45度線性極化高增益毫米波微帶天線陣列

Abstract

本論文提出一應用於77 GHz車用前視防撞警示雷達長距模態之45度線性極化天線陣列。長距模態雷達目的在偵測本車道前方車輛與本車之距離和速度，操作頻段為76 GHz到77 GHz。45度線性極化之特性可使本車與對向來車所用之雷達天線極化正交，避免收到其雷達波干擾而降低偵測率。本設計採用微帶天線作為輻射單元，具有體積小、厚度薄、成本低、製造容易，以及易與電路整合之優點。此天線陣列為雙層基板結構，將天線與電路分開，以避免電路對天線場型的影響。電路層使用微帶線，經由兩反向連通柱(via)從陣列中央饋入天線，增加輻射場型的頻寬。在天線層，使用天線耦合器作為各個子陣列間的功率分配，簡化電路層之走線複雜度。本設計之模擬、實作，與量測資料皆載於本文中。天線整體尺寸為68mm*14mm*0.7mm，具有高增益、窄波束、低旁波束等級(sidelobe level)，以及低交叉極化等級(cross-polarization level)等特性。

In this thesis, a novel 45-degree linear polarized antenna array for 77GHz vehicle collision avoidance warning long-range radar (LRR) is proposed. The LRR is used to detect the distance and velocity between the vehicles in front and it, of which the operation band is from 76 GHz to 77 GHz. The antenna polarization is 45-degree slant in order to be orthogonal to the radar signals from vehicles on the opposite side. Therefore, this prevents from lowering the detection accuracy. Microstrip patch antenna is chosen as the radiating element, which is low profile, low cost, easy fabrication, and easy integration. In this structure, there are two substrates with three metal layers which, from top to bottom, are antenna layer, ground, and transmission line layer, respectively. The transmission line layer is separated from the antenna layer in order not to affect the radiation pattern. Two out-of-phase vias at the center element are used as the antenna feed, which prevents the antenna beam tilt, and hence increases the bandwidth of the radiation pattern. In the antenna layer, antenna couplers are used to distribute power to each sub-array. This reduces the complexity in the transmission line layer. The simulation, fabrication, and measurement of this design are presented in this thesis. The proposed antenna is high-gain, narrow-beamwidth, low-sidelobe-level, and low-cross-polarization-level, with overall size 68 mm*14 mm*0.7 mm.