金属周期加载圆波导中简并带边的实验验证
Experimental Demonstration of Degenerate Band Edge in Metallic Periodically-Loaded Circular Waveguide
摘要：
首次从实验上证明了加载金属圆波导中的简并带边条件，即四个布洛赫模的简并。形成DBE的四个模式表示发生在周期性结构中的四阶简并，其中四个布洛赫模式（两个传播模式和两个消逝模式）合并。它导致非常平坦的波数-频率色散关系，并且有限长度结构的品质因数按比例缩放为$N^5$，其中$N$是单位单元的数量。建议的波导中观察DBE在这里是通过周期性加载的圆波导与不对齐的椭圆形金属环，由低折射率电介质的支持。我们验证了存在的DBE在这样的结构中使用测量，我们报告的全波模拟和测得的响应的波导附近的DBE频率之间的良好的协议;考虑到金属损耗。我们利用各种技术，包括色散合成，以及观察如何品质因数和群延迟规模的结构长度的增加，我们的发现相关的理论和模拟结果。此外，所报道的几何形状仅是具有DBE的金属波导的示例：DBE并且其特性也可以被设计在许多其他种类的波导中，并且各种应用可以被设想为基于电子束相互作用的放大器和振荡器中的高微波生成或固态器件、脉冲压缩器和微波传感器。
英文摘要：
We experimentally demonstrate for the first time the degenerate band edge (DBE) condition, namely the degeneracy of four Bloch modes, in loaded circular metallic waveguides. The four modes forming the DBE represent a degeneracy of fourth order occurring in a periodic structure where four Bloch modes, two propagating and two evanescent, coalesce. It leads to a very flat wavenumber-frequency dispersion relation, and the finite length structure's quality factor scales as $N^5$ where $N$ is the number of unit cells. The proposed waveguide in which DBE is observed here is designed by periodically loading a circular waveguide with misaligned elliptical metallic rings, supported by a low-index dielectric. We validate the existence of the DBE in such structure using measurements and we report good agreement between full-wave simulation and the measured response of the waveguide near the DBE frequency; taking into account metallic losses. We correlate our finding to theoretical and simulation results utilizing various techniques including dispersion synthesis, as well as observing how quality factor and group delay scale as the structure length increases. Moreover, the reported geometry is only an example of metallic waveguide with DBE: DBE and its characteristics can also be designed in many other kinds of waveguides and various applications can be contemplated as high microwave generation in amplifiers and oscillators based on an electron beam interaction or solid state devices, pulse compressors and microwave sensors.
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