| 摘要 |
PROBLEM TO BE SOLVED: To provide an inexpensive antenna device that is able to stably measure a melting pig iron level, etc., inside a converter over a long time by surely preventing dust accumulation that inhibits transmission and reception of a microwave. SOLUTION: If a plurality of holes 14a which are 1/4 to 1/7 of the wavelength of a microwave in dimensions and the total opening area of which also occupies 0.5 to 0.8 of the total area of a subreflector 14 are opened in the subreflector 14 for reflecting the microwave radiated from a primary radiator 12a in the concave surface direction of a main reflector 13, the subreflector 14 can reflect the microwave radiated from the primary radiator 12a almost completely, and dust is also prevented from accumulating on the upper surface of the subreflector 14.
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