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Space-Time Modulated Electromagnetic Signals
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Space-Time Modulated Electromagnetic Signals

The development of advanced electronic hardware increases the interest in space-time modulation. Such signals carry the digital [1] or analogue [2] information by their amplitudes and the space distribution of the field. In electromagnetics, the space-time radiation is from distributed antennas and due to the reflections from natural or artificial structures whose size is comparable with the wavelength. Microwave optics now is in a high demand to visualize the objects which are in the outer space or inside the human body or solid matter. The use of spatially modulated signals for telecommunication started to be considered only at the end of last century [3] in spite a theory of such signals was developed many years ago [2],[4]. All considered applications are based on the fact that the space-time signals are originated from distributed antennas consisting of multiple elements. A spatial coding of the radiated signals allows increasing the noise immunity and the speed of the wireless telecommunications [ 3].

In the beginning of 90s, a new idea on space-time modulation was proposed [1],[4]-[8]. It was shown that the electromagnetic waves can be spatially-modulated even inside the tiny integrated circuits (IC). In this case, the spatial period of the electromagnetic signals is set up by the distance between tightly coupled microstrip conductors. Thus, the density of spatial information is defined by the lithography, and the spatial frequency band of signals is comparable with several Gigahertz per millimeter. The main carrier of spatial information is the topological chart of the electromagnetic signals. This chart is an arranged set of equilibrium points and separatrices of the field force line pictures. This chart or topological scheme is changed only abruptly, and it is for digital signaling (Fig. 1)