How to design an antenna on NEC-Win plus+ with given specs

Aoa, hellow to everyone....i have been given a project from wave propagation lab to design an antenna on software with following specifications... please help....

we are bound to use NEC - Win software.

Antenna Specifications:

Gain >13db

Beam Width <50 degree

Solution Frequency Depend on your Design

Ratio b/w major and side lobe >15 dB

Front to Back Ratio >10db

Note: can use any type of antenna

A similar project with the following specifications:
Name of antenna ?
Gain >30dB
BW <50 degree
Solution Frequency Depend on your Design
Ratio b/w major and side lobe >25 dB
Front to Back Ratio > 25 dB