You need to change the length of the transmission lines between each antenna so all the antennas are in phase, or 360 degrees out of phase, or 720 degrees etc. It is usual to do this by putting 'U' bends in the lines.

Dear Naveen Muthukumar ,

I would have to see the distribution network, but I understand that it is a series-fed array. Maybe in planar technology? To have a broadside pattern, effectively you need all elements to be fed with the same phase. If you are using CST or HFSS it is easy to see what phase you have in each element. Check this and try to make the adjustments that Malcolm discusses above. I hope you can sort it out,

Miguel

Hello,

As we know a linear or planar array antenna whose direction of maximum radiation is perpendicular to the line or plane of the array is known as broadside array, whereas if the direction of maximum radiation lies along the line or the plane of the antenna array, then it refers to an end-fire array. So, You need to fed all the array with same phase of feeding for broadside. Few research papers are attached.

Thanks,