Re: NEC-LIST: What is Babinet Principle?

Samson Malaka wrote:
>
> What is really the Babinet Principle?

Consider a pair of complementary antennas, say a planar dipole and a
slot of identical size in a metal sheet.

Babinet's principle states that the product of the impedances of
complementary antennas is given by

                       Z1 * Z2 = n^2/4 ,

where Z1 is the impedance of the first antenna, Z2 is the impedance of
the second, and n is the intrinsic impedance of free space.

Babinet's principle is useful because it allows one to predict the
impedance of an antenna which may be difficult to analyze (e.g., a
slot) from knowledge of the impedance of an antenna which may be
easier to analyze (e.g., a planar dipole).

If the antenna and its complement are the same (some frequency-
independent spiral antennas fall into this category), then they are
referred to as self-complementary. In that case,

                  Z1 = Z2 = n/2 = 188.5 ohms.

--
Dave Michelson
dmichelson_at_home.com