Greetings to all the antenna experts here!

I want to create horizontally polarized antenna, low profile, located above
large ground plane. And I need it to be omnidirectional (sort of) and have
sufficient gain in horizontal plane.

My frequency of interest is 900 MHz. The ground plane is a roof of a car.

I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount it
above the ground plane.

Any ideas?

Thank you,

Andrey

Andrey wrote:
Greetings to all the antenna experts here!

I want to create horizontally polarized antenna, low profile, located above
large ground plane. And I need it to be omnidirectional (sort of) and have
sufficient gain in horizontal plane.

My frequency of interest is 900 MHz. The ground plane is a roof of a car.

I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount it
above the ground plane.

Any ideas?

Thank you,

Andrey


Good Morning Andrey,

What you are proposing is not an easy task any horizontal antenna placed
close to a good ground plain is going to have most of it's signal at
90 degrees. ( Straight up) Until the antenna is at least 1/2 wave above
the ground plan. at that point it will start to show radiation to the
horizon. EZNEC shows max gain at 30 degrees to the horizon for a 1/2
wave horizontal dipole mounted 1/2 wave above perfect ground and the
pattern looks somewhat like a peanut shape. if you move the antenna up
to 1 fullwave length above the ground plain then the patern does not
change much but the elevation angle dose you then get a good lobe at 15
degrees and another at 45 degrees. hope this is of some help.
Dave kc1di

Thank you Dave,

for sharing with me results of your simulation. I got similar results. The
thing that works is slit pipe (Alford's slot, see
http://www.eta.chalmers.se/~pgp/alfo...lford_eng.html for example)

Pipe works over ground plane as well (not as well, beam gets lifted, stll
there is enough energy looking on the horizon). It is such a cumbersome
thing though - looks funny on car's roof. Not of ractical use.

And I still can not find anything else that does it.


Regards,

Andrey Gleener


"KC1DI" wrote in message
...
Andrey wrote:
Greetings to all the antenna experts here!

I want to create horizontally polarized antenna, low profile, located
above
large ground plane. And I need it to be omnidirectional (sort of) and
have
sufficient gain in horizontal plane.

My frequency of interest is 900 MHz. The ground plane is a roof of a
car.

I tried loops, from 50 to 300 mm diameter, radiation goes up if I mount
it
above the ground plane.

Any ideas?

Thank you,

Andrey


Good Morning Andrey,

What you are proposing is not an easy task any horizontal antenna placed
close to a good ground plain is going to have most of it's signal at
90 degrees. ( Straight up) Until the antenna is at least 1/2 wave above
the ground plan. at that point it will start to show radiation to the
horizon. EZNEC shows max gain at 30 degrees to the horizon for a 1/2
wave horizontal dipole mounted 1/2 wave above perfect ground and the
pattern looks somewhat like a peanut shape. if you move the antenna up
to 1 fullwave length above the ground plain then the patern does not
change much but the elevation angle dose you then get a good lobe at 15
degrees and another at 45 degrees. hope this is of some help.
Dave kc1di

Have you tried an halo or loop antenna? M2 Antenna's and Par Electronics makes
them. Homebrew plans are on the net.

The halo is a 1/2 wave dipole bent into a circle. Common designs use 1 turn,
but 3 turn halo's have been used, with more gain. Stacking 2 halo's also
provide additional gain. Weak signal operaters on VHF and UHF use them mobile
on a regular basis.

Randy ka4nma

"Theplanters95" wrote in message
...
Have you tried an halo or loop antenna? M2 Antenna's and Par Electronics
makes
them. Homebrew plans are on the net.

The halo is a 1/2 wave dipole bent into a circle. Common designs use 1
turn,
but 3 turn halo's have been used, with more gain. Stacking 2 halo's also
provide additional gain. Weak signal operaters on VHF and UHF use them
mobile
on a regular basis.

Randy ka4nma

Two points of clarification. The PAR design is not a half wave antenna. It
is longer than a half wave- that length combined with the isosceles triangle
shape yields an excellent omni pattern and a bit more BW

The 3 loop haloes were not 3 turns. The loops were configured as a folded
dipole in order to increase the inherently low feedpoint R (10-15 Ohms) of a
single loop. There is no increase in gain from doing this.

Dale W4OP

Hi Dale,

Are you saying that the old saturn halo was not 3 loops? It sure looks like it
in the pictures that I have seen.

I know that your design (the Par Omniangle) is not the classic 1/2 wave halo,
and does offer more advantages over a halo. I sure wish I had a 2m and 6m for
the upcoming VHF contest.

Randy ka4nma