Doublets, dipoles, and other Hertzian antennas

A doublet antenna is a form of a dipole that is balanced with respect to ground. These antennas are fed in the center, which point will be either a current node or voltage node depending on the design of the particular antenna. A half-wavelength dipole is the first antenna that a new ham operator or short-wave listener may put up. These antennas are low cost, easy to build, and have a delightful tendency to work well with only a little muss and fuss. They are thus well suited to the newcomer. The BALUN transformer is used to convert between balanced and unbalanced loads. In the context of the dipole, the feedpoint is balanced with respect to the ground, while the transmitter output is unbalanced with respect to the ground. The half-wavelength dipole is a resonant antenna, and it works best only on and near the center design frequency. The folded dipole antenna has a wider bandwidth than the common dipole, although at the expense of a little constructional complexity. This antenna consists of a loop of wire made from a half-wavelength section of twin-lead or parallel transmission line. Multiband tuned doublet antenna is a strong contender today for those who want a multiband antenna, provided that the bands are harmonically related. It consists of a nominal half wavelength wire radiator. The antenna may perform well on harmonics of this frequency, and perform at least somewhat on other frequencies as well.