[Antennas] Inverted Vee/Turnstyle

[Terry Conboy]

At 06:45 PM 2007-09-29, Joe wrote:
>Can anyone with some modeling software please model this for me?
>Picture a standard turnstyle,  ya know  the crossed dipoles phased 
>90 deg and all  that,,
>But  droop  the dipoles into inverted vees.
>
>Now i assume   above and below it's still  circularly 
>polarized,  but of course  what is the patterns 
>now  since  say  below  it is like a vee beam?  and above?  who knows.
>
>Now  the real  question is  from the sides,,
>what polarity dominates?
>since  you'll  be broadside to one of the dipoles like a inverted 
>vee and i assume again assuming  horizontally polarized,
>but you also  have the equvialent of a 1/4 wave sloper facing you 
>vertically polarized,

I modeled two crossed inverted vees in free space using EZNEC+ 5.0.10 
with 45 degree droop, fed with equal 90 degree phase difference 
currents.  Feedpoint impedance of each element is about 43 ohms at 
resonance (#12 bare copper wire at 7.15 MHz).  The two elements were 
offset vertically by 6 inches (0.004 wl) to prevent contact.

The signal at the zenith is all right-hand circular with 1.3 dBic 
gain (RH vs LH depends on the sense of the 90 degree 
phasing).  Toward the ground it is all left-hand circular with 1.3 
dBic gain.  On the horizon, both circular polarization signals are 
very nearly equal with -3.8 dBic and omni within about +/- 0.5 dB.

Looked at with linear polarization, the horizontally polarized 
azimuth pattern is essentially omni with -1.4 dBi gain and the 
vertically polarized azimuth pattern is also omni, but the signal is 
about 8.5 dB down.

A single inverted vee is horizontally polarized broadside with 1.1 
dBi gain, but has some vertically polarized signals off the ends with 
-6.8 dBi gain.  The half-sloper analogy is probably misleading, since 
the mirror half of the antenna makes it a very different system.

BTW, vee beams require more than 1/4 wavelength legs to develop any 
gain over a dipole, and even so, they are bidirectional (unless end 
terminations are used).  [I've seen some antennas on the Internet 
that claim unidirectional gain with a horizontal "vee beam" with 1/4 
wl legs, but this is definitely wishful thinking!]

Note that all the numbers above for gain and impedance will be 
significantly modified when operated at modest heights over real earth.

73, Terry N6RY