Antenna array elements distance problem

[sbhalerao]

Antenna array help!!!!

Hi to all,
I am a part of a research group that's presently designing a antenna array - The real catch is that we want the size to be as small as possible... WE decided to settle for folded patch antenna (size λ/16) - though this would mean that we get a gain of 0.3 dBm...
The problem now is-- In almost all the thory books on antennas , its mentioned that elements in a antenna array must be separated by λ/2 distance..
Firstly, is it electrical distance or physical distance??? (the patch can be coiled / so these may be different)

In Thomas Milligan (Modern Antenna Design), its stated " Elements if separated by a lesser distance than will block radiation from other elements"...
I think "they do not block" - its just a case of superposition of the fields from the antenna elements - the resultant field is just the superposition of the fields due to individual antennas( which could be represented by dipole....). So if the distance between elements is less, but the elements are appropriately arranged so that fields do not cancel out or something ( no doubt there will be some loss of radiation - but this may be optimised),....
For our application, size is the most important parameter and we are working on 2.4 GHz ... I am going to simulate the above using IE3D and Empire , but I wanted to know if there's some fallacy/glitch in my scheme...

Thanking you all in advance..
Shantanu Bhalerao

 

[plasma]

Re: Antenna array help!!!!

Hi sbhalerao

You right "they do not block" just match the impedance of your array including the mutual coupling and the surface waves coming from the edge of the array. if you succeed doing it you will get no loss in gain.

don't forget if you decrease the distance between elements you get smaller area
and that's lead to lower Gain.
The Gain dependable on the size of the antenna area.

PL

 

[mhadidy2005]

UWB Reply

Dear,,

This is a very nice paper for uwb antenna array

Regards,
Mohamed

 

[jian]

Re: Antenna array help!!!!

Hi, Shantanu:

I don't think there is any blocking. However, when two elements are close, the coupling always tries to suppress (or reduce) the radiation from the individual elements. You need fine tuning it in order to achieve best results.

Also, when two elements are close, it is not pure superposition. There is some interaction related to the correlation of the individual fields. If you look at the Poynting vector, you will see. Assuming antenna A1 is creating E1 and H1 and antenna A2 is creating E2 and H2 individually. The radiated powers are:

Pr1 = integral{ E1*Conj(H1) }
Pr2 = integral{ E2*Conj(H2) }

while their input powers are Pi1 and Pi2.

Assume you put them together and the coupling does not change the current distribution, you will have the input power as:

Pi = Pi1 + Pi2

However, the radiated power is:

Pr = integral{ (E1+E2)*Conj(H1+H2)}
= Pr1 + Pr2 + Pra1 + Pra2

Pra1 = integral{ E1 * Conj(H2) }
Pra2 = integral{ E2 * Conj(H1) }

If you further assume A1 and A2 are identical and they are moving to the same location, you will see, Pr1 = Pr2 = Pra1 = Pra2. In the other word, Pi = 2 * Pi1 while Pr = 4 Pr1. As you can see, the input power is doubled while the radiated power is quadrupled. Such a case is impossible. What it indicates is that when you put 2 elements close to each other, they will affect the current distribution of each other. If you still use superposition for such an analysis, you will over predict the radiated power. Certainly, when the coupling between the elements are far away, you can use superposition to get reasonable accurate results.

Best regards.