A wellbore apparatus may include first and second tubular members joined together in end-to-end relation, the first tubular member having a reduced outer diameter end portion. The wellbore apparatus may further include a removable modular antenna assembly comprising a cylindrical dielectric housing removably positioned on the reduced outer diameter end portion of the first tubular member, at least one antenna coil carried by the cylindrical dielectric housing, and a first electrical connector coupled to the at least one antenna coil. The wellbore apparatus may also include resistivity processing circuitry coupled to the first electrical connector to determine an electrical resistivity of a wellbore based upon the at least one antenna coil.