On Mon, 31 Oct 2016 09:59:24 +0000 (UTC), unk wrote:


Frequency is 2.4 ghz, plane is made from radials about 4x wavelength
(can't change this), and I can place a monopole antenna anywhere up to
about 5 wavelengths away (up) from the center.

This might help. It's the NEC plots of a vertical dipole above an
infinite ground plane:
http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html
http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html

Suggestion: Lose the 1/4 wave monopole and replace it with a 1/2 wave
dipole.

I would like to maximize reception[1] in the angles close to the ground
plane (~30 degrees) and/or minimize the null at 90.

There will always be a hole directly above the vertical dipole. You
can minimize it to within a few degrees, but directly overhead will
have no signal. I've had to deal with this on 1090MHz avionic
antennas by using two isolated antennas and combining the signals. For
near the horizon, an AMOS/Franklin vertical dipole. For overhead, a
turnstile. I haven't tried it on 2.4Ghz.

Can I shape the pattern by appropriate placement of the antenna?

No. If you want lots of gain at the horizon, you're not going see any
gain directly above the antenna.

[1] yes reception; this is for a radio application pretty far from normal
amateur radio (rc control of a flying vehicle - so the antenna will
actually be mounted *below* the ground plane), but

Most of these use patch/panel antenna arrays. Lots of gain, but you
have to track the flying machine somehow (usually manually).

a) there will also be telemetry in the opposite direction using the same
antenna; and

Telemetry and video are usually done on 5GHz using tiny turnstile
antennas.

b) the rc guys don't know **** about antennas, it's all "I bought this
one and it worked great"

No comment. I've seen much the same thing. The limiting factor with
RC is usually the antenna on the drone or whatever. Getting a decent
pattern is difficult so they resort to hemispherical or half
hemisphere antennas. This results in lousy gain, but works when doing
aerobatics and inverted. That puts the load on the ground antenna
system, which in my never humble opinion, can only be done effectively
with a high gain antenna (not too high) and tracking/pointing.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558