feed position of bow tie antenna

The simple answer is "in the middle", but I think you want to know something that is not that simple.

Yes..i don think always at the centre it will be 50 ohms..so,how will you match the feed with the antenna if u r using coaxial feed

Is your bow antenna above a ground plane, as this has large influence on input impedance?

feeding a dipole off-center, will raise the impedance, but you get a large common mode component, that will increase the common mode current in the coaxial feed line. The common mode current contributes to the radiation pattern (mostly not desired).

If you need some form of matching, you may use a shunt component (L or C) and change the length of the elements to get the requried impedance. This method works when the input impedance is below what you want.

I’m planning to make a microstrip bowtie antenna:either slot or printed Can you tell me which is the dimension which mostly affects the highr cutoff frequency and bandwidth for bowtie antenna..can you please explain me with some mathematical relation