To make it possible to obtain a compact equipment by making the interval between neighboring antenna elements of transmitting antenna system and receiving antenna system as small as possible within the range obstructing the state of radio wave interrupting plates arranged at certain intervals regardless of the wavelength of the radio wave used.

Antenna element a and radio wave interrupting plate b are alternately arranged in plurality thereby creating a transmitting antenna system and a receiving antenna system, and the surfaces of respective antenna elements arranged are faced each other at a certain distance (r) provided between them. This distance (r) is desired to be as small as possible. However, if it is smaller than one-half of the wavelength, they are affected by induction wave and electrostatic wave. More electric power of the receiving antenna is given from the transmitting antenna instead of spatial energy, and this situation is not desirable. A distance equal to two wavelengths is appropriate. By doing this, a compact equipment can be obtained.