Demonstration of a Degenerate Band Edge in Periodically-Loaded Circular Waveguides

TL;DR

This paper demonstrates the existence of a degenerate band edge (DBE) in periodically loaded circular waveguides at microwave frequencies, revealing new resonance properties and potential applications in amplifiers and pulse compression.

Contribution

First demonstration of DBE in hollow circular waveguides using simple periodic loading structures, expanding understanding of waveguide resonance phenomena.

Findings

DBE observed in two different periodic waveguide structures

Conditions for DBE derived using a multi transmission line approach

Potential applications in traveling wave tubes and pulse compressors

Abstract

We demonstrate the existence of a special degeneracy condition, called degenerate band edge (DBE), between two Bloch modes in periodically loaded circular all-metallic waveguides at microwave frequencies. The DBE condition has been associated with a dramatic reduction in group velocity and with some unique resonance properties, but it has not been shown in hollow waveguide structures yet. Hence, we show here its existence in two periodic waveguide examples. The unit cell of the first case is composed of a circular waveguide loaded with two inner cylinders with elliptical irises with misaligned angles. The second structure is composed of loading the waveguide with elliptical rings. The demonstration of DBE in those waveguide is explained through a simple multi transmission line approach where the conditions to obtain DBE are clarified, and suggests that the DBE can occur in several other analogous periodic waveguide. These structures can be potentially used to investigate unconventional gain schemes in traveling wave tubes or other kinds of distributed amplifiers and novel pulse compressors.