Antenna design engineering consists ofTransmission line a hybridHybrid design of transmission lineTransmission line and the pure radiator. Transmission linesTransmission line are essential to interface the portPort to the radiator. Hence, comprehension of transmission linesTransmission line from a full-waveFull-wave solver perspective is essential. A wide variety of commonly used transmission linesTransmission line are discussed in this chapter. The chapter begins with a discussion of coaxialCoaxial line. The nuances of the energy transmission within the coaxialCoaxial line are also included. The popular microstripMicrostrip lines are also explained in this chapter with special emphasis on the consequences with different types of portsPort. Coplanar wave guide (CPW) line is also comprehensively explained in this chapter. Definitions and software characteristics of substrateSubstrate integrated waveguideWaveguide (SIW) and strip-line-based designs are also investigated in this chapter. A detailed account of characteristics of waveguidesWaveguide is included at the end of this chapter.