I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Thanks in advance for any insight!
Dave

"David Harper" wrote in message
om...
I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Thanks in advance for any insight!
Dave

Dave,

Actually phased arrays have existed in commercial broadcasting AM (day/night
patterns) as well as some FM.

The best way for you to visualize a phased array is to have 2, 3 or 4 stones
hit the water at the same time ....
you will see patterns emerge as cancellations happen.

http://home.earthlink.net/~jimlux/radio/antenna/phased/

http://mitglied.lycos.de/radargrundl...n/at18-en.html

Recent IEEE seminar
http://www.ieee-boston.org/edu/course_phased-array.htm

Hundreds of references available with a simple google search.

w9gb

On 12 Jun 2004 16:43:35 -0700, (David Harper)
wrote:

Hi Dave,

By the points asked:
how do the other side lobes get reduced and/or eliminated?
Through the addition or subtraction of phase;
Are the individual antenna transmitters/elements not omnidirectional
themselves?
This is not an imperative of design;
If not, what are the characteristics of their patterns?
They add or subtract according to phase offered;
how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.
How indeed, they are not immune from these issues.

Phase and distance are co-equivalent when you speak of multiple
sources. When one source excites resonant elements, those element's
create a phase lag/lead and combine with the original signal with a
phase lag/lead that is correlatable to physical separation from the
exciting source. The designer conspires to arrange all such
times/distances/lags/leads/phases to combine additively/subtractively
to create the desired pattern. Simple patterns like the figure 8 of
the dipole involve few components, but also reveal broad
characteristics for the same reason.

If you want a sharp beam with small fringing lobes, you have to invest
in quite a few times/distances/lags/leads/phases elements. Complexity
does not bring order easily. However money might. Those who build
radars are used to just such a lubricant. The dishes you see offer a
continuum of times/distances/lags/leads/phases with the added benefit
of fairly good shielding from a lot of their sources of grief.
However, they are constrained by physical necessity of being pointed
towards the area of interest.

Other radar designers using phased array sources, use massive
parallelism. Look at a picture of the USS Enterprise. Nearly the
entire surface area of the Island is radiating elements on all four
sides. Each and every source offers a very simple characteristic with
a variable delay line between it an free space - and of course, there
is some distance involved between each element and the next. Given
that those delay lines are addressable and individually setable, beam
steering is obtained through a rather simple concept.

If I recall my former trade correctly, some of the sources in the
array can be employed separate to the main combination - sort of like
picture-in-picture technology. :-)

73's
Richard Clark, KB7QHC

"David Harper" wrote
I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Thanks in advance for any insight!

=============================

To understand how things work it is necessary to be familiar with elementary
trigonometry. Its quite simple really.

Without trigonometry you just have to accept that's the way things are.

On 12 Jun 2004 16:43:35 -0700, (David Harper) wrote:

I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

There's really nothing special about a phased-array antenna.
It is a radiating aperture, just like the mouth of a horn
or the front of a parabolic "dish". The only difference
is that the phase and amplitude of the excitation across
the aperture can be much more finely adjusted to "squint"
the beam.

But the essential tradeoff remains: the larger the aperture,
the narrower the beam. And, like horns and reflectors, one
can reduce the sidelobes by not exciting the outside elements
as strongly, but with a corresponding reduction in gain from
the maximum obtainable for a given aperture size. This is
called illumination tapering and is done on all antennas
in one form or another to work the gain/sidelobe tradeoff.

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Most radars go for wider beams with lower sidelobes because
the overall system performance is better. But the sidelobes
are only reduced, not eliminated entirely.

Oh, yeah, and about the patterns of the individual elements,
they have to be as non-directional as possible. The deal is
that the overall antenna pattern is the result of the PRODUCT
of the array factor with the pattern of the individual elements.
If the individual elements have reduced gain off boresight, the
entire antenna gain is reduced off-boresight as well, limiting
the angles at which the beam may be "squinted".

Jim, K7JEB

Phased arrays are fun to play around with (on the 2-meter band especially)
You can experiment using physically manageable components.
You can switch elements phasing by using different lengths of feedline
its interesting - a good hobby in a hobby

"David Harper" wrote in message
om...
I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Thanks in advance for any insight!
Dave


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"Reg Edwards" wrote in message ...
"David Harper" wrote
I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Thanks in advance for any insight!

=============================

To understand how things work it is necessary to be familiar with elementary
trigonometry. Its quite simple really.

Without trigonometry you just have to accept that's the way things are.

Being an engineer, I am quite familiar with trigonometry. I believe
you didn't fully understand my question: How do the other side lobes
get reduced and/or eliminated? Theoretically, in some phased array
antenna configurations, some lobes have an undesirably high a gain. I
was wondering what filters / engineering work arounds were used to
mitigate this. Other posts have adequately answered this question,
however. Thanks anyway.

"David Harper" wrote in message
om...
"Reg Edwards" wrote in message
...
"David Harper" wrote
I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Thanks in advance for any insight!

=============================

To understand how things work it is necessary to be familiar with
elementary
trigonometry. Its quite simple really.

Without trigonometry you just have to accept that's the way things are.

Being an engineer, I am quite familiar with trigonometry. I believe
you didn't fully understand my question: How do the other side lobes
get reduced and/or eliminated? Theoretically, in some phased array
antenna configurations, some lobes have an undesirably high a gain. I
was wondering what filters / engineering work arounds were used to
mitigate this. Other posts have adequately answered this question,
however. Thanks anyway.

David

I'd submit that your question is very difficult to explain within the
consraints of a newsgroup paragraph or two in a news group. The subject of
aperature distribution has been studdied for years and years by thousands
of high level engineers.
Although it is desired to minimize the sidelobe level from scanning flat
phased arrays, there is a limit to how low the sidelobes can be made. They
sure dont go to zero.
A side looking scanning antenna of phased elements will have individual
elements who's pattern is appropriate for whatever area is being scanned.
The pattern from each element wont be omnidirectional.

It might be a good exorcize for you to draw a plot on a piece of paper
with 10 antennas in a row. You can quickly see that the array will have max
gain at some power distribution and have sidelobes that change appreciably
when the distribution of power (and phase) is varied over the length of that
array.

Jerry

K7JEB wrote in message . ..
On 12 Jun 2004 16:43:35 -0700, (David Harper) wrote:

I had a simple question in regards to phased array antenna patterns.
If a phased array is trying to send a narrow beam in a specific
direction, how do the other side lobes get reduced and/or eliminated?
Are the individual antenna transmitters/elements not omnidirectional
themselves? If not, what are the characteristics of their patterns?

There's really nothing special about a phased-array antenna.
It is a radiating aperture, just like the mouth of a horn
or the front of a parabolic "dish". The only difference
is that the phase and amplitude of the excitation across
the aperture can be much more finely adjusted to "squint"
the beam.

But the essential tradeoff remains: the larger the aperture,
the narrower the beam. And, like horns and reflectors, one
can reduce the sidelobes by not exciting the outside elements
as strongly, but with a corresponding reduction in gain from
the maximum obtainable for a given aperture size. This is
called illumination tapering and is done on all antennas
in one form or another to work the gain/sidelobe tradeoff.

I ask this because I'm trying to understand how tracking radars can
send narrow beams in the desired direction without significant
secondary lobes to interfere with returns from the desired lobe.

Most radars go for wider beams with lower sidelobes because
the overall system performance is better. But the sidelobes
are only reduced, not eliminated entirely.

Oh, yeah, and about the patterns of the individual elements,
they have to be as non-directional as possible. The deal is
that the overall antenna pattern is the result of the PRODUCT
of the array factor with the pattern of the individual elements.
If the individual elements have reduced gain off boresight, the
entire antenna gain is reduced off-boresight as well, limiting
the angles at which the beam may be "squinted".

Jim, K7JEB


Thanks! You know any simple phased array configurations that are easy
to mathmatically model? I've played with a 4-element array all
located on the same axis just for fun to see what resulted (and to
make sure my equations were right), but I'd like to find some
real-world systems (hopefully without too many elements) to play with.
Any digrams exist on the net? (dimensional relationship between
elements, etc).

Thanks again!
Dave

It might be a good exorcize for you to draw a plot on a piece of paper
with 10 antennas in a row. You can quickly see - - - -

=============================

In other words - trigonometry! Or geometry!