A dielectric substrate for transmitting a signal with a frequency f0 includes a dielectric and a copper film pattern arranged on a first surface of the dielectric. The copper film pattern has a first dimension L in a direction parallel to a propagation direction of an electromagnetic wave that has the frequency f0 and that propagates on the first surface, and the first dimension L is given by: L = 1 ɛ r - 1 ⁢ k ⁢ ⁢ λ 0 where εr represents a relative permittivity of the dielectric, k represents a constant in a range of 0.15 to 0.70, and λ0 represents a free space wavelength of the signal.