Ku-頻帶平衡式功率放大器使用直流阻絕耦合式阻抗轉換分歧耦合器

Abstract

摘要 本論文提出一種改良型微帶線阻抗轉換分歧器用於Ku頻帶(14.4 ~14.6GHz)窄頻平衡式功 率放大器. 此分歧耦合器利用平行耦合線取代 原有的四條分支線, 適當的調整平行耦合線之奇偶阻抗以達到所需之低阻 抗; 利用其本身既有的開路特性以達到四個埠之間的直流隔絕.這不但改 善傳統分歧耦合器的Ｔ型不連續接面在高頻所激發之高次模電磁場效應, 進而降低了模擬與實驗的誤差率, 相對地電路面積也減少許多. 此外, 利 用阻抗轉換分歧耦合器的阻抗轉換特性, 以降低功率電晶體所需之阻抗轉 換匹配比率, 則匹配電路可予於簡化, 以避免匹配造成之功率損耗, 並且 功率放大器整體電路面積更小, 密度更高, 更適合MMIC化. 此外, 為 了將來邁向MMIC化, 我們規化了一套完整的Chip MESFET和MHEMT小訊號模 型的粹取流程, 以簡單的小訊號模型近似出等效大訊號輸出模型, 適用於 功率放大器的設計; 其中包括用於準確小訊號Ｓ參數量測時所採用之TRL De-embedding方法, 都全部將予以程式模組化. Abstract In this project, we demonstrate a modified Ku-band microstrip line impedance -transforming branch-line coupler used for a narrowband balanced power amplifier. In this new coupler design, the original four branches of the coupler are replaced by coupled-lines, and the coupled-lines can be chosen carefully to obtain the necessary low impedance, and use the inherent open characteristic to get the DC-isolations between the four ports. This design not only suppr進而esses the high order-mode excitations, which result from the discontinui supreesses T- junctions at high frequencies, it can also make the simulation mties of and the relative size of the circuit reduced. In additions, impedance- tdesign, the overall amplifier circuit area are smaller, high density, and more suitable for MMIC design. In additions, in this project, we program a design procedure for the small-signal model extraction of chip-form MESFET and HEMT. An equivalent large-signal model using the small-signal parameters is derived, and included in the power amplifier design. In this project, the TRL de-embedding method is also discussed for the accuracy measurement of small-signal S-parameters.