Theroretical antenna question
 

Is it possible to build an omnidirectional receiving antenna with
gain?

Let us assume an ideal dipole Call it 0dBd

Now let us build two ideal dipole antennas and combine their outputs
we have an antenna with possibly twice the received energy or 3dBd
gain.

Now for signals from certain orientations we signals canceling in
phase for less than 0dBd gain....



Is it possible to build an antenna with more capture area, giving
gain,
without adding directivity?


Thought experiment saying it is possible......
Cover a 1 meter sphere with solar cells......

Cover a 100 mete sphere with solar cells......
It's clear that the 100 meter sphere would gther more energy than the
1 m sphere.... thus it seams it would be possible,

No what forms would an isotropic (Or at lease hemispherical) pattern
antenna with gain 0 dBi look like?


Paul (Kl7JG)

wrote:
Is it possible to build an omnidirectional receiving antenna with
gain?

Of course, the Aug. 2003 QST has some of them on page 19 & 108. The
Comet GP-24 for 2.4GHz is twenty end-to-end 1/2WL antennas.
--
73, Cecil http://www.qsl.net/w5dxp



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Sometimes "omnidirectional" means "equally radiating in all azimuth
directions", which is the interpretation Cecil has used. In that case,
yes, of course, you can achieve gain by concentrating the power in the
vertical direction, i.e., increasing the power density at some elevation
angles at the expense of others. A collinear antenna (linear antennas
placed end-to-end as Cecil describes) is a common way of achieving that.

I inferred from the original posting that the intended meaning was truly
omnidirectional, as in isotropic, the same in all directions in three
dimensional space. If that's correct, the answer is no.

The explanation in my response was in terms of a transmitting antenna.
It's well established (the reciprocity principle) that the gain of an
antenna is the same for transmitting and receiving, so the conclusion is
equally valid for a receiving antenna.

Roy Lewallen, W7EL

W5DXP wrote:
wrote:

Is it possible to build an omnidirectional receiving antenna with
gain?


Of course, the Aug. 2003 QST has some of them on page 19 & 108. The
Comet GP-24 for 2.4GHz is twenty end-to-end 1/2WL antennas.

Roy Lewallen wrote:
If by omnidirectional you mean truly the same in all directions, up,
down, and in azimuth, the answer is no.

From the IEEE Dictionary:

"omnidirectional antenna - An antenna having an essentially non-
directional pattern in a given plane of the antenna and a directional
pattern in any orthogonal plane. Note: For ground-based antennas, the
omnidirectional plane is usually horizontal."

"isotropic radiator - a hypothetical, lossless antenna having equal
radiation intensity in all directions."
--
73, Cecil http://www.qsl.net/w5dxp



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Paul,
If you mean 'omnidirectional' in the commonly used
fassion of ham radio, then the answer is yes. If you
mean 'omnidirectional' as in an isotropic antenna, then
no. To date, and to the best of my knowledge, I have
never used an isotropic antenna, nor have I ever heard
one used. So, I guess the answer is yes...
'Doc

So do you suppose the original poster has an IEEE dictionary?

Roy Lewallen, W7EL

W5DXP wrote:
Roy Lewallen wrote:

If by omnidirectional you mean truly the same in all directions, up,
down, and in azimuth, the answer is no.


From the IEEE Dictionary:

"omnidirectional antenna - An antenna having an essentially non-
directional pattern in a given plane of the antenna and a directional
pattern in any orthogonal plane. Note: For ground-based antennas, the
omnidirectional plane is usually horizontal."

"isotropic radiator - a hypothetical, lossless antenna having equal
radiation intensity in all directions."

I was implying iostropic in 3 dimensions....

Now for a paradox.....


If RX==TX as for as antenna gain

And 100W is 100W.... then isotropic had dBi =0 be the laws of
conservation of energy.....


No suppose we have an antenna that captures all of the energy passing
though a 1M square.......

Now make that a 10M square.....


Clearly a 10M "Fishing net" can capture more than a 1M net, but

Then RXgain != TXgain


So what gives where is this wrong?

Roy Lewallen wrote:
So do you suppose the original poster has an IEEE dictionary?

If he used to have $120. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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What relative gain do you think the two antennas have?

Are you still talking about isotropic antennas, or have you moved on to
accommodate other patterns?

How do you conclude that the receiving gain of your hypothetical antenna
is different from the transmitting gain?

Roy Lewallen, W7EL

wrote:
I was implying iostropic in 3 dimensions....

Now for a paradox.....


If RX==TX as for as antenna gain

And 100W is 100W.... then isotropic had dBi =0 be the laws of
conservation of energy.....


No suppose we have an antenna that captures all of the energy passing
though a 1M square.......

Now make that a 10M square.....


Clearly a 10M "Fishing net" can capture more than a 1M net, but

Then RXgain != TXgain


So what gives where is this wrong?

AHA!!! Now you found your IEEE dictionary!
--
Crazy George
Remove NO and SPAM from return address
"W5DXP" wrote in message
...
Roy Lewallen wrote:
If by omnidirectional you mean truly the same in all directions, up,
down, and in azimuth, the answer is no.

From the IEEE Dictionary:
snip