應用於77GHz車用防撞警示雷達系統之45度線性極化高增益低旁波束微帶天線陣列

Abstract

本論文提出一組應用於77GHz車用前視防撞警示雙模雷達之45度線性極化長距與短距天線設計。其中長距天線操作頻段在76GHz到77GHz，具有高增益、窄波束以及低旁波束等特性，用以提供本車道前方遠距離偵測；短距天線操作頻段為77GHz到81GHz，具有寬波束，低旁波束等特性，可提供近距離大範圍角度偵測。兩天線之基本架構皆為陣列天線，為了節省整體系統的面積而設計在雙層基板的架構下，使電路和天線能上下分層，因此饋入方式採用穿層饋入，並設計縮小化反相位饋入結構，更進一步節省空間，並選擇饋入點於天線陣列中央，使波束較不易隨頻率偏移。 另外本論文同時也提出一毫米波量測治具，有鑑於在此頻段所使用的儀器其埠介面大多為波導管型式，而平面天線饋入方式多為微帶線型式，故設計一低損耗、高重複性、高準確度的波導管至微帶線的轉換結構，並以此結構進行天線的量測。

In this thesis, two 45 degree linearly polarized antennas which are applied in a dual-mode vehicular collision warning radar system are designed and measured. The two modes in this system are Long Range Mode(LRM) and Short Range Mode(SRM). The operating frequency of LRM is from 76GHz to 77GHz, and its main purpose is to detect long-range targets within the same lane, hence antennas designed for this mode are highly directional, narrow beamwidth and preferably low side lobe level. While the operating frequency of SRM is from 77GHz to 81GHz, and is set to detect targets at closer range and/or larger angle, therefore antennas designed for this mode have wider beamwidth. Both of the antennas presented in this thesis are microstrip antenna array designed in a double-layer structure with antenna and RF front end circuit situated on top and bottom layer respectively. The antennas are fed at the phase center by a compact feeding structure using plated through hole. Considering that measuring instruments at this frequency band commonly use waveguide type port interface, a waveguide to microstrip transition structure and its corresponding fixture is also designed with aim of improving repeatability and reproducibility.