Wireless node that uses a circular polarized antenna and a mechanism for preventing corner reflections of an inside of a metal box space

Abstract

In the present invention, upon reflection of an electromagnetic wave on a metallic surface, a phenomenon is employed that the direction of rotation of a circularly polarized wave is reversed for every reflection. By utilizing a circularly-polarized-wave transmitting and receiving antenna to transmit and receive the circularly polarized wave, the polarized wave of the electromagnetic wave after reflected an odd number of times from the metallic surface has its rotating direction reversed with respect to a receivable rotating direction of the transmitting and receiving antenna, thereby reducing noise caused by the odd number of reflections. In other words, the reflected wave from the wireless node for communications or measuring of a distance is set to have its rotating direction rendered identical with a rotating direction of the transmitting and receiving antenna. As a result, a signal-to-noise (S/N) ratio is improved, thus facilitating the communications or the measuring of the distance among the wireless nodes disposed in a metal box such as a container. Generally, in the wireless node set or attached onto an inner wall of the rectangular metal box, the radio wave radiated from the node in a downward direction with respect to a horizontal plane (towards a setting wall) will be reflected twice by a corner reflection phenomenon in the vicinity of the corner of the box, and then return to the original wireless node in most cases. The wireless node of the present invention is designed to have its directivity which does not spread in an area under the horizontal plane.