Referring to FIGS. 1 and 4 together, the second reference-phase coupling electrode 423 and the second antiphase coupling electrode 425 may be disposed in another diagonal direction, e.g., ?45 polarization direction, connecting third point P3 and fourth point P4 of the radiation plate 50. One end 427 of the second reference-phase coupling electrode 423 may be disposed adjacent to third point P3 of the radiation plate 50, and the second reference-phase coupling electrode 423 may extend from a location adjacent third point P3 of the radiation plate 50 toward fourth point P4 of the radiation plate 50. In addition, one end 428 of the second antiphase coupling electrode 425 may be disposed adjacent to fourth point P4 of the radiation plate 50, and the second antiphase coupling electrode 425 may extend from a location adjacent fourth point P4 of the radiation plate 50 in parallel with the radiation plate 50 toward third point P3 of the radiation plate 50.

Therefore, the second feed line 420 of the second feeding board 40 may supply a reference-phase signal to third point P3 of the radiation plate 50 and an antiphase signal to fourth point P4 of the radiation plate 50. In addition, the reference-phase signal may be fed from third point P3 toward fourth point P4 of the radiation plate 50, and the antiphase signal may be fed from fourth point P4 toward third point P3 of the radiation plate 50.