Communication system and filter thereof

The invention discloses a communication system and a filter thereof. The filter comprises: a first filtering branch composed of eleven filtering cavities which are coupled in sequence, wherein the eleven filtering cavities of the first filtering branch further form three cross coupling zero points; a second filtering branch composed of eleven filtering cavities which are coupled in sequence, wherein the eleven filtering cavities of the second filtering branch further form three cross coupling zero points; and a third filtering branch composed of eight filtering cavities which are sequentially coupled, wherein the eight filtering cavities of the third filtering branch further form three cross coupling zero points, and the fourth filtering branch and the third filtering branch are symmetrically arranged. The first to sixth filtering cavities of the first filtering branch are the same as the first to sixth filtering cavities of the second filtering branch in structure; and through the mode, the filter cavities a