Directional coupler

A directional coupler comprising:

• a first electrically conductive member having a first electrically conductive surface;
• a second electrically conductive member having a second electrically conductive surface opposing the first electrically conductive surface;
• a plurality of ridges protruding from the second electrically conductive surface, each having an electrically-conductive waveguide face which extends in opposition to the first electrically conductive surface;
• and
• a plurality of electrically-conductive rods protruding from the second electrically conductive surface and being located around the plurality of ridges, each having a leading end opposing the first electrically conductive surface, wherein,
• the plurality of ridges include
• a first main ridge,
• a second main ridge,
• a third main ridge,
• a fourth main ridge,
• a first connection ridge connecting one end of the first main ridge and one end of the third main ridge,
• a second connection ridge connecting one end of the second main ridge and one end of the fourth main ridge,
• a first bypass ridge connecting the one end of the first main ridge and the one end of the second main ridge, and
• a second bypass ridge connecting the one end of the third main ridge and the one end of the fourth main ridge;
• a first waffle-iron ridge waveguide is created between the waveguide faces of the first main ridge, the first connection ridge, and the third main ridge and the first electrically conductive surface;
• a second waffle-iron ridge waveguide is created between the waveguide faces of the second main ridge, the second connection ridge, and the fourth main ridge and the first electrically conductive surface;
• a first bypass waveguide is created between the waveguide face of the first bypass ridge and the first electrically conductive surface;
• a second bypass waveguide is created between the waveguide face of the second bypass ridge and the first electrically conductive surface;
• a portion of an electromagnetic wave which propagates in the first waffle-iron ridge waveguide from another end of the first main ridge toward another end of the third main ridge is propagated, via the first bypass waveguide, in the second waffle-iron ridge waveguide toward another end of the fourth main ridge;
• a portion of an electromagnetic wave which propagates in the first waffle-iron ridge waveguide from the other end of the third main ridge toward the other end of the first main ridge is propagated, via the second bypass waveguide, in the second waffle-iron ridge waveguide toward another end of the second main ridge;
• spacings da1, da2, da3 and da4 respectively exist between the first electrically conductive surface and the waveguide faces of the first, second, third, and fourth main ridges;
• spacings db1 and db2 respectively exist between the first electrically conductive surface and the waveguide faces of the first and second connection ridges;
• spacings dc1 and dc2 respectively exist between the first electrically conductive surface and the waveguide faces of the first and second bypass ridges;
• and
• the relationship db1, db2<da1, da2, da3, da4, dc1, dc2 is satisfied.