方槽天线轴比带宽

找了一些圆极化方槽天线的文章，轴比带宽都非常宽，原理是什么，求大神解答。

如这篇文章Broadband CPW-Fed Circularly Polarized Square
Slot Antenna With Lightening-Shaped Feedline and
Inverted-L Grounded Strips

[attachment=65379]如这篇文章Broadband CPW-Fed Circularly Polarized Square
Slot Antenna With Lightening-Shaped Feedline and
Inverted-L Grounded Strips

不要沉不要沉不要沉