I have one question about dipole connected to grounded receiver.

I've made dipole antenna. One "pole" is connected to center line of coax,
the other to shield line of the coax. Cable goes down to receiver and
connects with BNC. The BNC is (of course) connected to case. The case is
grounded.

Can someone tell me, what is te purpose of the dipole if one of the poles is
grounded? I mean, why i built two poles when one goes directly to
ground!Shouldn't it be easier to build just a monopole? I'm puzzled....

Thanks in advance
tom