毫米波頻段透鏡式天線陣列與波束成型演算法

Abstract

近年來，隨著通訊技術邁入5G時代，更高頻的頻段被運用在通訊系統中，帶來了更高衰減損耗的同時，也擁有著通道容量增加與天線尺寸縮小化的好處；因此，透過多個天線單元彌補增益的主動式陣列天線得以在商用領域實現應用。本論文發展了一項毫米波頻段的透鏡式雙極化8x8收發陣列天線結構，搭配基於差分進化演算法之波束成型優化技術，其操作頻段為26.5GHz-29.5GHz。關於陣列天線，本論文以瑞薩電子公司的波束成型晶片為主體完成了8x8毫米波陣列天線的設計，擁有良好的阻抗匹配，在一塊單獨的十層電路版上整合了主動式陣列天線、升降頻模組、電源和控制晶片，這有助於提升產品穩定性，並為之後與透鏡整合降低難度。唯因產品生產時程問題，本論文尚不能呈現該陣列天線之量測結果。在透鏡方面，配合8x8陣列天線的兩種近似球體與圓柱型的鐵氟龍透鏡結構被提出，其結構簡單卻能有效提升主動式陣列在部分掃描角度的增益；經模擬驗證，前者模型可提升±30°的增益並且最高提升6dB，而後者能提升±55°的增益並且最高提升3.4dB；本論文亦對圓柱型的鐵氟龍透鏡在16x4的陣列天線增益效果進行研究，發現其可以在±60°以內達成最低2.2dB，最高3.7dB的增益提升。最後，本論文根據嵌入式單元場型合成理論預測不同激發之合成場型，以此建立成本函式並將擬牛頓法與差分演化演算法引入波束成型優化中，為同時處理主瓣掃描增益、旁瓣波平以及主動式反射係數等多項參數提供一般性的解決方案，結果顯示兩種算法皆可在犧牲增益值0~0.5dB以內、旁瓣波平≈-15dB的情況下，將主動式反射係數降低至少2.3dB。

In recent years, as communication technology enters the 5G era, higher frequency bands are used in communication systems, which brings higher path loss and also has the benefits of increased channel capacity and reduced antenna size; therefore, active array antennas that compensate for gain through multiple antenna elements can be used in commercial applications. This paper develops a dual-polarization 8x8 transceiver array antenna with lens in the millimeter wave band, cooperating with beamforming optimization technology based on differential evolution algorithm, and its operating frequency band is 26.5GHz-29.5GHz. Regarding the array antenna, this thesis completed the design of the 8x8 millimeter-wave array antenna, with good impedance matching, using the beamforming chip of Renesas Electronics. The active array antenna, up/down-frequency module, power supply and control chip are integrated on a single ten-layer circuit board, which helps to improve product stability and reduce the difficulty of later integration with the lens. However, due to product production schedule issues, this paper cannot yet present the measurement results of the array antenna. In terms of lenses, two approximate spherical and cylindrical Teflon lens structures with 8x8 array antennas are proposed. The structure is simple but can effectively improve the gain of the active array at part of the scanning angle; the simulation verification shows that the former model can increase the gain in the range of ±30° and the maximum increase is 6dB, while the latter can increase the gain in the range of ±55° and the maximum increase is 3.4dB. This paper also studies the gain effect of the cylindrical Teflon lens on the 4x16 array antenna, and finding that the gain can increase between 2.2dB to 3.7dB within the range of ±60°. Finally, this paper predicts the synthesized field patterns of different excitations based on embedded element pattern theory, and then establishes the cost function and introduces the quasi-Newton and differential evolution algorithm into the beamforming optimization to provide a general solution for processing multiple parameters such as the main lobe scanning gain, sidelobe level, and active reflection coefficient in the same time. The results show that both algorithms can reduce the active reflection coefficient by at least 2.3dB while sacrificing the gain value within 0~0.5dB with the sidelobe level≈-15dB.