應用於具可切換波束及可重塑場型合成孔徑雷達系統之反射式天線饋源陣列

Abstract

本論文提出應用於X-band頻段（9.30 GHz ~ 9.60 GHz）星載合成孔徑雷達之酬載天線——反射式天線——饋源陣列設計。在衛星構型與反射面尺寸確定後，設計出一適合於此反射面尺寸的雙極化（水平極化與垂直極化）饋源陣列，其共有六只饋源單元，以兩相鄰饋源單元為一波束的饋源，可使酬載天線達成五個不同指向的波束。 以「空間功率合成」概念規劃此多饋源單系統架構，每一饋源單元線路上均搭配一高功率放大器，使得饋源單元組合能不受限制，增加了不同特性的天線波束。在運用這些不同指向與不同寬度的波束下，靈活和復雜的成像模式操作（普通Stripmap模式，寬Stripmap模式，ScanSAR模式和Spotlight模式）得以實現。 饋源單元選擇以號角天線的形式設計。透過在號角天線開口處安置一十字結構，以較小的號角天線孔徑達到訂定的波束寬目標，藉此縮小作為饋源組合的相鄰饋源單元間距，使在饋源場型塑造更容易達成。利用完成設計的號角天線饋源陣列分析酬載天線其天線指向性、波束寬與可掃描角度等特性；此外，藉由其實作量測結果與相關元件資料，估算系統架構輸入端與輸出端的訊號隔離度。

In this thesis, an X-band antenna feed-array of reflector antenna for satellite SAR system is presented. After the construction of the satellite and the size of the reflector are confirmed, the dual polarizations feed-array, which composes 6 elements, is designed to fit the reflector. With two adjacent feed elements as a beam of feed, the payload antenna can be reached five beams in different directions. The multiple feeds system in conjunction with the distributed PA modules, not only performs the spatial power combining for radar detection, but also provides the beam diversity. Flexible and complex imaging mode operations (normal Stripmap mode, broad Stripmap mode, ScanSAR modes and Spotlight mode) become realistic with these multiple beams having various directions and various widths. The feed unit is in the form of horn antenna. By placing a cross structure at the opening of the horn antenna, the goal of the specified beamwidth is reached with a smaller aperture, thereby reducing the spacing of adjacent feed elements as feed combinations to make it easier to shape the feed fields. The biased angle, beamwidth and sweep angle of the payload antenna are analyzed by the designed feed-array. In addition, the T/R isolation of system is estimated by its actual measurement results and related components.