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phase array: steering problem, help? - RF Cafe Forums

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Mr.Sánchez
 Post subject: phase array: steering problem, help?
Posted: Tue Dec 23, 2008 2:46 pm 
 
Lieutenant

Joined: Tue Dec 23, 2008 2:01 pm
Posts: 2
Location: Madrid
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.


 
   
 
maxwelltesla
 Post subject: Phase Shifter
Posted: Fri Jan 16, 2009 4:09 pm 
 
Lieutenant

Joined: Thu Jun 24, 2004 3:10 pm
Posts: 4
What frequency are you working? Type of phase shifter... MEMS?


 
   
 
Mr.Sánchez
 Post subject: phase array
Posted: Mon Jan 19, 2009 12:39 pm 
 
Lieutenant

Joined: Tue Dec 23, 2008 2:01 pm
Posts: 2
Location: Madrid
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


 
   
 
karthik
 Post subject: Re: phase array: steering problem, help?
Posted: Mon Jan 04, 2010 10:59 pm 
 
Colonel

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.


 
   
 
fred47
 Post subject: Re: phase array: steering problem, help?
Posted: Sat Jan 23, 2010 12:08 am 
 
General
User avatar

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!


 
   
 
biff44
 Post subject: Re: phase array: steering problem, help?
Posted: Sat Feb 06, 2010 10:23 am 
 
Colonel

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.

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com


 
   
 
biff44
 Post subject: Re: phase array: steering problem, help?
Posted: Sat Feb 06, 2010 10:33 am 
 
Colonel

Joined: Wed Apr 08, 2009 11:07 am
Posts: 34
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!

_________________
Rich
Maguffin Microwave Consulting
www.MaguffinMicrowave.com





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