Anything that conducts electricity is an antenna, (usually a wire, but it could be your body) but the basic unit from which we build antennas is a wire, 1/2 wave length long having a connection in the middle to equipment. Called a dipole, it is an efficient radiator of alternating current electrical energy and is a standard of reference for other antennas.
All radio antennas are comprised of parts and pieces of dipoles. In order to garther more energy, the parts, made from wires or reflecting surfaces, must funnel or direct the energy in phase into a transmission line , the line that connects an antenna to equipment. The line is usually co-axial, meaning one inside wire covered with insulating material, that covered in turn with copper braid, or aluminum.
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