Array Radiation Pattern

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mprathap

Joined: 27 Apr 2007
Posts: 25
Helped: 1

18 Sep 2008 19:35 Array Radiation Pattern

I am kind of confused about generating radiation patterns in an Array. I have 2 antennas and I have defined two ports, one for each. For which port is the radiation pattern calculated with respect to? How do I generate patterns for both the ports at the same time. Or specifiy with respect to which port I need the radiation pattern calculated.

I am not interested in the radiation pattern of the whole structure as such. I want to see the individual patterns of each element with the other element present.

Thanks in advance.

burton

Joined: 12 Dec 2003
Posts: 184
Helped: 8

18 Sep 2008 22:54 Re: Array Radiation Pattern

You can excite only one port, and other port is not excited.

mprathap

Joined: 27 Apr 2007
Posts: 25
Helped: 1

19 Sep 2008 16:25 Re: Array Radiation Pattern

If you read my question carefully, you will see that I have already figured that out.

But what I need to know is how do I select which port is excited?

Thanks.

juppydu

Joined: 05 Jul 2004
Posts: 65
Helped: 11

21 Sep 2008 9:42 Re: Array Radiation Pattern

Your question is not clear,

you have two antennas, two ports, so you can calculate both individual pattarn or the whole array pattern.. what is the question ?

please specify better what you are looking for.. so we can help you !

cuongtran

Joined: 06 Feb 2007
Posts: 161
Helped: 4
Location: WhiteHouse

25 Sep 2008 10:50 Array Radiation Pattern

HI, it s sure that the excited antenna you shoud see its RP.

mprathap

Joined: 27 Apr 2007
Posts: 25
Helped: 1

29 Sep 2008 22:22 Array Radiation Pattern

juppydu,

yes I have 2 antennas each with a port defined on it. When I solve the system, do I get the whole array pattern or one of the individual pattern?

If I get an individual pattern, to which port is this pattern with respect to? And how do I specify with respect to which port I want the pattern to be calculated?

If it is an array pattern, then is there a way to get the individual pattern without shedding one of the two ports?

Hope this is more clear now.

Zottiri Kusuta

Joined: 02 Sep 2005
Posts: 61
Helped: 8

30 Sep 2008 0:42 Re: Array Radiation Pattern

Which simulation tool are you using?

When you set up your ports, there should be a setting for the voltage/current excitation magnitude and phase. for example, if you set one of the ports to 1V and the other one to 0V, then you get mostly the radiation pattern of the excited one (the one with 1V)... Note that, if your antennas are close to each other, even if you don't excite one of the antennas, there will be induced currents on that antenna because of mutual coupling, and that antenna will radiate also, parasitically. Therefore the radiation pattern in this scenario, theoretically, can not be the radiation pattern of a single antenna. If your un-excited antenna is far from the other one, or if you just delete this antenna, then of course you get the radiation pattern of your actual antenna.

If you want to find an antenna array radiation pattern when both antennas are excited, you need the specify the excitation voltages/currents for both antennas. Then, what you see will be the array radiation pattern.

In some simulation programs, you can only simulate one antenna, and then you can use the built-in array factor calculator to find the whole array radiation pattern. In my knowledge, this works when the mutual couplings are negligible, and therefore array theory is valid.

mprathap

Joined: 27 Apr 2007
Posts: 25
Helped: 1

30 Sep 2008 1:01 Re: Array Radiation Pattern

Kusuta,

Thanks for your input.

I am using HFSS. I believe you cannot set the voltage/phase when you work with waveport/ lumped ports in HFSS, though I might be wrong.

The bigger picture is this: I have an array of antenna elements aligned in a straight line. And I want to see the radiation patttern of each element in the presence of the other antenna. Each antenna has a port defined on it.

What I am not sure is, when I analyze the structure in HFSS, whose radiation pattern do I get out of those say N elements in the array. I am trying to figure out a way to extract the radiation pattern for each element.

So I need to find the radiation pattern of one antenna element in the presence of the others, i.e. the effect of mutual coupling on the radiation pattern. Yes, the other elements will have a parasitic radiation - but I am not interested in it. What I am interested in is the radiation pattern of the element under consideration + the parasitic radiation induced in it by the other elements in the array.

If my question isn't clear, please let me know. I will try to explain further.

Thanks a lot!

Zottiri Kusuta

Joined: 02 Sep 2005
Posts: 61
Helped: 8

30 Sep 2008 1:08 Re: Array Radiation Pattern

I see what you want...

I assume you know: HFSS -> Fields -> Edit Sources. Does anything happen to radiation pattern when you play with these sources?

BTW, by default the first port created is excited in HFSS, others are un-excited... Or only excited for S-parameter calculations but when fields are calculated etc., they are un-excited...

mprathap

Joined: 27 Apr 2007
Posts: 25
Helped: 1

30 Sep 2008 1:35 Re: Array Radiation Pattern

Kusuta,

I think you led me to what I was looking for.

I knew about HFSS -> Fields -> Edit Sources, but I did not pay too much attention to it. I tried to edit the power value, but it wouldn't let me. I did not have the patience to look at the dialog box for long enough to see that I can edit the scale factor and pick which element is excited.

Thank you very much. You made my day.

BTW, what would happen if I set to excite all the elements. Will give me the array radiation pattern? And what exactly is meant by the array radiation pattern? Is it just the superposition of all the resulting radiation patterns, or is there more to it?

And if it is the superposition I have another question too! (sorry for the long list of questions) Assume that the array size is much larger than the antenna wavelength. Then at what distance does this 'superposed' pattern become valid? I ask this because since the whole structure is now larger than lambda/4 which is usually taken as the start of the far field boundary, how does that concept extend to the array now?

Thanks a million!!

Zottiri Kusuta

Joined: 02 Sep 2005
Posts: 61
Helped: 8

30 Sep 2008 1:54 Re: Array Radiation Pattern

mprathap,

actually, array radiation pattern is defined by you: how you are to excite the antennas with different magnitudes and phases.

in simple terms, if you think of the array theory:

array radiation pattern = single antenna radiation pattern × array factor

all those spacings between antennas and excitations come into the array factor...

of course, your antennas are close to each other in your simulation, so you want the full wave simulation instead of array theory, but the idea is the same... as you say, array radiation pattern is the radiation pattern of the whole system with the excitations etc. you define... (not necessarily 1-1-1-..., but lets say 1-0-1*exp(-j*pi/3)...)

for the pattern to be a valid approximation, it has to be in the far field. to find that there is a formula for far field distance, take a look at balanis antenna book. there you will see an antenna aperture D, or sth like that: that is the maximum distance of all of your aperture (all your antennas). think it as a diameter of the smallest sphere that can enclose all your radiators....

note: by aperture size i mean the physical aperture size. do not confuse with the antenna aperture terminology, which is different...

Last edited by Zottiri Kusuta on 30 Sep 2008 2:00; edited 1 time in total

mprathap

Joined: 27 Apr 2007
Posts: 25
Helped: 1

30 Sep 2008 1:57 Re: Array Radiation Pattern

Thanks, I will look it up.

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