薄型寬頻微小化貼片式天線於第五代行動通訊手機應用

Thin, Wideband and Miniaturized Patch Antenna for 5G Mobile Application

劉鴻軒(Hung-Hsuan Liu)

指導教授 ： 唐震寰

國立交通大學/電機學院/電信工程系所/碩士(2020年)

摘要

在毫米波頻段下的手機天線，使用相位式天線陣列，一方面可提升增益彌補毫米波頻段的傳播損耗，二方面可提供切換波束的功能。近年智慧型手機朝薄型化發展，而加入了許多功能模組，如多攝像頭、Face ID和第五代行動通訊系統等，導致手機的可運用空間被壓縮，因此如何微型化及薄型化天線陣列成為的關鍵議題，所幸有軟板的問世，由於該板材特性較硬板輕薄且可彎曲，並能與周邊物體契合，因此有較高的空間利用度，目前各大手機業者已使用軟板做為天線載板，並整合於零件滿佈的手機之中。然而，軟板為了維持彎曲的特性，通常設計得較薄且有金屬層數的限制，此限制使得貼片式天線難以寬頻，再者若考量毫米波天線陣列的需求，天線尺寸需要微小化，因此如何在有限的板厚及金屬層數下，設計寬頻、薄型及微小化的貼片式天線便是設計的重點。
貼片式天線具有薄型的優點，且易整合於平板結構，但貼片式天線薄型的特色使天線的品質因子(Q Factor)較大，導致貼片式天線的頻寬較窄，因此有許多文獻針對薄型貼片式天線的寬頻方法做研究與探討，常使用的方法有：1.多模態貼片式天線 2.寄生式貼片天線 3.週期性結構天線。多模態貼片式天線為了激發出高階模態，天線尺寸必須大於一個空氣波長，導致天線有旁波瓣的產生，且由於尺寸過大，不利於形成天線陣列，不適合做為毫米波頻段的應用。寄生式貼片天線利用電容性耦合激發寄生貼片，產生新的共振頻率點，但需要在頻寬與天線尺寸之間做取捨，若希望獲得足夠的頻寬會使天線尺寸過大，不利於形成天線陣列。週期性結構天線透過其週期性結構產生色散效應，使傳播常數隨頻率改變而改變，藉此拉近各個模態的頻率點，以提升頻寬，然而此方法所形成的天線尺寸依然超過天線陣列的要求。
本論文參考寄生式貼片天線做為做為初步構想，由於需要在天線尺寸與頻寬之間做取捨，本論文將寄生貼片式天線調整至較小尺寸時，再加入蜿蜒式隙縫至寄生貼片中，透過增加電容性的耦合量，以產生新的共振頻率點，藉此增加天線的頻寬，並縮減整體天線面積，使天線能符合毫米波天線陣列的尺寸規格。
本天線希望能用軟板實現，但受限於國內軟板廠商製作時程的配合，本研究仍採用具軟板規格之硬板實現本論文之創新天線。本天線使用硬板EM-890K做為天線基板，其介電係數、板材厚度和金屬層數皆與液晶聚合物(Liquid Crystal Polymer, LCP)軟板之特性參數與結構相同：介電係數3 vs. 3、板材厚度0.4 mm vs. 0.4 mm及金屬層數3 vs. 3。製
作出天線大小僅6×5.76×0.40 mm3(0.56×0.54×0.04λ3)，為單層介質板結構，量測的頻率範圍為26.2-29.3 GHz，由於製程的變異，導致頻率的偏移，所以將變異部分代回模擬，再與量測結果比對，其符合量測結果，因此原設計滿足5G NR的n257之頻帶。輻射場形為broadside方向，頻帶內的增益界在3.7-6.5 dBi之間，具有良好的輻射特性。本天線特色
在於具有更小的尺寸使其容易製作成天線陣列，並能於軟板上實現，適合做為毫米波手機天線應用。本天線的設計細節和實驗結果在論文中皆有詳細討論。

關鍵字

薄型 ； 寬頻 ； 微小化 ； 貼片式天線 ； 第五代行動通訊 ； 軟板

並列摘要

Mobile phone antennas in the millimeter wave band use phased antenna arrays, which can increase the gain on the one hand to compensate for the propagation loss in the millimeter wave band, and on the other hand, it can provide the function of switching beams. In recent years,
smart phones have become thinner, and many functional modules have been added, such as multi-cameras, Face ID, and fifth-generation mobile communication systems. As a result, the usable space of mobile phones has been compressed, so how to miniaturize and thin the antenna
array has become a key issue. Fortunately, the advent of the flexible board, because the board is thinner and more flexible than the rigid board, and can fit with surrounding objects, so it has a high degree of space utilization. At present, major mobile phone manufacturers have used flexible boards to make an antenna carrier board and integrated into a mobile phone with a lot
of parts. However, in order to maintain the bending characteristics, flexible boards are usually designed to be thin and have a limit on the number of metal layers. This limitation makes it difficult for patch antennas to have a wide bandwidth. Furthermore, considering the
requirements of millimeter wave antenna arrays, the antenna size needs to be miniaturized.
Therefore, how to design a wideband, thin and miniaturized patch antenna with limited board
thickness and metal layers is the focus of design.
The patch antenna has the advantages of being thin and easy to integrate in a flat structure. However, the thin characteristics of the patch antenna make the antenna's Q Factor larger, which results in a narrower patch antenna bandwidth, so there are many literature studies and discusses the broadband method of thin patch antennas. The commonly used methods are: 1. multi-mode patch antenna 2. parasitic patch antenna 3. periodic structure antenna. In order to excite high order modes of a multi-mode patch antenna, the antenna size must be larger than an air wavelength, which causes the side lobe of the antenna. Because the size is too large, it is not
conducive to the formation of an antenna array, and is not suitable for applications in the millimeter wave band. . Parasitic patch antennas use capacitive coupling to excite parasitic patches and generate new resonant frequency points, but a trade-off needs to be made between the bandwidth and the size of the antenna. If you want to obtain sufficient bandwidth, the antenna size will be too large, which is not conducive to the formation Antenna array. The periodic structure antenna produces dispersion effects through its periodic structure, so that the propagation constant changes with frequency, thereby approaching the frequency points of each mode to increase the bandwidth. However, the size of the antenna formed by this method still exceeds the antenna array. Requirements.
In this paper, a parasitic patch antenna is used as a preliminary idea. As a trade-off between antenna size and bandwidth is required, this paper adjusts the parasitic patch antenna to a smaller size, and then adds a serpentine slot to In the parasitic patch, the capacitive coupling is increased to generate a new resonance frequency point, thereby increasing the bandwidth of the
antenna and reducing the overall antenna area, so that the antenna can meet the size specifications of the millimeter wave antenna array.
This antenna is expected to be implemented with a flexible board, but is limited by the production schedule of domestic flexible board manufacturers. This study still uses a rigid board with a flexible board specification to implement the innovative antenna of this paper. This antenna uses a hard board EM-890K as the antenna substrate. Its dielectric coefficient, sheet
thickness and number of metal layers are the same as those of the Liquid Crystal Polymer (LCP) flexible board. 3. Sheet thickness 0.4 mm vs. 0.4 mm and metal layer number 3 vs. 3. The antenna size is only 6 × 5.76 × 0.40 mm3 (0.56 × 0.54 × 0.04λ3), which is a single-layer
dielectric plate structure. The measured frequency range is 26.2-29.3 GHz. Due to the process variation, the frequency is offset, so Substitute the mutated part back to the simulation, and then compare it with the measurement result, which is consistent with the measurement result, so the original design meets the n257 frequency band of 5G NR. The radiation field is in the
broadside direction, and the gain boundary in the frequency band is between 3.7-6.5 dBi, which has good radiation characteristics. The antenna is characterized by its smaller size, which makes it easier to make an antenna array, and can be implemented on a flexible board, which is suitable for use as a millimeter wave mobile phone antenna. The design details and experimental results of this antenna are discussed in detail in the paper.

並列關鍵字

Thin ； Wideband ； Miniaturized ； Patch antenna ； 5G ； Flexible substrate

參考文獻

[1] Ojaroudiparchin, N., Shen, M., Zhang, S., et al.: ‘A switchable 3-D-coveragephased array antenna package for 5G mobile terminals’, IEEE Antennas Wirel. Propag. Lett., 2016, 15, pp. 1747–1750

[2] W. Hong, K.-H. Baek, and S. Ko, ‘‘Millimeter-wave 5G antennas for smartphones: Overview and experimental demonstration,’’ IEEE Trans. Antennas Propag., vol. 65, no. 12, pp. 6250–6261, Dec. 2017.

[3]http://pg.jrj.com.cn/acc/Res/CN_RES/INDUS/2018/3/6/cf603774-4cd7-4dbc-86e1f2547eefcef7.pdf

[4] Matthew A. Mow, Basim H. Noori, Ming-Ju Tsai, Han, Lee, &Pascolini (2018). United States Patent No.0026341 [5] R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna Design Handbook. Boston, MA, USA Artech House, 2001.

[6] L. Minz, R. S. Aziz, M. T. Azim, and S. O. Park, ‘‘Wideband aperturecoupled stackpatch antenna design with characteristic mode analysis,’’ in Proc. IEEE Int. Conf. Consum. Electron.-Asia (ICCE-Asia), Jeju, South Korea, Jun. 2018, pp. 206–212.