Folded dipole step up ratio calculator


This calculator finds the step up ratio of a simple two conductor folded dipole with main elements of diameter d and D, and S centre to centre spacing. Element d is the one with the feed point terminals.

d (mm):
D (mm):
S (mm):
α (Balanis' current ratio):
Z step up ratio ((α+1)2):
Z0 (Ω):

The calculator does not do a lot of error checking, if you enter nonsense, it will produce nonsense. It uses a formula that ignores the effect of each conductor on the flux distribution due to current in the other conductor, so it is an approximation (which falls down as the conductors are made relatively close). It also assumes that both conductors are immersed in an identical electric field gradient, and assumption that fails where S is large electrically. Dielectric is assumed to be a vacuum (air is well approximated).

The dimension units are shown in mm, but they can be any consistent units.

α is the ratio of current in the main conductor to the current in the gamma arm, both at the feed end of the gamma arm. α+1 is the ratio of the current in the centre of a plain dipole to the current into the gamma arm (for the same radiated power).

The same step up ratio applies to a T match and Gamma match. Z0 is the characteristic impedance of the air spaced conductors, useful for design of Gamma and T matches, or to calculate the stubs shunting a folded dipole feed point.




Version Date Description
1.01 09/10/2013 Initial.

© Copyright: Owen Duffy 1995, 2021. All rights reserved. Disclaimer.