On Wed, 08 Mar 2006 19:14:02 GMT, "NA"
wrote:

Can anyone tell me about "fan antennas" like those used on the large navy
ships.

Hi Jim,

It is an array of co-planar, parallel monopoles driven at the same,
common point. The size of each in the array is different spanning
from short to long such that at least one is resonant within a wide
band of frequencies.

Two of these hung in the air in dipole fashion become the skeletal
version of the Bowtie antenna.

When the fan of wires are formed into an equal sized array in a circle
(with their far ends attached in a loop); you have a conical antenna
(cone shaped, driven at the pointy end against ground).

All such designs have a reputation for being widebanded, but basically
only as useful as a quarterwave monopole (at any of the resonant
frequencies). For the conical versions, they can resonate over a
considerably wide band, and in fact up to 6 to 10X of the first
resonance. Unfortunately, having a resonance this high does not mean
it is useful. This is because the antenna will be so very long at
that extreme harmonic that most of its radiation will be directed
along its length rather than broadside. This may be an unintended
consequence. The fan design, on the other hand, will have a short
length element that will provide the expected pattern.

73's
Richard Clark, KB7QHC