平衡式濾波器(balanced filter)因其對稱架構，擁有不需要打連通柱(via)到接地端與對雜訊擁有高免疫力的優點。為了得到操作在差模(differential-mode)狀態下的散射參數(S-parameter)，利用傳統單端(single-ended)散射參數與混模(mixed-mode)散射參數之間的數學轉換關係，可以將純模(pure-mode)與模態轉換(mode-conversion)的散射參數順利推導出來。由於雙埠向量網路網路分析儀(vector network analyzer, VNA)無法直接量測差模電路，本論文設計並實做出鼠競式(rat-race)與馬群(Marchand)兩種巴倫(balanced-to-unbalanced, balun)分波器來產生差模訊號，在電路兩端分別接上巴倫的平衡埠，非平衡埠與網路分析儀兩端埠相連，如此一來即可直接觀察差模的通帶響應。另一種理想巴倫為利用中央抽頭式(center-tapped)變壓器來產生差模與偶模訊號的混模散射參數轉換電路，又稱為魔術-T(magic-T)，其結果會與上述數學轉換結果一致。非理想巴倫由於電路板製造所產生的不均勻，其實作電路在傳輸時會有模態轉換的情形發生，造成量測結果與模擬之間的誤差，因此最終的測量結果並非純粹的差模響應。
本論文提出用半波長(λ/2)步階性阻抗共振器(stepped-impedance resonator, SIR)組成的四階平衡式帶通濾波器，由於架構的對稱性，我們可將其從對稱中線剖半，直接分析半電路。相對於半波長共振器，四分之波長共振器的第2次共振位於較高的3倍基頻，再加上利用步階性阻抗共振器可藉由調整不同線段的高低阻抗比與電氣長度比，將高階諧波推往比均勻阻抗共振器(uniform-impedance resonator, UIR)所能達到得更高頻的位置。接線餽入(taped-line feeding)可以節省空間與成本，並且在截止帶產生額外的傳輸零點(transmission zero)，實作電路具有良好的差模截止帶表現至3.59倍基頻，而共模可壓至4.13倍基頻。為了更進一步壓低贅餘通帶(spurious passband)，並減少設計共振頻率上的複雜度，選擇將步階式與均勻式阻抗共振器搭配使用，結構上有電容性與電感性耦合的混合效果而產生零點，以此增加選擇度與壓縮贅餘響應(spurious response)，實驗結果可將差模截止帶壓低至13.1倍基頻處，而共模可壓至9.8倍基頻處。兩種濾波器均有緊密的尺寸。

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