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phase array: steering problem, help? - RF Cafe Forums
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| Mr.Sánchez
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Post subject: phase array: steering problem, help?
Posted: Tue Dec 23, 2008 2:46 pm
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Joined: Tue Dec 23, 2008
2:01 pm Posts: 2 Location: Madrid
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Hello, I've been working on a 1x8 linear
phase array. The antenna system is working perfect,
but I came across with a problem when making the
algorithms for steering. Imagine your phase
shifters give a maximum of 400º shift for a particular
frequency. Now suppose the required shifts for the
eight elements are for example: 0 90 180 270 360
450 540 630º. I programmed an algorithm
that used the periodicity of the signal so those
shifts are the same as: 0 90 180 270 360 90 180
270. I moduled all phase shifts to 360.
When testing the radiation pattern in a anechoic
chamber, the result was disturbing. I got a maximum
in the desired direction but the whole pattern was
very smooth, with less lobes that it should have,
much less directivity. Then we used another
algorithm that worked. Our phase shifter are switched
lines shifters, so in this new algorithm we worked
with temporal retards instead of thinking of degrees.
The thing is... it works. Then my question
is, why doesn't it work moduling the shifts to 360?
shouldn't the pattern be the same?? I'll
be thinking about it, thanks a lot in advance
--- i'll see you guys around, i'm new
in this world (1 year working after finishing college)
and i love these forum where you can share information
and knowledge.
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maxwelltesla |
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Post subject: Phase Shifter
Posted: Fri Jan 16, 2009 4:09 pm
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Joined: Thu Jun 24, 2004
3:10 pm Posts: 4 |
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What frequency are you working? Type of phase shifter...
MEMS?
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Mr.Sánchez |
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Post subject: phase array
Posted: Mon Jan 19, 2009 12:39 pm
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Joined: Tue Dec 23, 2008
2:01 pm Posts: 2 Location: Madrid
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i'm working from 2 to 6 GHz, and with switched lines.
if you can help me, I'd be glad to explain to
you my doubt in more detail, although I think it's
more or less clear my problem. Thanks
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karthik |
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Post subject: Re: phase array: steering problem, help?
Posted: Mon Jan 04, 2010 10:59 pm
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Joined: Tue Apr 11, 2006
8:13 pm Posts: 34 |
I dont know if you were able to solve your problem.
If you did, could you please post your finding?
If not, I have a couple of questions/suggestions:
1. Can you compare the time delay (which worked)
to the phase (which did not work). 2. You can
measure the phase that is actually being set - measure
the phase from the antenna element to the output
of the combiner - and ensure that the phase relationship
between adjacent elements is what you expect.
From your description, it appears the phase
(and/or amplitude) relationship between the elements
is not what you had calculated.
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fred47 |
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Post subject: Re: phase array: steering problem, help?
Posted: Sat Jan 23, 2010 12:08 am
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| General |
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Joined: Wed Feb 22, 2006
3:51 pm Posts: 106 |
If the antenna elements were isolated from each
other, the phase shifter and the time delay approaches
would in fact give the same result. But...
Antenna elements couple to each other, which
changes the driving point impedance, and a transmission
line further transforms the impedance. Summary:
Phase shifters can work, but you have to take inter-element
coupling into account. Good Luck!
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biff44 |
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Post subject: Re: phase array: steering problem, help?
Posted: Sat Feb 06, 2010 10:23 am
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Joined: Wed Apr 08, 2009
11:07 am Posts: 34 |
This is a trivial point, and I hessitate to bring
it up. But you do realize that a "switched line"
phase shifter, set into any one position, will have
a wildly different phase shift at each and every
frequency over the 2 to 6 GHz band. For instance,
if you dialed in 180 degrees at 2 ghz, if you touched
nothing but simply swept the frequency to 4 GHz,
you should get 360 degrees out of it (I am assuming
you de-embedded the measurement to right at the
switches in the switched line phase shifter, and
that the switched lines were all less than a wavelength
in length). If you use software that recognizes
the actual time delay switched in for each of the
switched lines, then that software will take into
account the frequency and calculate the true phase
shift at that one
frequency.
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biff44 |
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Post subject: Re: phase array: steering problem, help?
Posted: Sat Feb 06, 2010 10:33 am
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Joined: Wed Apr 08, 2009
11:07 am Posts: 34 |
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The more I think about this, the more I wonder what
the absolute phase shift is of each of your 8 phase
shifters, vs setting and frequency. A phase shifter
chip, for instance, might have tight specifications
for the relative
phase shift from one setting to another. But if
you measured the absolute phase shift of chip #1,
vs. chip #7 that might have been manufcatured 6
months later, I think all bets are off!
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Posted 11/12/2012
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