<title>Time-domain detection of a phase velocity</title>

Abstract

The objective of this paper is to present the fact that phase velocity of electromagnetic wave propagation is observable in time domain. Time domain observability of phase velocity in a rectangular waveguide was first reported by Giakos and Ishii in 1991. The validity of their observation was questioned and disputed. The questions were answered by the observers but more confirmation is desirable. This paper presents case history of time domain observed superluminal phase velocity of other authors in the past. The latest work of this author and his colleagues to confirm his earlier observation is also presented. The earliest documented observation of superluminal phase velocity can be found in Snell's law (Snell 1621). According to published time domain data of pico-second electromagnetic pulse propagation of the following cases, superluminal speed propagation of the leading edge of the pulse was observed. In a dispersive transmission system, if observed, differential speed in frequency domain dv/df is negative, the detector is responding to the phase velocity. If dv/df is positive, the detector is responding to the group velocity. This paper presents cases of dv/df negative.