應用於無人機空間可重構相控陣列之融合超聲波及微波之相位同步系統

Ultrasound-and-Microwave-Fused Phase Synchronization System for Drone-Based Spatially Reconfigurable Phased Array

黃士銘(Shih-Ming Huang)

指導教授 ： 陳士元

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202202075

摘要

無人機載具有高機動性且外觀輕巧的優點，適合酬載第五代行動通訊(5G/B5G)的無線通訊設備，成為高機動性的空中基地台。然而，無人機的尺寸和載重能力，也限制了無人機可以承載天線的尺寸，進而降低了無線通訊的信噪比(SNR)和資料傳輸效率。做為解決方案，我們提出了基於無人機的空間可重構相控陣列（SRPArray）的概念，利用多台無人機各自攜帶多組天線並同步傳輸訊號，形成分佈式的相控陣列天線，使得SRPArray能夠在維持單個無人機小尺寸的前提下，形成等效更大的天線孔徑。此外，分散式的架構也提供了天線之間互相位移的可能性，為整個相控陣列的場型設計額外加入空間中的自由度。
在 SRPArray 中，無人機之間的相對定位技術是首要的挑戰，因為無人機之間的位置資訊是每台無人機調整訊號源相位的重要依據。在本論文中，我們提出了一種新穎的微波超聲波融合相位同步（UMPS）系統，用來提供精準且快速的定位並提供射頻訊號適當的相位補償。作為原型，用於一維定位的 UMPS的均方根定位誤差在 30 至 1330 mm的檢測範圍中，達到 14 mm，並成功同步了 433-MHz 連續正弦波信號，達成相位均方根誤差小於 7.5度，足以用來為SRPArray中的無人機群饋入正確相位的訊號，形成良好的場型。更進一步，我們基於一維 UMPS 原型開發了二維 UMPS 原型機。初步量測結果，在 100 至 550 mm區間內，二維 UMPS 模組的均方根測距誤差僅為 8.4 mm，均方根角度測量誤差為 0.044。在撰寫本文時，我們目前正在驗證二維 UMPS中射頻信號相位同步的性能。
基於二維 UMPS 原型模組的初步量測結果，我們可以用自主開發的軟體(SRPSim) 計算SRPArray的陣列因子的期望指向性。結果顯示，如果SRPArray配備2-D UMPS原型模組並且操作在射頻中心頻率低於2500 MHz的條件下，SRPArray陣列因子的指向性有90%的機率能保持在低於同尺寸理想相控陣列的指向性的1-dB 以內，幾乎相當於理想相控陣列的指向性。因此，我們認為二維UMPS的定位與相位同步功能，有很高的潛力能應用在於 SRPArray，用以穩定合成分散式相控陣列的等效孔徑。

關鍵字

天線 ； 分散式波束成形 ； 相位陣列 ； 相位同步 ； 無人飛行載具

並列摘要

Unmanned aerial vehicles (UAVs), with a low profile and high mobility, can serve as a platform for aerial base stations in 5G/B5G communications. Yet the size and payload constraints of UAVs limit the aperture size of on-board antennas and thus impede the signal-to-noise ratio (SNR) and efficiency of wireless transmission. To address this issue, we proposed the concept of a UAV-based spatially reconfigurable phased array (SRPArray), which synthesizes an aperture by distributed beamforming (DBF) of antenna elements separately carried by UAVs. The DBF enables the SRPArray to freely span a larger aperture without the need to increase the size of individual UAVs. Furthermore, by relaxing the limit on the spatial arrangement of antenna elements, each of which is carried by a UAV, the SRPArray can exploit the degree of freedom in the space domain to its maximum when reconfiguring its beam pattern.
In an SRPArray, the relative localization among distributed UAVs for proper phasing of the antenna elements is the top challenge for implementation. Therefore, in this thesis, we proposed a novel ultrasound-and-microwave-fused phase synchronization (UMPS) system as a solution. As a prototype, the UMPS for 1-D localization, or 1-D UMPS, exhibited a root-mean-square (RMS) positioning error of 14 mm with a detection range from 30 to 1330 mm and synchronized a 433-MHz continuous wave (CW) RF signal with an RMS phase error less than 7.5, which is sufficient for forming a satisfactory beam pattern with SRPArray. The 2-D UMPS prototype is also developed based on the 1-D UMPS design. The preliminary results show that the RMS ranging error of the 2-D UMPS module is only 8.4 mm with a detection range from 100 to 550 mm and the RMS angular error for direction-finding is 0.044. We are currently verifying the performance of RF signal phase synchronization in the 2-D UMPS.
Based on the preliminary results of the 2-D UMPS prototype module, the array factor of the SRPArray can be estimated using a self-developed program, called SRPSim. The results show that, if equipped with the 2-D UMPS prototype module and operating at a central frequency lower than 2500 MHz, the directivity of the array factor of the SRPArray has a 90% probability of being kept within 1 dB down compared to that when all the antenna elements are ideally positioned and fed with exactly the desired phases. Such a high probability indicates that the prototype UMPS system possesses satisfactory positioning and phasing performances for use in the SRPArray to stably synthesize the desired aperture, whose directivity remains comparable with the array formed by ideally positioned and phased elements.

並列關鍵字

antennas ； distributed beamforming ； phased arrays ； phase synchronization ； unmanned aerial vehicles

參考文獻

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