Small UWB Square Monopole Simulation Problem

I am trying to reproduce the result of the attached paper. It's a simple square monopole planar antenna. But somehow can't produce the result.
I am using 50 ohm waveport (10*w, 8*h). lamda/4 distance radiation box and substrate. delta s = 0.02. discrete sweep.

I have attached my Hfss file and pdf of research paper. plus results.

Waiting for replies
Regards

2009-Small Square Monopole Antenna With Inverted T-Shaped Notch in the Ground Plane for UWB Appl.pdf2009tshaped_waveguide.rar

talha.arshed,

1. give 3.5*w and 4*h as the dimensions for the 50ohm port.

2. try giving a radiation box and check for the results.