Effect of evanescent modes on the transmission and group delay of a wave

• Published in: 2009 34th International Conference on Infrared, Millimeter, and Terahertz Waves pp. 1 - 2
• Main Authors: Yao, H.Y., Chang, T.H.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.09.2009
• Subjects: Boundary conditions; Cutoff frequency; Delay effects; Electromagnetic scattering; Electromagnetic waveguides; Geometry; Modal analysis; Potential well; Propagation delay; Quantum mechanics
• ISBN: 1424454166; 9781424454167
• ISSN: 2162-2027
• DOI: 10.1109/ICIMW.2009.5325681

The transmission and group delay are investigated for two kinds of waveguide systems. The systems consist of a middle section with distinct cutoff frequency to model the potential barrier or well in quantum mechanics. The cutoff frequency of the middle section is controlled by either the cross-sectional geometry or the properties of loaded material. Modal analysis is introduced because the electromagnetic waves have their own boundary conditions in virtually three-dimensional waveguide systems. The modal analysis is calculated and the results are compared with the simulations using a full wave solver. In the oversized/undersized waveguides case, the calculated results converge quickly as the number of modes of consideration is increased. The higher-order modes which are generally evanescent modify the phase of the fundamental mode and subsequently affect the wave characteristics. The underlying physics is manifested using a multiple-reflection model. This study shows that the evanescent modes are critical for a microwave system with geometrical discontinuity and suggests that it might also play an important role in quantum mechanics.