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Managing antennas with telescopic elements (tapering)

Altair Forum User

Hi everybody,

thank you for accepting me in the forum, this is my 1st post but i hope will follow others for helping someone and for asking your help.

As mentioned in the title, I'm making some exercises for understanding better FEKO but looking around examples and forum posts I didn't find answer to the following problem: how I do represent in FEKO an antenna made of rigid aluminum telescopic elements (tubes)?
By using connected wires with different radius? By using connected cylinders, also woth different radius? Or there is a different way?
Telescopic elements have difference resonance frequency and impedance compared to singolar radius ones, so the different configurations should be took in count.

What do you suggest? Is the mesh managed better in one or both cases?

Thanks in advance for you kind reply,

Kevin

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JIF

Hello kevinwhite,

What you use really depends on the frequency and radius in question. You can model this structure with cones that will be meshed into triangles if the radii of the elements are large (sizable fraction of a wavelength). If you are working at low frequencies and the radii are small (much smaller than a wavelength), you can use segments. EDITFEKO has a card (BL card with tapered radius) to create wires where the segments vary in diameter along the wire. The same feature does not yet exist in CADFEKO though.

Altair Forum User

Thanks Jif for your kind reply.

For 130-150 MHz and up tapering is not a problem becouse elements can be designed with a single tube (and constant radius).

On lower frequencies telescopic elements are necessary. For example at 30 MHz the shift between telescopic and no telescopic element in a yagi antenna is up to 700 kHz.

The BL card you suggest seems to approximate a telescopic element to a regular truncated cone geometry. So I presume this should approximate enough the real element and manage better the element meshing.