HFSS的求解模式

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HFSS的求解模式上一篇 / 下一篇  2008-04-28 23:25:27 / 個(gè)人分類：微波仿真
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HFSS book給出的對(duì)幾種模式的解釋:
Choose the Driven Modal solution type when you want HFSS to calculate the modal-based S-parameters of passive, high-frequency structures such as microstrips, waveguides, and transmission lines. The S-matrix solutions will be expressed in terms of the incident and reflected powers of waveguide modes.
Driven Terminal Solution
Choose the Driven Terminal solution type when you want HFSS to calculate the terminal-based S-parameters of multi-conductor transmission line ports. The S-matrix solutions will be expressed in terms of terminal voltages and currents.
Eigenmode Solution
Choose the Eigenmode solution type to calculate the eigenmodes, or resonances, of a structure. The Eigenmode solver finds the resonant frequencies of the structure and the fields at those resonant frequencies.
關(guān)于driven modal與driven terminal的理解

1.
driven modal
模式驅(qū)動(dòng),所謂模式驅(qū)動(dòng)就是hfss根據(jù)用戶所定義的模式數(shù)目求解端口模式數(shù)目及場(chǎng)分布,并為每個(gè)模式分配相等的功率,仿真時(shí)用端口場(chǎng)分布做為邊界條件對(duì)內(nèi)部進(jìn)行求解,默認(rèn)端口阻抗為Zpi無須定義積分線來求解電壓, S參量用入射反射功率來表示
2.
對(duì)于分析偶合傳輸線等一個(gè)端口上有多個(gè)終端,而求解終端之間偶合問題的模型,driven modal是不適合的.應(yīng)用driven terminal ,這里以微帶偶合傳輸線為例子說明這個(gè)問題




在這個(gè)端口上tem波有兩種模式1.偶模:V1=V2
2.奇模. V1=-V2
(V1為導(dǎo)體1對(duì)接地板等效電壓, V2為導(dǎo)體2對(duì)接地板等效電壓)
如果用driven modal求結(jié)則這兩種模式分別被賦予相等功率,而求解出的S11則是整個(gè)端口上的每一種模式的反射情況,而不能直接求出兩線的偶合狀況(例如只激勵(lì)導(dǎo)體1,求導(dǎo)體2上的端口電壓)這顯然是不合適的.

(關(guān)于偶合傳輸線問題詳情見microwave engineering
edition 3
7.6節(jié))

Driven terminal默認(rèn)的求解終端阻抗為Zvi
故對(duì)于每個(gè)終端需要定義積分線,例如上圖中terminal的積分線為從接地版到導(dǎo)體1的連線(導(dǎo)體1,接地版都為等勢(shì)體,路徑?jīng)]有關(guān)系),terminal2的積分線為接地版到導(dǎo)體2)
計(jì)算機(jī)求解時(shí)對(duì)兩個(gè)終端分別進(jìn)行激勵(lì),通過電壓與電流來計(jì)算他們之間的偶合關(guān)系.

3總結(jié)
1.
如果模型中有類似于偶合傳輸線求偶合問題的模型一定要用driven terminal求解,
2.
driven modal適于其他模型,但一般tem模式(同軸,微帶等)傳輸?shù)膯谓K端模型一般用driven terminal分析(tem波電壓一般由兩導(dǎo)體之間電場(chǎng)積分定義,電流為環(huán)線磁場(chǎng)的積分,阻抗Zvi=Zpi=Zpv區(qū)別于TE TM)由于其直接對(duì)電流電壓求解而避免了對(duì)整個(gè)面上功率的計(jì)算從而比較簡(jiǎn)便.