單脈衝衛星追蹤地面站天線饋入器設計

Abstract

本論文提出一個應用在S band的單脈衝地面站自動追蹤天線饋入器，發射頻段為2.025到2.12 GHz，接收頻段為2.2到2.3 GHz，此饋入器具有修正天線方位角度的功能，使天線boresight方向可以對準衛星進行通訊。根據單脈衝追蹤雷達的原理，此系統架構可以分為sum 和difference channel兩部分來探討。Sum channel部分主要用於作資料傳輸，主要的元件為產生圓極化電場的步階隔板極化器，考量體積縮小化，非採用傳統OMT結構，difference channel的部分則是用做修正角度，主要元件為TE21模態耦合器，波導管內的最高模態為TE21。在polarizer與模態耦合器之間為linear taper結構，有抑制高階模態的作用。由模擬結果，此饋入器的VSWR小於等於1.5。透過公式計算，極化隔離度大於20 dB，可知boresight方向軸比值小於1.5 dB。

An S-band auto-tracking antenna feed for mono-pulse ground station is presented. The uplink band is from 2.025 to 2.12 GHz and the downlink one is from 2.2 to 2.3 GHz. The feed is utilized to modify the orientation angle of the antenna to align antenna boresight with a satellite. According to the mono-pulse radar theory, the system structure can be divided into two parts of sum and difference channels. The part of sum channel is used for data transmission and the key component is a septum polarizer which generates circular polarized electric fields. For the miniature purpose, we choose a septum polarizer instead of OMT structures. The other part of difference channel is used for modifying the angle and the key component is a TE21 tracking coupler with the highest mode, TE21 mode. Between the septum polarizer and the tracking coupler, there is a taper structure for suppressing unwanted higher order modes passing down to the polarizer. The simulated results show that the VSWR is below 1.5. The calculated results show the polarization isolation is larger than 20 dB, and the axial ratio is smaller than 1.5 dB in boresight direction.