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

Thanks Jim N6PJQ

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

In article , Richard Clark
wrote:

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.

snip

Hello, and the only fan antenna that I have any experience with is the
venerable 2-6 MHz twin fan transmitting antenna used on USN combat ships.
This antenna consists of two sets (port, starbaord) of three sloping wires
strung from a yardarm on the stack to the feedpoint on the deck. A VSWR
of 3 or less is typically achieved using a fixed passive LC network. By
design, most of the radiation actually comes from RF currents induced on
the stack by the fan wires. Sincerely,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

Thanks for your input.

Jim N6PJQ

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

Thanks Jim N6PJQ

"J. B. Wood" wrote in message
...
In article , Richard Clark
wrote:

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.

snip

Hello, and the only fan antenna that I have any experience with is the
venerable 2-6 MHz twin fan transmitting antenna used on USN combat ships.
This antenna consists of two sets (port, starbaord) of three sloping wires
strung from a yardarm on the stack to the feedpoint on the deck. A VSWR
of 3 or less is typically achieved using a fixed passive LC network. By
design, most of the radiation actually comes from RF currents induced on
the stack by the fan wires. Sincerely,

John Wood

Supplementing, if I may, many fan-wire antennas are fed from the mast. (I've
climbed most of the ships in the Pacific Fleet at one time or another.)
Coax into the matching network box and port/starboard feedwires out.

The traditional design used the fan from 2-6, another antenna, maybe a cage
for 4-12 and a third, maybe a discone or trussed whip, from 10-30. These
are fed by four- or eight-channel multicouplers in Radio.

A newer design, called HFRG, for HF Radio Group, uses a 2-9 fan and maybe
twin whips from 8- 30. HFRG tolerates a 4:1 SWR ... I don't think you can
get a match of 3:1 over a wide range like 2-9 or 8-30. (In a lab, maybe.)
I Googled for AN/URC-131 and got:
http://www.rfcomm.harris.com/product...s/anurc-131v.p
df It's mostly a Harris puff piece, but there's a little techie stuff.

I have to say "maybe" a lot because of differences between classes and even
between different levels of modernization within a single ship class.

John
KD6VKW
US Navy since Jan, 1962, in many capacities.