# Half wave dipole antenna physics

• B
First time poster long time reader.

If i have a half wave dipole antenna with a certain length and im using a VCO to drive that antenna at lower driving frequency do i get EM at the length of twice the length of the antenna but just at a slower emission rate?

example, if i have a half wave dipole antenna measuring 6.25cm and im using a VCO to drive that antenna at only 1ghz where i should be using 2.4ghz, will that antenna still emit EM at 2.4ghz but at a rate of 1ghz?

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tech99
Gold Member
First time poster long time reader.

If i have a half wave dipole antenna with a certain length and im using a VCO to drive that antenna at lower driving frequency do i get EM at the length of twice the length of the antenna but just at a slower emission rate?

example, if i have a half wave dipole antenna measuring 6.25cm and im using a VCO to drive that antenna at only 1ghz where i should be using 2.4ghz, will that antenna still emit EM at 2.4ghz but at a rate of 1ghz?
The antenna only radiates the frequency of the VCO. If it is of the "wrong" length, then efficiency is reduced, but frequency is unaltered.

berkeman and midz99
davenn
Gold Member
2019 Award
If i have a half wave dipole antenna with a certain length and im using a VCO to drive that antenna at lower driving frequency do i get EM at the length of twice the length of the antenna but just at a slower emission rate?
The EM wave is always radiated/emitted at the speed of light

example, if i have a half wave dipole antenna measuring 6.25cm and im using a VCO to drive that antenna at only 1ghz where i should be using 2.4ghz, will that antenna still emit EM at 2.4ghz but at a rate of 1ghz?
As tech99 said the emission will be poor
This is because the antenna isn't resonant for the 1 GHz frequency from the VCO

i think you miss understand what i meant by emission rate, each cycle back and forward of electron movement creates EM, now if the driving frequency was 2GHz then emission rate would be 2GHz. The distance an electron travels before its return trip directly corresponds to the wavelength of EM you get. but if that distance is restricted by length of the material, so it doesnt travel far enough how do you still get the same wavelength as the driving frequency?

davenn
Gold Member
2019 Award
now if the driving frequency was 2GHz then emission rate would be 2GHz.
forget about the term emission rate ... isn't a term used for RF and antennas .... use frequency
The RF signal is emitted at the speed of light regardless of its frequency

The distance an electron travels before its return trip directly corresponds to the wavelength of EM you get
no, the electrons just oscillate about a point at the given frequency. The distance they move at 2GHz is nigh microscopic in length

but if that distance is restricted by length of the material, so it doesn't travel far enough how do you still get the same wavelength as the driving frequency?