Abstract: A Butler matrix circuit includes: a phase shifter that shifts the phase of a signal, the width of the phase shifter and/or the density of a dielectric material in the phase shifter being set so that the characteristic impedance of the lowest-order mode in the phase shifter varies in accordance with a predetermined function; and a coupler that divides a signal or crosses signals, the density of a dielectric material in a coupled portion between a first waveguide and a second waveguide arranged in parallel being varied in the coupler.

Abstract: In a waveguide, density of a dielectric material in the waveguide is set so that a characteristic impedance of a lowest-order mode in the waveguide varies in accordance with a predetermined function.

Abstract: In a waveguide, a width of the waveguide is set so that a characteristic impedance of a lowest-order mode in the waveguide varies in accordance with a predetermined function.

Abstract: A transmission device includes: a multiplex circular array antenna including a plurality of circular array antennas in which a plurality of antenna elements are arranged in a circle; a plurality of Butler circuits connected to the multiplex circular array antenna; and one or more Butler circuits connected to one or more linear array antennas including some antenna elements among the plurality of antenna elements of the multiplex circular array antenna.

Abstract: A reception device includes a first antenna, a second antenna, and a control unit that combines signals of a radio wave in a first orbital angular momentum (OAM) mode and a radio wave in a second OAM mode having a sign only that is different from a sign of the first OAM mode, received by the first antenna, with signals obtained by rotating OAM phases of the radio wave in the first OAM mode and the radio wave in the second OAM mode received by the second antenna by a predetermined angle to extract a signal of the radio wave in the first OAM mode, and combines signals of the radio wave in the first OAM mode and the radio wave in the second OAM mode received by the second antenna with signals obtained by rotating OAM phases of the radio wave in the first OAM mode and the radio wave in the second OAM mode received by the first antenna by the predetermined angle to extract a signal of the radio wave in the second OAM mode.