An unbalanced microstrip bandpass filter (BPF) in dual-extended doublet topology with source-load (S-L) coupling is first presented and researched based on dual-layer capacitive-loaded dual-mode loop resonators. The input and output ports are located on the upper substrate layer. The lower dual-mode loop resonator is coupled to the upper loop resonator using four coupling apertures in the middle metal layer. Single- and dual-band responses with four controllable finite-transmission zeros (FTZs) are analysed. Then, a balanced BPF in dual-extended doublet topology without S-L coupling on the basics of the proposed unbalanced filter is presented and researched. Single- and dual-band differential mode responses with three controllable FTZs can be realised with good common mode suppression. Some design examples are provided to illustrate the performances of the realised single- and dual-band unbalanced and balanced filters with controllable FTZs. The measured results agree well with simulated ones.

中文翻译：

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紧凑的单带和双带带通滤波器，使用双层双模式环路谐振器可控制传输零点

基于双层电容负载双模环路谐振器，首次提出并研究了具有源-负载（SL）耦合的双扩展双峰拓扑中的不平衡微带带通滤波器（BPF）。输入和输出端口位于上基板层上。下部双模式环形谐振器使用中间金属层中的四个耦合孔耦合到上部环形谐振器。分析了具有四个可控有限传输零点（FTZ）的单频带和双频带响应。然后，在所提出的不平衡滤波器的基础上，提出并研究了双扩展双峰拓扑中没有SL耦合的平衡BPF。具有三个可控FTZ的单频带和双频带差分模式响应可以通过良好的共模抑制来实现。提供了一些设计示例，以说明实现的具有可控FTZ的单频带和双频带不平衡和平衡滤波器的性能。测量结果与模拟结果吻合良好。