Dipole antenna impedance matching at a frequency other than the resonant frequency

[srijan.rio]

Dipole antenna impedence matching at frequency other than resonant frequency

Hi all,

I have a confusion regarding impedance matching. Suppose I design a planar dipole antenna for 5 GHz and 50 ohm impedance.
Now if I want to use the same antenna at 1 GHz is it theoretically possible to match the input impedance of the same antenna @ 1 GHz and get good results in return loss and other parameters ?
Apologies if I am missing something obvious.

 

[FvM]

Re: Dipole antenna impedence matching at frequency other than resonant frequency

Supposed 5 GHz is the fundamental dipole frequency, the input impedance at 1 GHz will be mostly capacitive with a very small real part (radiation resistance). This means a matching circuit for 1 GHz can be implemented only with high Q respectively very small bandwidth.

 

[srijan.rio]

Re: Dipole antenna impedence matching at frequency other than resonant frequency

Thank you for your reply.
Ok so theoretically its possible then?
That means if I get the impedance result for the dipole with 5 GHz fundamental frequency for other different frequencies(say 1 GHz) by HFSS simulation, and set the terminal port impedance to that value, should the antenna resonate with same results at that particular frequency( 1GHz). Like should i get the same dip in return loss or it will be different.

 

[davenn]

Re: Dipole antenna impedence matching at frequency other than resonant frequency

Thank you for your reply.
Ok so theoretically its possible then?
That means if I get the impedance result for the dipole with 5 GHz fundamental frequency for other different frequencies(say 1 GHz) by HFSS simulation, and set the terminal port impedance to that value, should the antenna resonate with same results at that particular frequency( 1GHz). Like should i get the same dip in return loss or it will be different.

not likely

impedance matching is one thing, resonance is another. Its performance is likely to be dreadful

D

 

[biff44]

Re: Dipole antenna impedence matching at frequency other than resonant frequency

you CAN have a non resonating radiating structure. Like a small loop that is driven by a current source. It will be very inefficient though, but will work very broadband simply because you are not resonating it.

with a loop, you can just make it out of thick conductor and pump a LOT of RF current into it. For a electrically-short dipole, you would have to feed it with a very high RF voltage....which would probably be much less practical, and possibly dangerous to the user.

 

[c_mitra]

Re: Dipole antenna impedence matching at frequency other than resonant frequency

It all depends on the Q: if the antenna is low Q by design then it will have a small resonance even at 1 GHz. Of course efficiency will suffer but that is the price for having a broad band antenna.

 

[Azulykit]

Re: Dipole antenna impedence matching at frequency other than resonant frequency

If all you want is a match put an attenuator in series with the antenna. A -5 dB pad will result in a -10 dB or better s11. That is theoretically and practically possible but then as was mentioned above you will need a sense of humor about the performance otherwise.

Do you have a sense of humor?