以低成本多層印刷電路基板中之新型無通孔空氣波導於毫米波和次太赫茲頻率下實現低電磁傳播損耗

Abstract

隨著第六代（6G）通訊系統、物聯網(IoT)、智慧家居/城市等的到來，對具有更寬頻寬和更快數據速率的短距離無線系統的需求比以往任何時候都更高。與傳統微波系統相比，毫米波（mmW）和次太赫茲（sub-THz）通訊系統因為頻率增加而具有提供更高頻寬的潛力，能夠滿足用戶的需求。在這些頻率上，需要使用封裝天線技術（AiP）來縮裝射頻系統並減少不必要的功率損耗。AiP允許在多層PCB結構中整合波束成形網絡、高增益相控陣列天線和射頻單元。在AiP封裝中，決定整體系統性能的一個關鍵組件是傳輸線。基於介電質的傳輸線在高頻時具有較大的損耗。將空氣波導引入多層PCB結構並將其用作傳輸線是一個機會，因為空氣填充波導(AFW)的尺寸可以減小到幾個毫米。在這樣的結構中，其中一個重要挑戰是無縫隙連接頂部和底部金屬層以形成波導的側壁。作為側壁的通孔是一個常見的做法，但高頻時所需的通孔尺寸和間距可能會超出製造能力。此外，所需的通孔數量將非常龐大，增加了設備的整體成本。基於電磁能隙(EBG)結構的解決方案使用通孔作為側壁，並利用電磁能隙的特性減少通孔與基板之間的泄漏。這些電磁能隙元件在其單元中包含通孔，其尺寸相當於半個波長。因此，在本論文中提出了一種基於縮小尺寸且無通孔的平面人造磁導體（AMC）的解決方案，用於在多層基板中創建空氣波導(AFW)。模擬和實驗結果顯示了所提出結構在低成本FR4基板上的優越性能。基於所提出的技術，探討了毫米波和次太赫茲頻率下多層AFW結構的各種拓撲。另外，研究與3D列印的整合可能性，比較所提出基於AFW的平面縫隙(slot)陣列天線有無3D列印製成的號角天線兩種情況。

With the arrival of the sixth-generation (6G) communications system, Internet of Things (IoT), smart home/city, etc., the demand for short-range wireless systems with higher bandwidth and faster data rates is higher than ever. Compared to traditional microwave systems, millimeter wave (mmW) and sub-THz communications systems have the potential to meet user demands as they inherently provide higher bandwidths due to increased frequency. Antenna-in-package (AiP) solutions are necessary at these frequencies to compact the RF systems and reduce unwanted power loss. AiP allows seamless integration of a beamforming network and a high-gain phased array of antennas with RF units in a multilayer PCB structure. One of the critical components determining the overall system’s performance in an AiP package is the transmission line. The dielectric-based transmission lines are lossy at high frequencies. Hence, it presents an opportunity to incorporate air waveguides into multilayer PCB structures and use them as transmission lines as the dimensions of air-filled waveguides (AFW) reduce to a few millimeters. One of the significant challenges in such structures is to seamlessly connect the top and bottom metal layers to form the sidewalls of the waveguide. Vias as sidewalls are an obvious choice. However, the required dimensions and spacings between vias at higher frequencies may reduce beyond the manufacturing capability. Also, the number of vias required will be huge and increase the overall cost of the device. The EBG-based solutions use vias as sidewalls and reduce leakage through the junction of the substrates using the EBG properties. These EBG elements contain vias in their unit cell, and their dimensions are comparable to half of the wavelength. Hence, a miniaturized vial-less planar artificial magnetic conductor (AMC) based solution to create AFW in a multi-layer substrate is presented in this thesis. Simulations and experimental results show the proposed structure's superior performance with low-cost FR4 substrates. Various topologies of multilayer AFW structures at mmW and sub-THz frequency are discussed based on the proposed technology. The possibility of integration with 3D printing is investigated. Planar slot array antenna using the proposed AFW with and without a 3D-printed horn cap is also studied.