antenna sidelobes

Hi, all. I'vw already posted some messages on similar topics, but this will be summing up.

i have to design and analize properties of a leaky-waves antenna. The structure is a rectangular waveguide with a long slit along it's narrow side. I use CST Microwave Studio to simulate this structure.
Here's the example of structure:

here"s the example of radiation:

Of cource there"s a problem with sidelobes level. And I thought this problem is solved in this article:
http://ieeexplore.ieee.org/xpl/freea...number=4051241
Traveling-Wave Slot Antennas
Hines, J.N. Rumsey, V.H. Walter, C.H.
The Antenna Laboratory, Department of Electrical Engineering, The Ohio State University Research Foundation, Columbus, Ohio;

This paper appears in: Proceedings of the IRE
Publication Date: Nov. 1953
Volume: 41, Issue: 11
On page(s): 1624-1631
ISSN: 0096-8390
Digital Object Identifier: 10.1109/JRPROC.1953.274190
Current Version Published: 2007-01-08

In this paper it's recommended to control leakeage along the slit by changing the slit geometry (to obtain gaussian amplitude distribution) instead of a straight slit- here's the example from paper:

So, i simulated this structures in CST but got no good result.

Simulation with straight slit:

Simulation with gaussian slit:

So, the question is - this is a simulation problem, or some other kind of problem?

attached Rumsey & Walter paper

I am not an expert on these things, but that is a very long slot! I would think that a series of short slots would work better. For a leaky waveguide, you want to LIGHTLY couple into each aperture.

There must be a pretty big vswr in the waveguide where that slot starts!

well, is there any change after your modification

i'm facing some problem in designing rectangular waveguide.could you please help me