  We report spin-wave excitations in annular antidot lattice fabricated from 15
nm-thin Ni80Fe20 flm. The nanodots of 170 nm diameters are embedded in the 350
nm (diameter) antidot lattice to form the annular antidot lattice, which is
arranged in a square lattice with edge-to-edge separation of 120 nm. A strong
anisotropy in the spin-wave modes are observed with the change in orientation
angle ({\phi}) of the in-plane bias magnetic field by using Time-resolved
Magneto-optic Kerr microscope. A fattened fourfold rotational symmetry, mode
hopping and mode conversion leading to mode quenching for three prominent
spin-wave modes are observed in this lattice with the variation of the bias
field orientation. Micromagnetic simulations enable us to successfully
reproduce the measured evolution of frequencies with the orientation of bias
magnetic field, as well as to identify the spatial profles of the modes. The
magnetostatic field analysis, suggest the existence of magnetostatic coupling
between the dot and antidot in annular antidot sample. Further local
excitations of some selective spin-wave modes using numerical simulations
showed the anisotropic spin-wave propagation through the lattice.
