help in designing vivaldi antenna

Hi,
I need to design vivaldi antenna for WLAN application.
i need to know how to determine its width and length of the antenna, can anyone help me? i really dont have any idea on how to design the antenna.
Is there any specific formulas or design procedures to determine the parameters?
i know that the curve of the slot use exponential functions but how about the length and the width?

Thank You.

Hi
Refer
McGraw-Hill - Antenna Engineering Handbook
pcup

hi pcup, thanks for your advice, if its not troubling you, do you by any chance know good IEEE article I colud refer to? I have read lots of the related article but I still don't know how to determine the lenght and its width, I have gone through several designs, but with no avail. Thanks in advance for your help.

Hi,
It depends on Field of Application like Medical Imaging, Snow Radar...
Which specific field you want to design antenna it depends.
If i am not wrong
Pcup