使用一位元相位可切換之槽孔耦合貼片單元之波束掃描穿透陣列天線

Abstract

本論文提出一種使用一位元相位可切換之槽孔耦合貼片單元並且運用在波束掃描穿透陣列天線上，每一個單元由上下兩層矩形貼片天線及中間層的接地槽孔耦合所組成。每個貼片天線的中間切上一條橫向狹縫，以利於裝上負載變容二極體或電容器進而控制單元的穿透相位；為了進行初步驗證，採用裝有電容器以及無電容器的單元，作為提供兩種傳輸相位狀態，以至於實現一位元相位切換。未來，電容器可用變容二極體代替來實現即時的波束掃描穿透陣列天線。此外，我們也探討斜向入射波對單元效能影響，未裝上電容器的單元在大角度的斜向入射下會造成穿透相位的偏移，導致兩個狀態之間的相位差會窄於180°，此現象會在擺放單元於穿透陣列天線時納入考慮。 接下來，我們分析了設計使用一位元單元波束掃描穿透陣列天線時的重要條件。單元的穿透係數大小對於穿透陣列天線的增益極小地相關。然而，在單元中兩種狀態的較小相位差將會降低穿透天線增益並且增加旁辦電平。根據以上結論，我們提出了一套基於本文所提出的一位元相位可切換單元來設計波束掃描穿透陣列天線的系統化流程，結果表明出無裝上電容器的單元會受到斜向入射影響，應放置在穿透陣列天線的中央以增強性能。 在本論文的實驗驗證部分，我們提出了一個工作頻率為10GHz且由208個單元所組成簡化版的使用一位元相位可調單元的波束掃描陣列天線。模擬結果顯示，此穿透陣列天線可實現約80°的波束掃描範圍，並具有高於20 dBi的增益；製作且測試了基於本文所提出的一位元單元(裝有和不裝電容器)的兩種固定波束(波束方向為0°及20°)的陣列天線。在目標波束方向出測得的尖峰增益為分別為20 dBi和17.5 dBi。

A novel beam-steering transmitarray using 1-bit phase switchable aperture-coupled patch unit cell is presented. It consists of two identical, back-to-back rectangular patch antennas and coupled through the middle layer ground slot. To control the transmission phase of the transmitarray unit cell, each patch is cut into halves by a transverse slit, at the middle of which the varactor diodes or chip capacitors is loaded. For preliminary verification, the unit cell loaded with and without chip capacitors is adopted to provide two states of transmission phase to achieve 1-bit phase switching. In the future, the capacitors can be replaced by varactor diodes to accomplish real-time beam-steering transmitarray. In addition, the effect of the oblique incident wave on unit cell performance is also discussed. The unit cell without capacitors suffers from the transmission phase shift in large oblique incident angles, resulting in phase difference narrower than 180 between the two states. This will be accounted for when arranging the unit cell in transmitarray. Next, we analyze the important factors for designing a beam-steering transmitarray using 1-bit unit cell. The magnitude of the transmission coefficient of the unit cell is minimally relevant to the gain of the transmitarray. However, the smaller phase difference between the two states of the unit cells will lower the gain and increase the side lobe level of transmitarray. Above all, we propose a systematic process for designing a beam-steering transmitarray based on the proposed 1-bit phase switchable unit cell. It is shown that the unit cell without capacitors suffers from the effect of the oblique incidence and thus should be placed in the center part of a transmitarray to enhance the performance. A simplified beam-steering transmitarray composed of 208 1-bit phase switchable unit cells for operation at 10 GHz is designed. The simulations showed that it can achieve about 80° beam-steering angular range and higher than 20 dBi gain. Two test pieces of fixed-beam X-band transmitarray (0° and 20° from broadside, respectively) based on the proposed unit cell (loaded with and without capacitors) are fabricated and tested. The measured peak gains at the targeted beam directions, namely θ = 0°and θ = 20°, are 20 dBi and 17.5 dBi, respectively.