微波準光學高功率混成場效應電晶體方柵陣列振盪器

Abstract

本論文是設計, 製作, 測量一個高功率的準光學方柵結構之振盪器, 此 振盪器由 16 顆 MESFET 形成的陣列加上一個反射鏡所組成.通常在高 頻情況下, 一般固態元件無法達到高功率, 因此有必要組合較多的元件 以得到渴望的高功率.本設計是參照加州理工學院 Prof.Rutledge 對 grid oscillator所做的研究. 在設計過程中, 發現方柵的線寬, 週期, 基板的材質都會影響振盪器的行為, 因此首先了解方柵結構電磁效應, 並 將其轉成為一個被動等效電路. 組合方柵結構傳輸線模型及電晶體模 型, 以 Libra模擬之, 當反射鏡離方柵 137mil, 預估振盪頻率約為 4.1GHz.在製作時, 由於方柵結構的高對稱性要求, 我們測量了 50 顆電 晶體的特性, 找出其中 16 顆性質接近的電晶體, 作為電路的主動元件. 並使用介電質常數為 10.5, 厚度 100mil 的 duroid 為基板, 加上偏壓 線, 完成振盪器.整個測量結構建立在光學板上, 每個 FET 偏壓 在 Vds=3V, Id=12.5mA 下, 當反射鏡距方柵 3.5mm, 方柵離接收天線 22cm, 產生的訊號經由頻譜分析儀量測, 獲得振盪頻率為 4.0GHz, 接 收功率為 7.66dBm, 幅射功率超過 150mW, 諧波失真小於 -35dBc. 若使用 monolithic technique, 可以得到更大的功率. Solid-state devices can not generate large power at very high frequency,it is necessary to combine many solid-state devices to obtain high power. In the thesis, the quasi-optical high power hybrid MESFET grid array oscillator is designed. The fabrication and measurement are also present. The project is based on the circuit designed by Prof. Rutledge's group in California Institute of Technology. The frequency of oscillator is determined by the period and the lead width of grid, and the substrate used. Therfore, it is necessary to study the electromagnetic field in the grid and obtain the equivalent circuit. The equivalent circuit of oscillator is simulated by Libra. When bias at Vds=3 V, Vgs=-0.9V, Fabry-Perot mirror locate at the back of grid at about 3.5mm, the oscillation frequency is measured to 4.1GHz. Because the grid require high symmetry, we sampled 50 MESFET to find 16 FET with similar quality. The duroid has a dielectric constant of 10.5, and the thickness is 100mil. The oscillator is formed by combining 16MESFET in Fabry-Perot cavity. The distance between horn and grid is 22cm. Using the spectrum analyzer, at Vds=3V, Id=12.5mA, the oscillation frequency is measured at 4.0GHz. The power received by spctrum analyzer is 7.66dBm, it is about more than 150mW. The harmonic distortion is less -35dBc. If use the monolithic technique, it will generate much more power.