Abstract: An inductive radio communication system in which two sets of parallel lines are provided so as to be separated from each other at a predetermined distance therebetween along the track of a mobile unit, and a loop antenna having a double loop structure and attached on the mobile unit is disposed between the two sets of parallel lines. The loop antenna is arranged such that currents flow in the respective loops in opposite directions to each other at a certain instant. Levels of signals transmitted from the loop antenna to the parallel lines through electromagnetic coupling are added to each other when the signal levels are applied to the primary side of a level converting transformer, and then the output of the transformer is transmitted to a receiver of the ground station side, whereby the undesirable noises radiated to the outside is reduced and the coupling level between the antenna and the parallel lines through electromagnetic coupling is improved.

Abstract: At least a set of two spatial filters are so arranged in a two-dimensional space or three-dimensional space that their spatial distributions are opposite to each other. Two systems of light detection signals from a moving object are synchronously collected through the spatial filters, integrated, and photoelectrically converted into time-series electrical signals. The electric signals are processed according to a predetermined algorithm. A result of the process is judged as positive or negative to find the direction of a velocity of the object. The magnitude of the velocity is found from the two systems of light detection signals according to a known equation. Instead of oppositely arranging the spatial distributions of the two spatial filters, at least one differential spatial filter system may be employed to provide light detection signals corresponding to those provided by the oppositely arranged spatial filters.