the problem from 2D pattern in slot antenna by HFSS

hi ,I did a simple slot antenna in HFSS using HFSS design kit to build the model.
the target freq is 0.95GHz

the S11 and smith chart is good

so I simulatate the 2D pattern for slot antenna for single freq point at 0.95GHz
but I found something wrong in my 2D pattern

accroding to the theory in textbook, the Omni-direction pattern should appear at XZ plane, null at YZ plane in my simulation.
but my simulation result show that Omni-direction pattern should appear at YZ plane, null at XZ plane in my simulation.
It is totally different from the theory. what happen to my simulation? thank you
my simulation:slot.rar

P.S I found a paper which had same situation like me, but i can't clearly understand what it write
05697298.pdf