Abstract
摘要國立清華大學自行設計製造的寬頻帶磁旋行波放大器可產生高功率毫米電磁波。在高效率，高輸出功率及穩定操作之要求下，所得最高輸出功率為18.4KW，效率為18.6％，及18dB增益。在一般的操作條件下，飽合瞬間頻寬在10％以上。除磁旋行波放大器之小訊號特性及飽合特性外，更觀察到一種有趣的模競爭以及模壓抑現象。在不同的操作條件下，用毫米波干射儀所量得一振盪訊號之頻率在55.6?56GHz之間，經確認為二次階波絕對不穩定性所引起之TE21模振盪。用乾熱量計量得之功率約為１KW。 在低輸入功率時，振盪訊號與放大訊號同時存在，增加輸入功率會降低振盪訊號功率。當效大器之輸入訊號大到某一程度時，振盪訊號完全被壓抑。同時，放大訊號之輸出功率突然增加。利用非線性理論計算出飽合輸出功率和實驗值相當吻合。表示當振洫被壓抑後，飽合輸出功率不受振盪之影響。本論文研究之內容包括：□製造一毫米波干射儀量測上述振盪之自由空間波長，並確認為二次階波絕對不穩定性所引起之TE21模振盪。□利用乾熱量計，量測此振盪訊號之功率。□量測輸出功率及振盪訊號功率與輸入功率之關係。□在振盪被壓抑後，飽合輸出功率和理論計算比較，大致吻合。□量測本放大器在不同頻率下之訊號增益，和理論預估值相當吻合。上述之研究結果對於磁旋行波放大器之特性了解以及對以後設計新式的磁旋行╲波放大器有很大的幫助。///////ABSTRACTAn wide band millimeter-wave gyrotron traveling-wave tube amplifier havebeen built and tested in National Tsing Hua University. The operationconditions is optimized for reasonable bandwidth, high efficiency, highoutput power and good stability, 18.4 kW output power is obtained at18.6% efficiency and ?18 dB gain. More than 10% saturated instantaneousbandwidth (FWHM) is typical for various operation conditions. Theperformance of the tube including small signal and saturatedcharacteristics were investigated. Also, oscillations with frequencies inthe range 55.5?56 GHz was observed to cause mode competition in thisamplifier. It was found that these oscillations can be suppressed by drivepower.This thesis is relevant to the above studies. A millimeter-waveFabry-Perot interferometer was constructed to measure the free spacewavelengths of the competing mode. It was identiffied to be the secondharmonics absolute instability in TE21 mode. The power of the oscillationsare of order of 1 kW as measured by dry calorimeter. The relation betweenthe amplified output power and the relateve oscillation power are alsomeasured. In the low drive power region, the oscillation and theamplifying wave co-exist, the measured P out versus P in is differentfrom a conventional linear curve in small signal region. Increasing thedrive power would reduce the power of oscillation. When the drive power isincreased to certain value, the oscillation can be suppressed completelyand the amplified output power increased significantly. When theoscillations is suppressed, the saturated output power agrees with thetheoretical predictions. At the optimized operation condition, smallsignal gain, saturated output power and saturated gain at differentfrequencies were measured. Comparsion between theories and experimentaldata were made. This predictability allows us to consider more advancedschemes such as two stages gyro-TWT to improve gain and magnetic fieldprofiling to enhance efficiency.