GuM is absolutely correct. The dimensions you used are too small for the current UHF band.
The Grey-Hoverman he directed you to is an excellent, well designed & modeled antenna.
If you are set on building a bow-tie antenna, look at the ones from McClapp.
http://m4antenna.eastmasonvilleweather.com/
They were tested & modeled also by holl_ands, a very well respected & knowledgeable member of the OTA antenna community
http://imageevent.com/holl_ands