  We theoretically study plasmonic antennas featuring areas of extremely
concentrated electric or magnetic field, known as hot spots. We combine two
types of electric-magnetic complementarity to increase the degree of freedom
for the design of the antennas: bow-tie and diabolo duality and Babinet's
principle. We evaluate the figures of merit for different plasmon-enhanced
optical spectroscopy methods: field enhancement, decay rate enhancement, and
quality factor of the plasmon resonances. The role of Babinet's principle in
interchanging electric and magnetic field hot spots and its consequences for
practical antenna design are discussed. In particular, diabolo antennas exhibit
slightly better performance than bow-ties in terms of larger field enhancement
and larger Q factor. For specific resonance frequency, diabolo antennas are
considerably smaller than bow-ties which makes them favourable for the
integration into more complex devices but also makes their fabrication more
demanding in terms of spatial resolution. Finally, we propose Babinet-type
dimer antenna featuring electromagnetic hot spot with both the electric and
magnetic field components treated on equal footing.
