使用空氣填充式基板集成波導結構之毫米波波束成形天線陣列

Abstract

隨著時代的進步及行動通訊需求大量增加，第五代行動通訊技術利用毫米波段中的部分頻譜來增加通信容量、降低功耗、提高資料傳輸速率和減少延遲。其中透過波束成形技術可以鎖定特定區域，來改善基地站無法涵蓋之區域的傳輸速率，而波束成形是藉由調整多個天線的輸入訊號大小與相位權重，以控制主波束的方向。巴特勒矩陣是其中一種可以達到此種目的的電路，且巴特勒矩陣使用元件數較少、損耗較小、以及較便宜。另外，為了降低功耗，需減少傳輸路徑上的損耗，因此本文採用空氣填充式基板集成波導結構來設計巴特勒矩陣饋入陣列天線，以達到波束成形功能，以及降低損耗之特性。 傳統波導管之體積較笨重、耗費較高又無法與平面集成。為了有利於封裝整合，因此衍生出基板集成波導結構的設計。該結構利用基板上下兩層的全金屬，配合兩側穿層的金屬柱作為金屬牆，形成一個可以與平面集成體積較小又低成本的平面波導結構。由於基板集成波導在傳輸過程中會接觸到有損介質，且在高頻時，有損介質材料的損耗大，因此造成能量在傳輸過程大量損耗。為了降低損耗，因而衍生出本文採用之空氣填充式基板集成波導結構。該結構將傳統基板集成波導之有損介質基板改為空氣基板，由於有損介質材料的損耗大於空氣，因此空氣填充式基板集成波導結構可以降低傳輸過程產生的損耗。 巴特勒矩陣是由耦合器、交叉耦合器以及相移器所組成的，其中本論文所使用的相移器為短截線相移器。本論文針對此相移器進行分析，並建立其等效電路模組，以此模組設計出可應用於空氣填充式基板集成波導結構的巴特勒矩陣之相移器。 為了驗證空氣填充式基板集成波導結構損耗較低，因此利用空氣填充式基板集成波導結構設計四乘四巴特勒矩陣饋入陣列天線，經模擬得知，在60 GHz時，此設計電路之損耗低於1 dB，與參考文獻中，使用傳統基板集成波導設計之巴特勒矩陣相比明顯小1 dB，因此證實使用空氣填充式基板集成波導結構設計出來之四乘四巴特勒矩陣之損耗較低，而將此電路饋入陣列天線，不但具有波束成形功能，又低損耗，且應用於毫米波頻段。

With the advancement of the times and the increasing demand for mobile communications, the fifth-generation mobile networks will utilize part of the spectrum in the millimeter-wave (mm-Wave) band to increase communication capacity, reduce power consumption, increase data transmission rate, and reduce delay. The beamforming technology can specify a specific area to improve the transmission rate of an area that cannot be covered by the base station. And beamforming controls the direction of the main beam by adjusting the input signal magnitude and phase weight of multiple antennas. The Butler Matrix is one of the circuits that can achieve beamforming. The Butler Matrix uses fewer components, less loss, and is less expensive. In addition, in order to reduce power consumption, it is necessary to reduce the loss on the transmission path. Therefore, this thesis uses an air-filled substrate integrated waveguide (AFSIW) structure to design an extremely low loss Butler matrix feeding beamforming antenna array. Traditional waveguides are bulky, expensive, and can’t be integrated with the plane. In order to make package integration easy, the design of the substrate integrated waveguide (SIW) structure is evolved. The structure utilizes the full metal of the upper and lower layers of the substrate, and the through-hole via on the two sides is used as the metal wall to form a planar waveguide structure which can be integrated with the plane and has a small size and low cost. However, due to the contact with the lossy substrate or air during the transmission, there is still a non-negligible power loss when applied in high frequencies. In order to further reduce losses, the AFSIW structure is evolved on this thesis. The AFSIW structure changes the lossy dielectric substrate of the conventional SIW into the air. Therefore, the AFSIW structure can avoid the loss from substrate and achieve better performance than traditional SIW. Butler matrix is composed of the coupler, the crossover and the phase shifter. The stub phase shifter is used in this thesis. In this thesis, the stub phase shifter is analyzed and the equivalent circuit module of the stub phase shifter is established. The module is designed to apply in the phase shifter of the Butler matrix on AFSIW structure. In order to verify that the structure of the AFSIW has low loss, a 4×4 Butler matrix feeding array antenna is designed by using an AFSIW structure. The simulation shows that the loss of this design circuit is less than 1 dB at 60 GHz, which is significantly smaller than the traditional SIW Butler matrix 1 dB. Therefore, it is confirmed that the loss of the 4×4 Butler matrix designed using the AFSIW is low. And the extremely low loss Butler matrix feeding beamforming antenna array is applied in the millimeter-wave band.