2 element dipole, so-called Driven Element or DE for short, A Balun Transformer provides balanced-to-unbalanced connection and impedance conversion. Electrical energy may flow into the Dipole radiating from it as Electromagnetic (EM) Radiation or, EM striking the Dipole is transformed into Electricity flowing through its conductors, hopefully most of which is transmitted away through the Balun. The dipole is usually tuned to the frequency of interest geometrically by making it a half wavelength in size. It comes in several variations, 2 of which are most used, the dual element and the loop seen below.

http://en.wikipedia.org/wiki/Balun

Half wavelength

A quirk of Nature allows balanced Radio Frequency (RF) electrical energy to be coupled to an unbalanced shielded wire (Coaxial Cable) by a trick in geometry. Seen below, 2 lengths of Coax are connected to a third in a convenient manner to achieve the desired effect, balanced energy on the right and unbalanced energy on the left. This arrangement is shown connected to the 2 Dipoles in the illustration to the left represented as small red boxes.

A different arrangement or alternative to the simple Dipole is seen below as two 90 degree quarter-wave elements. This accommodates both vertically and horizontally polarized RF energy to be converted at the same time with one set of DEs. On the right is another alternative. By angling the horizontal Elements at 45 degrees, the Dipole now is vertically directional instead of horizontally directional as the Dipole on the left. Note that directionality is not polarization, these dimensions are separate.

Through proper spacing, addition, and modification of Balanced Baluns, a horizontal antennae array may be fashioned that lays close to the ground and focuses it reception or transmission direction vertically with a fan pattern perpendicular to the array of elements. Additional directivity and efficiency is provided by the addition of a reflecting screen placed parallel to the Earth’s surface below the array near the quarter wave position. Multiplying this simple 8 Element Array several hundred times creates the existing Antennae Arrays used by the NAVSPSUR System.

Details of NAVSPSUR Antennae Arrays

by: Jay Salsburg

Balun for next Array