Detection of non-TEM waves in open media
Solutions of Maxwell's equations for directions of interest not coinciding with the direction of propagation of uniform TEM infinite plane waves have been proposed, for the first time by T. Koryu Ishii, in 1952. His theoretical treatment predicts the existence of rapid non-TEM modes of propagation for these directions of interest. By solving Maxwell's equations for uniform TEM spherical waves and by using a transmission line analogy, it is possible to obtain the isosceles cones of propagation of a more general wave. It is shown that radiation observed along the outer cones propagates faster than the observed energy along the inner cones. This radiation can be interpreted as non-TEM modes, at any observation point within the cone. At the early generation stages of these waves, an acceleration process takes place, due to the position dependency of the characteristic impedance of the medium. As a further step a theoretical study was performed on the phase velocity concept, applied in the transmission of digital information. Experiments in open space were performed to verify the above stated theory using space and time domain techniques. In addition, time domain experiments were performed inside a waveguide. The time domain experiments were performed by using the time domain reflectometry technique and measuring the transit time between incident and received pulse amplitude modulated signal. It is concluded that the experimental findings seems to support the theory. A definition of a velocity of the signal which can be identified as the velocity of propagation of the early detectable portion of the leading edge of the wavefront of the microwave pulse is offered. The velocity of the signal is different from the signal velocity concept and is equal to the phase velocity in a free space, which is equal to the intrinsic velocity, the speed of light. However it was found that the radiation emerging from non-TEM modes propagates with a velocity of signal apparently exceeding the speed of light. If this is so, applications in rapid deep-space communications would potentially be possible.
Giakos, George C, "Detection of non-TEM waves in open media" (1991). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI9200157.