements and the use of high-cost network analyzers. In contrast, the technique proposed in this study utilizes a board patterned with coupling lines strategically placed in the antenna’s near-field zone. Signals intercepted by these coupling lines undergo conversion into DC voltage via a power detector situated at the line terminus. Interestingly, this method enables beam estimation solely based on the DC voltage level output of the power detector, thus offering a cost-effective and space-efficient solution that represents a significant advancement from traditional beam estimation methods.
I. Introduction
The traditional method for measuring the radiation pattern of an antenna involves calibrating it using two standard antennas with known gains, followed by measuring the antenna under test (AUT), and then conducting a relative comparison considering the known gain values [1]. In addition, despite the recent development of relatively small chambers, such as the compact antenna test range (CATR), traditional methods dependent on farfield conditions require a large amount of space. For instance, precise measurements typically require an anechoic chamber consisting of an absorber to prevent radiowave reflections and a motor instrument to rotate the antenna. While this can result in accurate estimations of the beam of an antenna, this method has multiple drawbacks—extensive spatial requirements, high equipment costs, and long measurement durations. In addition, conventional near-field scanning methods require the use of high-end equipment, such as network analyzers or spectrum analyzers. Furthermore, it involves a time-consuming process since the measurement period is not short [2].
This paper proposes a novel approach for beam estimation. In contrast to conventional methods, the proposed technique adds a specialized board in the near-field region of the AUT. This board is patterned with metallic lines on both sides to facilitate coupling with the antenna. Using frequency selective surface (FSS) techniques, the width and spacing of the metallic lines, as well as the substrate thickness, are adjusted to ensure high transmission characteristics at the desired frequency bands [3]. High transmission is crucial in this regard because the energy radiated from the antenna might be reflected by the beam estimation board, which could affect the antenna and thereby lead to less accurate measurement results. Subsequently, the minimal energy radiated from the AUT is coupled via the metallic lines and transmitted to a power detector located at the line’s terminus. The RF signals conveyed to the power detector are then converted into DC voltage levels based on their amplitudes. By analyzing the DC voltage levels obtained from each coupling line, the tilting direction and gain magnitude of the array antenna’s beam can be estimated.
Similar to traditional methods, the proposed approach requires a calibration process. However, instead of a high-end network analyzer, it uses a power detector IC chip, whose advantages include easy measurement, minimal space occupancy, and cost efficiency. Therefore, while the precision of the proposed method might be relatively inferior to far-field measurements, it offers utility in mass production verification, such as for antenna-in-package (AiP). Furthermore, its embedded FSS structures make it suitable for conducting continuous operational checks of antenna performance, especially when applied to cases that house antennas, thereby aiding in malfunction detection.
II. Unit Cell and Detection Board Design
This study intended to design a beam estimation board for a 28 GHz AiP. Unit cell simulations were performed to confirm whether the metal coupling lines demonstrated FSS characteristics at 28 GHz [4, 5]. The substrate chosen was the TLY-5 (Taconic Inc., Petersburgh, NY, USA), which has a dielectric constant of 2.2 and a loss tangent of 0.0009. The substrate thickness was 1.52 mm. Identical metal coupling lines were centrally placed on the top and bottom surfaces of the substrate. Fig. 1 presents the reflection and transmission characteristics of the unit cell simulation, showing that it demonstrates high transmission properties at 28 GHz, where the polarization directions of the coupler line and the AUT are parallel. As a result, in Fig. 2, the coupler line of the detection board and the polarization of the AiP are arranged in such a way that they align with each other.
A detection board was designed to estimate the beam of a 1-by-4 antenna with dimensions of 24 mm by 6 mm operating at 28 GHz. The board was strategically positioned 8.7 mm above the array antenna in the near field. Notably, 8.7 mm was determined to be the position at which the maximum coupling coefficient reaches −30 dB when the antenna radiates toward boresight [6]. This configuration was established to minimize the influence of the detection board on the antenna’s radiation performance. Furthermore, the dimensions of the detection board were set to 50 mm by 50 mm to ensure sufficient coverage of the energy radiated by the AiP during beam steering. Drawing on the results of the unit cell simulation, the coupling lines patterned on the detection board were spaced at 5.2 mm intervals and oriented perpendicular to the plane on which the antenna executes its beam steering [7].
In addition, power detectors were mounted at four locations within the coupling lines on the detection board, as shown in Fig. 2. The power detector employed in this study was the ADL6010 (Analog Devices Inc., Wilmington, MA, USA) [8], which is capable of detecting signals ranging from 0.5 GHz to 43.5 GHz and measuring power levels from −30 dBm to +15 dBm. Fig. 3 shows that the coupler lines at the bottom of the board are connected to the RFIN pin of the power detector, while those on the board’s upper side are linked to the ground pin of the power detector. Overall, this configuration demonstrates the mechanism by which the RF signal received by the coupler line of the detection board can be converted into the DC voltage by employing a power detector.
III. Simulation and Measurement Results
The simulation and measurements conducted in this study were based on three different cases. Case 2 indicates a situation where the phase of the array antenna is consistent and radiates through boresight, while Cases 1 and 3 describe situations where the beam pattern tilts either left or right respectively. Fig. 4 shows the E-field distribution on the detection board. Although the beam synthesis is not complete due to the close range, a distinct E-field distribution is observed for each case. This highlights the differences in the energy radiated from the antenna, as well as the energy coupled to each coupling line, based on the beam state in the near-field region.
Fig. 5 compares the simulation and measurement results. The simulation results show the coupling coefficient of the four patch antennas at the location of the power detector, calculated as the sum of their S-parameters. The power levels detected by the power detector were determined by adding the coupling coefficient to the antenna’s input power level. This power level was then transformed into DC voltage [9], indicating that the DC voltage level could be used to estimate the power received by each coupling line. In Fig. 5 and Tables 1 and 2, variations in the coupling coefficient and detected power levels are observed at different positions based on the direction of beam formation. Fig. 5 exhibits a notable drop in value at position (c) for Case 1, which can be attributed to the power detector exceeding the detection range. This can be addressed by elevating the input power level to ensure that it falls within the detection range of the power detector.
Fig. 6 and Table 3 show that the detected power levels vary with changes in the input power when the array antenna is set to a consistent phase, such as in boresight conditions. These results highlight the capability of the proposed method to detect a 1-dBm change in input power. Furthermore, combining the results from Figs. 5 and 6, it was observed that the beam pattern and gain of the array antenna could be roughly determined, even in near-field regions. Fig. 7 displays the fabricated model of the detection board and the experimental setup for measuring AUT performance, with the detection board mounted on it. Fig. 8 shows the radiation pattern measurement results of the AUT, both with and without the detection board attached. Whether in boresight or when the beam tilts left or right, the presence of the detection board does not impact AUT performance significantly [10]. These findings suggest that adding the detection board to an antenna case or a radome only minimally affects radiation performance [11].
Table 4 presents a comparative analysis of various antenna radiation performance measurement techniques [12, 13], including anechoic chamber [14], CATR anechoic chamber [15], near-field measurement system [16], and the coupling line detection board proposed in this paper. This comparison was conducted based on factors such as size, required equipment, cost, and measurement bandwidth. Among these, the coupling line detection board is especially notable for its small size and simplicity, which offer significant advantages in practical applications. Unlike the other methods, which require complex and expensive equipment, such as network analyzers and positioners, the proposed method only requires a signal generator and a power detector, resulting in considerably lower costs. Furthermore, its ease of use makes beam pattern estimation both efficient and accessible. However, it is important to note that the coupling line detection board operates within a narrower bandwidth than the other methods. This limitation indicates its suitability for specific applications that require only basic functionality and fault detection rather than a broad-spectrum analysis. Despite its limitations with regard to bandwidth and application scope, the cost-effectiveness and simplicity of the proposed method make it an attractive option for use in situations in which budget and space constraints are key considerations.
In summary, while the proposed method cannot replace traditional methods that provide accurate measurements of AUT performance, it offers a practical solution for verifying AUT functionality in limited spaces at a reduced cost.
IV. Conclusion
In this study, we verified the feasibility of estimating the beam pattern of an AUT without using expensive RF equipment by employing a detection board. Compared to traditional measurement techniques, the proposed approach offers the advantages of miniaturization and reduced system establishment costs. As a result, it is anticipated to have a wide range of applications. For instance, it can be utilized as a large-scale validation system in the mass production process of AiP. Moreover, when integrated with an antenna’s casing or radome, it enables real-time tracking of antenna performance, thus allowing the immediate detection of malfunctions or failures [17].
Acknowledgments
This work was supported by a grant-in-aid from LIG Nex1.
References
Biography
Seokyeon Hong, https://orcid.org/0009-0000-2756-5798 received his B.S. degree in electrical and electronic engineering from Yonsei University, Seoul, Republic of Korea, in 2018, and his M.S. degree in electrical and computer engineering from Seoul National University, Seoul, in 2020. In 2020, he joined Samsung Electronics in Suwon, Republic of Korea, where he was involved in the design of a 5G flagship smartphone, specifically dealing with its RF radiation aspects. In 2023, he joined the Korea Electronics Technology Institute, Seongnam, Republic of Korea, where he was involved in research on antennas, metasurfaces, and reconfigurable intelligent surfaces. He is currently working as a senior researcher at the ICT Device and Packaging Research Center. His current research interests include liquid crystal phase shifters, 5G mmWave beamforming antennas, and reconfigurable intelligent surfaces.
Seunggoo Nam, https://orcid.org/0000-0003-2233-6392 received his B.E. degree in computer and communication engineering from Korea University, Seoul, Republic of Korea, in 2015. He received his Ph.D. in radio communications engineering from Korea University, Seoul, Republic of Korea, in 2020. In 2020, he joined Samsung Electronics, Suwon, Republic of Korea, where he was involved in the design of a 5G mmWave front-end module. In 2021, he joined the Korea Electronics Technology Institute, Seongnam, Republic of Korea, where he was involved in research activities focused on antennas, frequency tunable filters, and convolutional neural networks for deep learning. He is currently a senior researcher at the ICT Device and Packaging Research Center. His current research interests include K-band frequency tunable filters, array antennas, and the 5G mmWave module.
Sehwan Choi, received his M.S. degree in mmWave engineering from the Gwangju Institute of Science and Technology (GIST), Republic of Korea, in 2003. He received his Ph.D. in radio communications engineering from Hanyang University, Seoul, Republic of Korea, in 2017. In 2004, he joined the Korea Electronics Technology Institute, Seongnam, Republic of Korea, where he was involved in research on antennas, front-end modules, and beamformers. He is currently the team leader of the ICT Device and Packaging Research Center. His current research interests include 5G passive beamformers, liquid crystal phase shifters, and reconfigurable intelligent surfaces.
Jihan Joo, received his B.S. degree in electrical engineering from Chungbuk National University, Cheongju, Republic of Korea, in 2002, and his M.S. and Ph.D. degrees from the Department of Radio Science and Engineering, Kwangwoon University, Seoul, Republic of Korea, in 2008. He is currently a chief research engineer at LIG Nex1. His research interests focus on RF seeker design, including microwave active module design and highly efficient solid-state power amplifier (SSPA) design for application in radar and M/W seeker systems.
Jaesub Han, received his B.S. degree in information and communication engineering from Soongsil University, Seoul, Republic of Korea, in 2005, and his M.S. degree in telecommunication engineering from Yonsei University, Seoul, Republic of Korea, in 2020. In 2007, he joined LIG Nex1, Yongin, Republic of Korea, where he has been involved in research activities focused on active phased-array antenna systems, RF modules, SSPA, and MMIC. He is currently the team leader of the Microwave R&D center in LIG Nex1. His current research interests include antenna-in-package and Ka-band AESA systems