This letter presents an analytical procedure for the synthesis of a low-pass prototype filter constituted by the cascade of doublet blocks coupled by inverters or shunt reactances. The considered doublet is a second-order resonating structure composed of two resonant and two nonresonant nodes which allow the placement of two finite transmission zeros (TZs) in the frequency response. The considered configuration allows realizing compact fully canonical filters with the maximum number of TZs (the doublets are typically implemented through dual-mode cavities). The proposed procedure introduces for the first time an analytical procedure for synthesizing the low-pass prototype of the cascaded-block topology, overcoming the time consuming and inaccurate procedures currently based on numerical optimization. Two synthesis examples are presented to validate the novel synthesis procedure.

中文翻译：

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全规范级联双原型滤波器的分析综合

这封信提出了合成低通原型滤波器的分析程序，该滤波器由由逆变器或并联电抗耦合的双联块级联构成。所考虑的双峰是由两个谐振节点和两个非谐振节点组成的二阶谐振结构，允许在频率响应中放置两个有限传输零点 (TZ)。所考虑的配置允许实现具有最大 TZ 数量的紧凑型完全规范滤波器（双峰通常通过双模腔实现）。所提出的程序首次引入了用于合成级联块拓扑的低通原型的分析程序，克服了目前基于数值优化的耗时和不准确的程序。