由等效介質參數萃取法得到的等效折射係數，以及特徵模態分析法得到的色 散關係，可以知道本論文提出的漁網結構，在基礎模態可以視為等效介質，並具 備等效折射係數小於一的特性，其截止頻率為7GHz。並找出此漁網結構的電路 模型，來探討結構參數對頻率的影響，以加速結構的設計，知道對於相同晶格常 數而言，漁網結構中和電場同向的金屬線越窄，造成的並聯電感值越大，使得截 止頻率越低。
利用漁網結構製成四波束的指向性空間波束分歧器，其返回阻抗和輻射場型 的結果，在模擬和實際量測上有相當的一致性。在頻率為7.5GHz，量測的的增 益為8.69dBi。
最後，給出了一個人造介質材料用來設計空間波束分歧器的流程圖。由前面 章節的分析，我們得到分析和設計的方法。對於提出的漁網結構，可以用等效介 質參數萃取法和特徵模態分析法分析，特徵模態分析適合分析單晶格的頻帶結 構。在本設計流程是以金屬網格的等效電路模型來估計漁網結構的截止頻率和色 散關係，再將調整過的結構參數之單晶格，模擬取得S參數，以等效介質參數萃 取法獲得neff和zeff。
將等效係數套用至傳輸線模型，獲得阻抗匹配的頻率和單晶格個數的關係，
決定適當的單晶格個數。最後，以將完整結構模擬，對某些結構參數微調，使在 設計的頻率有良好的阻抗匹配，獲得遠場輻射場型和返回損耗，完成空間波束分 歧器設計。
Metamaterial substrate Cutoff frequencies estimation from
equivalent circuit models Unit-cell transmission simulation
S parameters
Propagation constant and wave impedance
Eigenmode analysis
Impedance matching behavior from circuit models
Determine the number of unit-cell repetitions
Full-wave simulation of the whole structure
Farfield radiation patterns and return loss
Complete band structures
Fine tuning of feeding and radiating aperture
Metamaterial substrate Cutoff frequencies estimation from
equivalent circuit models Unit-cell transmission simulation
S parameters
Propagation constant and wave impedance
Eigenmode analysis
Impedance matching behavior from circuit models
Determine the number of unit-cell repetitions
Full-wave simulation of the whole structure
Farfield radiation patterns and return loss
Complete band structures
Fine tuning of feeding and radiating aperture
圖 5-1 使用人造介質材料設計之空間波束分歧器的設計流程圖
Appendix A
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