Mutual Coupling between Dipole Antennas

[sweetchoto]

Dear All,

Kindly see the attached HFSS file,it contains two separate Designs. One is of 'single Half-wavelength Dipole' operating at 2.4 GHz. This design is perfectly fine and giving the results as expected. The other second design consist of 3 Identical Dipoles(operating at 2.4 GHz), The Dipole at centre is acting as Receiver(Rx) whereas the Dipoles at each end are acting as Trasmitters(Tx). One Transmitter(Dipole) is placed at distance 'D(any distance)' from Receiver(Rx) and Second Transmitter(Dipole) is placed at a distance 'D+Lamda/2' where Lamda is calculated using 2.4 GHz. Then, the effect of these two transmitters on Receiver antenna is plotted by using the simple equation of

Coupling= (S(1,2)+S(1,3)) dB

Here 2,3 denotes the transmitter dipoles and 1 denotes the receiver dipole in centre and i gave it the name Coupling.


In principle, what i should get is a Null at 2.4 GHz at receiver antenna location due to the cancellation of transmitting signals of the two transmitter dipoles since they are placed at such distances from receiver antenna that their signals will reach at the receiver out of phase and cancel each other out. But in my simulation result,i get the opposite of it. Instead of getting a Null at 2.4 GHz i get a peak. Kindly see the attached file what i have done and if someone could give me any idea as what to do or what i am doing wrong. I will be thankful to him.

Looking forward to hear some sensible comments.

/SC

 

[zorro]

Hi,

can you post images (instead of hfss file)?
Regards

Z

 

[sweetchoto]

Hi,

See the attached images.

/SC

 

[sweetchoto]

The Last 2 Images are for the 3 dipoles and the Resultant Graph from the equation which i have described in my first post.

/SC

 

[zorro]

Distances from antenna 1 to antennas 2 and 3 are not the same, so the amplitudes of the couplings are different. Cancellation is not good.
Resonance of the dipoles makes that both couplings increase near resonance.
I would expect that if you increase sufficiently the distances, conserving the lambda/2 difference, a partial cancellation starts to be observable.
If both distances are the same but the dipoles 2 and 3 are fed with opposite phases, cancellation must be total.
Regards

Z

 

[sweetchoto]

Hi Zorro,

I agree with what you said. I already tried to play with the amplitudes (tried to reduce the amplitude of the antenna which is closer to centre antenna compared to the other one) but still it does not effect the graph that much. I did what you suggested, i placed antennas 2 and 3 at equal distance from antenna 1 in centre and fed antenna 2 with 180 degree out of phase signal compared to antenna 3 but the graph stays the same as i have posted previously with no total cancellation observed even then which is totally insane.
That is why i have posted my HFSS file in case i am setting up anything wrong but i have checked it number of times and everything is ok. any other idea ?
/SC

 

[sweetchoto]

Anybody any idea. Em still stuck with it. ?????

 

[zorro]

I did what you suggested, i placed antennas 2 and 3 at equal distance from antenna 1 in centre and fed antenna 2 with 180 degree out of phase signal compared to antenna 3 but the graph stays the same as i have posted previously with no total cancellation observed even then which is totally insane.

Are you sure that you are adding correctly S12 and S13 (i.e. with right amplitudes and phases)?
Z

 

[sweetchoto]

hi Zorro,

Yes. both antennas are at equal distance from centre antenna so i am feeding both of them with equal amplitude and opposite phases. I am using 'edit sources' option for this and setting the 'scaling Factor' (which is related to amplitude) for both antennas to '1' and 'Phase offset factor' (which is related to phase) to '0 degree' for antenna 2 and '180 degree' for antenna 3 which means antenna 3 is fed by signal of equal amplitude but oppostie phase as compared to signal of antenna 2.

If there is anything wrong in this kindly correct me. So far by doing this i achieve nothing conclusive. Graphs of coupling are the same(in shape) like i posted before with minor change in amplitude which is not so significant. What i was expecting to get was a NULL at 2.4 GHz which is not happening.

 

[sweetchoto]

Hi Zorro,

I have fixed the first thing. I was feeding antennas in wrong way thinking that 'Edit sources' ll do the trick. But now i have fed the antenna 2 and 3 with equal amplitude and opposite phase manually in HFSS while they are at equal distance from receiver antenna. I see the total cancellation as you said and a NULL is observable. But when i move the antenna 3 at distance 'D+Lamda/2' then the results gets strange. I will keep trying to fix it.

/SC

 

[sweetchoto]

Hi Zorro,

I have solved it with results as expected

/SC

 

[zorro]

Well!
How was then the solution?
Regards

Z