Dipoles
Tuned half-wave dipoles have been among the most important antennas from the
beginning of rf-technique. The characteristics of half-wave dipoles have
been calculable very early using the Maxwell and Hertz equations. Therefore the half
wave dipole became a reference antenna. The ideal (lossless) half-wave dipole has an
isotropic gain of 2.15 dBi and an impedance of 73 Ohm. The directional pattern is circular in
the H-plane, "8-shaped" in the E-plane with the maxima perpendicular on the dipole axis.
The half-power beamwidth (-3 dB) is approx. 78°. The impedance of real dipoles is
depending on the thickness/length ratio of its elements, typical values are 60-70 Ohm.
Dipoles for industrial applications are available in the frequency range from 30
MHz to up to approx. 4 GHz. The dipole elements are length variable (telescopic) or
with fixed length, the latter especially above 1 GHz. The most important applications are
test site evaluations (NSA, normalized site attenuation) and the determination of ERP
(Effective Radiated Power) respectively EIRP (Effective Isotropic Radiated Power).
