It's difficult to say for yogi-uda nano antenna (since I don't know much about yogi-uda antenna)but the fundamental idea is plasmon red shifts and broadens with increasing size due primarily to retardation effects. Plasmon resonance frequency changes with particle dimension because the electron oscillation has to accommodate the difference in electromagnetic phase between one end of the particle and the other (i.e., radiative depolarization effects).opposite charges are separated by roughly one particle diameter in a dipole mode, so that the interaction of one end of the particle to changes produced in the other end takes place with a phase delay of the order of 4*pi*R/(Lambda)m, and consequently, the period of one mode oscillation increases to accommodate this delay. Quadrupoles and higher-order modes produce more nodes in the distribu- tion of the polarization charges induced on the surface of the particle (the number of nodes is proportional to l), which reduce the effective interaction distance, so that the shift of an l mode in a particle of radius R is comparable to the dipole shift for radius R/l