Analysing a Coaxial skirted colinear array.

I wish to analyse a multi band colinear array at VHF.

This antenna consists of a central vertical tube of about 0.75 inch diameter,
 which supports a number of quarter wavelength coaxial tubes which are
connected to the central tube at one end only, to form both dipoles and
insulating chokes.

e.g. Drawn horizontally:-

      -------i V-------i -------i V-------i -------i V-------i --------i
-------------I---------I---------I---------I---------I---------I---------I--
-------------I---------I---------I---------I---------I---------I---------I---
      -------i -------i -------i -------i -------i -------i -------I

where the drive points are shown as V. (Sorry about the ASCII graphics)

The antenna is rotationally symmetric, except for the sources.

I propose to create one set of vertical wires describing the tube and skirt
surfaces, and then GR it 6 or 8 times. I would create a N.G.F file from
this, and than add the source wires in the NX next run.

Questions:

1. Is it ok to put parallel segments closer than the segemnt length apart ?

2. If I use one segment for the shorting disk, do I have to use the same
short segment length on the vertical parts ?

3. Can anyone suggest a way of reducing the number of segments in the
analysis ?
   I wish to experiment with two frequency antennas.

73,
ZL2BDV.
sringe@actrix.gen.nz = Steve Inge, ZL2BDV. Engineering Analyst,
Broadcast Communications Ltd, PO Box 98, Wellington, New Zealand.
Home=9 High St, Island Bay, Wellington, New Zealand.
Received on Mon May 27 22:08 MET 1996