Multi-band antenna and method for designing multi-band antenna

A multi-band antenna is capable of transmitting/receiving electromagnetic waves at least in a first wavelength band of a first center wavelength λ1 and a second wavelength band of a second center wavelength λ2, which is shorter than the first center wavelength λ1, the multi-band antenna including at least one antenna unit, wherein the at least one antenna unit includes: a first radiation conductor; and a first ground conductor spaced apart from the first radiation conductor with a dielectric having a relative dielectric constant εr interposed therebetween, wherein: the first radiation conductor and the first ground conductor each have a planar shape having a pair of opposing first sides; and a distance Lrf1 between the pair of opposing first sides of the first radiation conductor and a distance Lg1 between the pair of opposing sides of the first ground conductor satisfy expressions below:0.2λ1/εr1/2≤Lrf1≤0.7λ1/εr1/2; and0.7λ2/εr1/2≤Lg1≤1.75λ2/εr1/2.