"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.

"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

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!

Below

One method of eliminating* sidelobes from an array is to use 1/2 lambda
element spacing and in-phase, binomial power distribution to the elements.

This has been done in FM broadcast transmit arrays to reduce radiation
levels on the ground immediately adjacent to the tower. Paper 5 at
http://rfry.org shows some of the considerations for its use. Paper 10 at
the same site is a slide show wherein slides 20 and 23 also deal with this.

R. Fry

* in free-space theory, anyway
____________

"David Harper" wrote
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.