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FM antenna matching using HFSS

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paujuan

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Hi all,
I am designing a VHF small antenna using HFSS. Since it is a narrow-band antenna, I need to simulate the matching network to maximise the received power. Do you know what is the best way to do that, once I have the S11, Z11 and Y11 parameters?
Thank you.
 
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Hi,

What kind of FM antenna do you want to model? The matching network can be simulated separately once the antenna impedance as a function of frequency has been obtained.
 
Hi kekosat300,
Thanks for your reply.
I need a planar FM antenna, so I think a spiral antenna wil be the best option (although I want to simulate more than one structure). However, I think it is not possible to compare two different radiation patterns obtained at different adaptation rates, so that's why I need to ensure my antenna is adapted for each geometry (please, correct me if I am wrong!)
 

What do u mean by saying "adaption rates"?
 

Hi,
I mean that to compare two different designs, I need to ensure that both are simulated under the same adaptation conditions. That is, is I have an antenna with |s11|=-6 dB and another with |s11|=-12 dB, the radiation patterns will be obviously different, so I must reach a real admittance to compare both antennas. What is the best way to accomplish that?
Thank you.
 

The radiation pattern (i.e. gain/directivity) calculated by HFSS does not change with S11. S11 stands for the impedance matching performance, which is another paramter different from far-field gain/directivity.
 

Hi streamlet,
First of all, thank you for your reply. Clearly, you understood my doubt.
Do you really think that s11 and Gain are calculated independently in HFSS? I don't know if it is possible, since the Gain parameter is calculated by means of the initial power, so it is affected by the mismatch between the source and the antenna. In fact this is just the fact that I need to clarify. I just thought that to obtain the radiation pattern, the antenna might be perfectly matched.
Thank you!
 

The radiation pattern (i.e. gain/directivity) calculated by HFSS does not change with S11. S11 stands for the impedance matching performance, which is another paramter different from far-field gain/directivity.

The Gain/directivity change with S11. If you have a poor Impedance matching you will never have a good gain/directivity and vice versa. So you cant say that radiation pattern ll not change w.r.t S11.

@Poujan....Spiral antenna is not a planar antenna.

/SC
 

The Gain/directivity change with S11.

I am not an HFSS user, but for the EM simulators that I have, gain can be calculated both ways: with or without the "loss" from S11.
For directivity, that refers to the total radiated power anyway, so it is independent of S11.
 

I am not an HFSS user, but for the EM simulators that I have, gain can be calculated both ways: with or without the "loss" from S11.
For directivity, that refers to the total radiated power anyway, so it is independent of S11.

You are trying to say that without having a Good impedance Match at the antenna input,you will be able to have a High Directivity?????? For instance,if you have a poor impedance match at the antenna input, what ll be the radiated power from it?? and this radiated power ll be the same if there is a perfect impedance match at the antenna input? Your claim doesnt make sense!!!
/SC
 

You are trying to say that without having a Good impedance Match at the antenna input,you will be able to have a High Directivity??????

Yes. Just get an antenna textbook and look at the definition of directivity.
 

Yes. Just get an antenna textbook and look at the definition of directivity.

I know the definition of directivity very well. My question is impedance matching ll not effect the power which ll be radiated from the antenna ????? are you trying to say this ????
 

impedance matching does of course impact the radiation of the antenna, this is known as radiation efficiency. directivity and gain are related by this efficiency. so i think what volker is trying to say is, and correctly say, is that directivity should be not impacted by your poor match, however gain will. in other words, the shape of your radiation pattern should stay generally the same between directivity and gain, while the amplitude will change.

gain = directivity X efficiency (essentially)
 
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impedance matching does of course impact the radiation of the antenna, this is known as radiation efficiency. directivity and gain are related by this efficiency. so i think what volker is trying to say is, and correctly say, is that directivity should be not impacted by your poor match, however gain will. in other words, the shape of your radiation pattern should stay generally the same between directivity and gain, while the amplitude will change.

directivity = gain X efficiency (essentially)

Exactly that was what i have written that Gain/directivity ll get effected due to S11 or poor match.

---------- Post added at 20:08 ---------- Previous post was at 20:05 ----------

directivity = gain X efficiency (essentially)


Isnt it like:

Gain=efficiencyxdirectivity.

???
 

so i think what volker is trying to say is, and correctly say, is that directivity should be not impacted by your poor match, however gain will.

Exactly.

And because of that, the method described above in post #6 works fine: you can design the antenna for directivity first, without worrying about the input matching, and then match the antenna later.

Regarding gain, as stated above, many EM simulators have two gain definitions: gain relative to the available input power (incident wave) and gain relative to the accepted power (incident minus reflected).
 
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Exactly that was what i have written that Gain/directivity ll get effected due to S11 or poor match.

---------- Post added at 20:08 ---------- Previous post was at 20:05 ----------




Isnt it like:

Gain=efficiencyxdirectivity.

???

yes edited, typing fast and typoed, thanks.
 

Yes, I am pretty sure about that. The following is the definition of gain quoted from online help of HFSS v12, note the words marked in bold:
Gain is four pi times the ratio of an antenna’s radiation intensity in a given direction to the total power accepted by the antenna.
 

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