Polarization coupler

A polarization coupler comprising:

• a circular waveguide;
• a quadrangular waveguide that is arranged in an axial direction of the circular waveguide, and has a short side shorter than an inner diameter of the circular waveguide;
• a connector waveguide that connects the quadrangular waveguide with the circular waveguide;
• a flat conductor wall that is formed over the connector waveguide and the circular waveguide, and divides the inside of the connector waveguide and the circular waveguide arranged parallel to a direction where a long side of the quadrangular waveguide extends;
• a first inclined surface that is formed on an inner wall of the connector waveguide at a position facing one surface of the conductor wall, and inclined toward the conductor wall as coming closer to the quadrangular waveguide;
• a second inclined surface that is formed on the inner wall of the connector waveguide at a position facing the other surface of the conductor wall, and inclined toward the conductor wall as coming closer to the quadrangular waveguide;
• and
• a coupling hole that is formed in the circular waveguide, and extracts one that is polarization-divided by the conductor wall out of electromagnetic waves propagated through the circular waveguide,
• wherein the connector waveguide is configured by:
• an arc-shaped first wall surface;
• an arc-shaped second wall surface that faces the first wall surface;
• the first inclined surface;
• and the second inclined surface.