problem creating halfwave simple slot antenna radiation pattern

[yefj]

Hello, I am trying to build a half wavelength slot antenna at 10Ghz,so lambda=300/10=30 lambda/2=15 as shown bellow.
for some reason i got two halfs of wavelength in the current distribution.
my slot length is 15mm and i am at 10Ghz.the slot is being excited by descret port.
Why i get two half wavelength?
Where did i go wrong?

 

[PlanarMetamaterials]

There doesn't appear to be anything wrong, the field variation appears to be a half wavelength (plus a bit on the left, perhaps?)

I assume there is no dielectric substrate used?