Electronics > Beginners
Why do we need antennas?
Damianos:
The question is: Why do we need antennas?
Some similar questions may be:
Why do we need microphones and speakers?
Why do we need light bulbs?
Why do we need electric fans?
... electric water pumps?
... ...
All the above are transducers/converters between electricity and something else!
Similarly an antenna is converting electricity to radio waves and vise versa. It is a radiator and receptor of radio waves.
The simplest form of it is the dipole...
The transmission line is another story... We need it when we have to transfer the RF power from one place to another. If we connect our antenna directly to our generator, we don't need it...
bsfeechannel:
--- Quote from: Damianos on August 16, 2018, 06:36:16 pm ---All the above are transducers/converters between electricity and something else!
Similarly an antenna is converting electricity to radio waves and vise versa. It is a radiator and receptor of radio waves.
The simplest form of it is the dipole...
The transmission line is another story... We need it when we have to transfer the RF power from one place to another. If we connect our antenna directly to our generator, we don't need it...
--- End quote ---
Antennas are not transducers not transformers. The principles that govern antennas are the same for transmission lines.
What antennas and transmission lines basically do is to shape the boundary conditions for the propagation of electromagnetic waves.
These conditions are cleverly chosen to make the waves behave as intended.
fonograph:
--- Quote from: tautech on August 15, 2018, 09:34:51 pm ---
--- Quote from: fonograph on August 15, 2018, 09:28:33 pm ---If wave impedance and electric impedance are not related.Can you two antennas,one low electric impedance high current,second high electric impedance high voltage one and if their wave impedance is same and they are both fed samw amount of power,then they will radiate the same?
--- End quote ---
No.
Poor SWR will rob the high impedance version of performance.
--- End quote ---
Why would there be SWR problem?
fonograph:
--- Quote from: IanB on August 15, 2018, 09:36:35 pm ---
--- Quote from: fonograph on August 15, 2018, 09:28:33 pm ---If wave impedance and electric impedance are not related.Can you two antennas,one low electric impedance high current,second high electric impedance high voltage one and if their wave impedance is same and they are both fed samw amount of power,then they will radiate the same?
--- End quote ---
Think about electricity. You can transmit the same amount of power using high voltage and low current (requiring thinner cables), or using lower voltage and higher current (requiring thicker cables).
With electromagnetic radiation something similar happens with frequency. At higher frequencies and shorter wavelengths photons have more energy, so you can transmit a certain amount of power using smaller antennas. At lower frequencies and longer wavelengths photons have less energy, so you need bigger antennas to transmit the same amount of power.
Once again, size comes into it.
--- End quote ---
While I am thankful for your informative post it was information completly unrelated to my question.At no point did I mention antenna size.I know lower frequencies need bigger antenna,my question was about antenna electric impedance.
fonograph:
--- Quote from: PhilipPeake on August 15, 2018, 06:55:12 pm ---But they are related.
--- End quote ---
How are they related? First success of this thread was informing me there are two kinds of impedances,electric and wave.Now you claim they arent indepedent and unrelated as I expected,then in what way are they related? Correct me if I am wrong,but you want to have 377 ohm wave impedance antenna so it can theoretically radiate 100% energy.
Can this 377 ohm wave impedance be achieved no matter what electric impedance the antenna have? Can there be high electric impedance antennas like 1 M ohm,high voltage and still have 377 ohm wave impedance and as result be efficient?
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