NEC-LIST:Lindenblads, etc.

I am looking for some information (i.e. practical modeling hints) on
modeling a few omnidirectional (in horizontal plane) circularly polarized
antennas. Two alternatives that have come up (because we can read Kraus
(page 732-733) as well as anyone) are the Lindenblad (4 tilted dipoles in a
circle) and the slotted fat dipole with two drive points.

For the Lindenblad, a popular implementation uses the supports for the
dipole as a parallel feed line/matching transformer to get 50 ohms at the
feed point. Typically, the elements (and the feed line) would be 1 cm in
diameter, with a bend radius of a cm or so(see, for instance, the antennas
used by the FAA at airport control towers for VHF). How best does one
model the bend in the rod? Do you just build two fat wires and hope for the
best (we're not looking for 0.0001% accuracy here...), or is it better to
model it as a bunch of thin wires at the "surface" of the conductor.

Likewise, for the slotted fat dipole, assuming you model it as a circular
array of wires, how many wires of what diameter? Any tricks on the
circumferential connection (clearly, you need to connect the wires at the
ends of the slots, and at the ends of the elements, but what about other
places?

Thanks...

Jim Lux
Spacecraft Telecommunications Equipment Section
Jet Propulsion Laboratory
4800 Oak Grove Road, Mail Stop 161-213
Pasadena CA 91109

818/354-2075, fax 818/393-6875

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