Editing Electrical length (section)

=== Electrically short antennas ===
An electrically short conductor, much shorter than one wavelength, makes an inefficient radiator of [[electromagnetic wave]]s.  As the length of an antenna is made shorter than its fundamental resonant length (a half-wavelength for a dipole antenna and a quarter-wavelength for a monopole), the [[radiation resistance]] the antenna presents to the feedline decreases with the square of the electrical length, that is the ratio of physical length to wavelength, <math>(l/\lambda)^2</math>.    As a result, other resistances in the antenna, the ohmic resistance of metal antenna elements, the ground system if present, and the loading coil, dissipate an increasing fraction of transmitter power as heat.  A monopole antenna with an electrical length below  .05<math>\lambda</math> or 18° has a radiation resistance of less than one ohm, making it very hard to drive.

A second disadvantage is that since the capacitive reactance of the antenna and inductive reactance of the required loading coil do not decrease,  the [[Q factor]] of the antenna increases; it acts electrically like a high Q [[tuned circuit]].  As a result, the [[bandwidth (signal processing)|bandwidth]] of the antenna decreases with the square of electrical length, reducing the [[data rate]] that can be transmitted.  At [[very low frequency|VLF]] frequencies even the huge toploaded wire antennas that must be used have  bandwidths of only ~10 hertz, limiting the [[data rate]] that can be transmitted.