An apparatus and method for electromagnetic heating of a hydrocarbon formation is presented. The apparatus is a radio frequency antenna module in a radio frequency antenna for delivering electromagnetic energy generated by a generator into the hydrocarbon formation. The antenna module comprises: a conductive member; at least one conductive sheath with a first and second end surrounding at least one portion of the conductive member; at least one electrical coupler electrically coupled to the conductive member and the at least one conductive sheath for receiving the electrical energy; and an electrically insulating seal inserted at the first and second end of each of the at least one conductive sheath between the conductive member and the conductive sheath to maintain an enclosed cavity defined by the conductive member, the conductive sheath and the electrically insulating seal.