Designing a complex impedance antenna

[sh4x]

hai, I'm NB in this area, and just want to ask whether is it possible to design a complex impedance antenna ( 3D antenna, not stripes one) ?

My idea is I want to get rid of the matching circuit that usually placed between the chip and the antenna....

I read that antenna it self has impedance and it is complex impedance, not only real impedance.... so, how can i calculate the impedance of an antenna? or can i know it by simulating using software ? which software is that?

thank you in advance.


Sh4x

 

[Wiley]

Re: Complex Antenna

The short answer is no. The real part of the antenna's impedance represents power lost, either to ohmic losses or radiation, and the imaginary part of the antenna's impedance represent power stored in the near field. When the input impedance has a strong imaginary part, power is not radiated by stored, and this would not be a good antenna.

Yes, you can design an antenna to match the chip's output impedance, but the antenna would not actually radiate much energy.

 

[bingjiang99]

Re: Complex Antenna

I don't agree with your point. I would like to say YES with conditions.

First, if power is radiated or dissipated and stored, ideally it would not affect the transmitting as long as it is matched.

Second, if the imaginary part is too big, it is going to be very difficult to match the antenna with your transceiver.

Third, you may want your transceiver to be used for general cases (antennas with 50 ohm ).

The short answer is no. The real part of the antenna's impedance represents power lost, either to ohmic losses or radiation, and the imaginary part of the antenna's impedance represent power stored in the near field. When the input impedance has a strong imaginary part, power is not radiated by stored, and this would not be a good antenna.

Yes, you can design an antenna to match the chip's output impedance, but the antenna would not actually radiate much energy.

 

[sh4x]

Re: Complex Antenna

hummm , and how exactly we can know the impedance of an antenna, the complex impedance.....

let say I have a pice of metal , I know the material, I know the antenna size, and the antenna is in the free space, so no other conductor near by...

how can i calculate the complex impedance of the antenna?

thanks

 

[biff44]

Re: Complex Antenna

As you can see, it is a controversial topic!

I would say YES! You can build an antenna like that.

For instance, lets say you had a signle short loop of wide ribbon. It would look inductive, and very low impedance. IF you do not try to match it to 50 ohms, and instead drove it with a current source...then you would have an ultrabroadband antenna that was immune to proximity effects.

To use that same antenna in a receive application, you would hook it to a high impedance voltage amplifier, rather than to a 50 ohm matched LNA.

 

[sh4x]

Re: Complex Antenna

well, I did not mean to discuss a controversial topic, I just curious about it...