English: Diagram of a J-pole antenna, a vertical end-fed half-wave omnidirectional transmitting antenna used in the shortwave frequency bands. It consists of a vertical element a half wavelength (${\displaystyle \lambda /2}$) long, fed in series with a quarter wavelength (${\displaystyle \lambda /4}$) transmission line stub, with the coaxial cable feedline (F) from the transmitter attached along the stub. The stub serves as an impedance matching device to transform the high feedpoint impedance of the half-wave antenna down to match the impedance of the coaxial cable.