I dont know whether you are still interested in knowing the history of how vivaldi antennas have been given this name. But i am sharing this information here.
Vivaldi antenna design structure was originally and first presented by p.j.Gibson in 1979 in IEEE European Microwave Conference paper entitled as 'The vivaldi aerial'. He presented for the first time a vivaldi antenna having an impedance bandwidth from below 2GHz to above 40GHz with 10dBi gain and -20dB side lobe levels.
Antonio Vivaldi was a composer from the Baroque period. Why is his name associated with the tapered slot antenna? The answer can be found in ADVANCED RADIO ASTRONOMY ACROSS EUROPE, edited by Alastair G. Gunn, a Springer publication. According to an article on the PHAROS JRA focal plane array, it "received its name from a resemblance to the shape of a cello or violin, instruments used by Antonio Vivaldi, the designer's favourite composer".
By the way, you won't see the connection to this antenna and a cello unless you examine an array of Vivaldi antennas...
I hope it is clear to you that how it got this name of vivaldi antenna !!!