Since light is an electromagnetic wave, is it possible to build an antenna to receive many different frequencies? From KHz to THz? Or the wavelength makes it impossible?
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$\begingroup$ This does not need to be done specially, because each antenna receives the full spectrum. The main engineering problem is how to amplify the signal of the desired frequency. $\endgroup$– user13964273Commented Nov 24 at 12:58
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$\begingroup$ @user13964273 An antenna designer has two main problems of when the operating frequencies are: (1) to match the antenna impedance to that of the receiver and/or transmitter meanwhile (2) the antenna is to have the desired radiation pattern. "Amplification" is not a meaningful concept for antennas and is never a specified parameter; what is called "antenna gain" is not an "amplification". $\endgroup$– hyportnexCommented Nov 24 at 21:51
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$\begingroup$ All antennas receive/transmit all frequencies, what distinguishes them is the efficiency with which those frequencies are received/transmitted. $\endgroup$– hyportnexCommented Nov 24 at 21:55
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1 Answer
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The problem with a transmitting antenna is that the electrons, accelerated back and forth on the antenna rod, build up a counter-potential to the wave generator at the rod ends. For long-wave transmitters where you don't want to build higher than 100+ meters, pots are placed at the antenna end.
An incredibly small portion of the emitted photons arrives at the receiving antenna. These photons are polarized and their field component - usually the electric one - causes the movement of electrons in the receiving metal. Today's electronics are truly a marvel, detecting the periodic signal of the carrier frequency from the noise of the incoming radiation and then recognizing the imprinted information.
light is an electromagnetic wave
Radio waves are an EM wave. The synchronous and periodic acceleration of surface electrons in the transmission rod causes the periodic emission of polarized photons. In very clear terms, we are dealing with a periodicity in the number of photons leaving the antenna.
All EM radiation from thermal sources shows an intensity distribution behind slits - from which Young deduced their wave character - but you only get a thermal source as an information carrier if you switch this source on and off or, better still, if you periodically change the intensity of the thermal source and modulate a signal onto it. If you use a laser, an LED or an electric light bulb for this, then you have recreated an antenna in the visible range.
is it possible to build an antenna to receive many different frequencies?
The only limitations you have in turning any piece of metal into a receiving antenna are the size of the incident area to capture enough photons, the mobility of the electrons to the evaluation electronics and the sensitivity of the electronics to filter out a transmitting source and then extract the modulated information.
answered Nov 26 at 4:43
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$\begingroup$ This could also be interesting Can a microwave antenna detect single microwave photons? $\endgroup$ Commented Nov 26 at 4:45