Antenna unit with a top cover painted in one of various colors

1. An antenna unit comprising:

a bottom plate having a main surface;

an antenna mounted on the main surface of said bottom plate;

an intermediate cover attached on the main surface of said bottom plate so as to cover said antenna; and

a top cover fitted to said intermediate cover so as to cover said intermediate cover;

wherein said top cover comprises a plurality of fixing pieces extending towards said bottom plate on an inner surface thereof, each of said fixing pieces having a stopper claw at a tip thereof;

wherein said intermediate cover comprises a plurality of engaging parts for receiving the stopper claws, the engaging parts being provided at positions corresponding to the stopper claws, respectively; and

wherein said top cover is fitted to said intermediate cover by engaging said stopper claws with said engaging parts.

2. The antenna unit as claimed in claim 1 , wherein said antenna unit has a symmetrical structure which is symmetric with respect to a symmetric plane, and wherein said fixing pieces are substantially symmetrically positioned on the inner surface of said top cover with respect to the symmetric plane.

3. The antenna unit as claimed in claim 2 , wherein said fixing pieces are positioned on the inner surface of said top cover at regular intervals.

4. The antenna unit as claimed in claim 3 , wherein said top cover comprises at least six of said fixing pieces, and said intermediate cover comprises at least six of said engaging parts.

5. The antenna unit as claimed in claim 1 , further comprising an elastic sheet mounted around the main surface of said bottom plate, said elastic sheet being sandwiched between said intermediate cover and said bottom plate.

6. The antenna unit as claimed in claim 1 , further comprising a gasket, made of an elastic member, for covering at least an outer edge of said bottom plate, said top cover having a rim edge which comes into contact with a rim edge of said gasket when said top cover is fitted with said intermediate cover.

7. The antenna unit as claimed in claim 1 , further comprising:

an elastic sheet mounted around the main surface of said bottom plate, said elastic sheet being sandwiched between said intermediate cover and said bottom plate; and

a gasket made, of an elastic member, for covering at least an outer edge of said bottom plate, said top cover having a rim edge which comes into contact with a rim edge of said gasket when said top cover is fitted with said intermediate cover.

8. The antenna unit as claimed in claim 1 , wherein said top cover is painted.

9. The antenna unit as claimed in claim 8 , wherein said top cover is painted in one color selected from a plurality of colors.