Half wave dipole antenna physics

In summary: VCO at a lower frequency would emit EM at twice the length of the antenna but at a slower rate. The answer is that the antenna only radiates at the frequency of the VCO, but with reduced efficiency if it is not the proper length. The emission rate is always at the speed of light, and the distance an electron travels before its return trip does not directly correspond to the wavelength of the emitted EM. Rather, the electrons just oscillate at the given frequency with a distance that is microscopic. The restriction of the distance by the material does not affect the wavelength of the emitted signal. This thread should not be labeled as advanced when the basics are not yet understood.
  • #1
midz99
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First time poster long time reader.

If i have a half wave dipole antenna with a certain length and I am 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 I am 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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  • #2
midz99 said:
First time poster long time reader.

If i have a half wave dipole antenna with a certain length and I am 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 I am 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.
 
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  • #3
midz99 said:
If i have a half wave dipole antenna with a certain length and I am 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

midz99 said:
example, if i have a half wave dipole antenna measuring 6.25cm and I am 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
 
  • #4
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 doesn't travel far enough how do you still get the same wavelength as the driving frequency?
 
  • #5
midz99 said:
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

midz99 said:
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

midz99 said:
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?

that has already been answered above by tech99 and myself

BTW this thread shouldn't be labelled A for advanced, when you don't even have an understanding of the basics
Dave
 

1. How does a half wave dipole antenna work?

A half wave dipole antenna works by converting electrical energy into electromagnetic radiation. It consists of two conducting elements, each half the length of the wavelength of the signal being transmitted. When an alternating current is applied to the antenna, it creates an oscillating electric field between the two elements, which in turn creates a corresponding magnetic field. These fields interact with each other to form electromagnetic waves that propagate through the air, carrying the signal to the receiver.

2. What is the ideal length for a half wave dipole antenna?

The ideal length for a half wave dipole antenna is equal to half the wavelength of the signal being transmitted. This means that the antenna will be most effective at transmitting and receiving signals at a specific frequency. For example, if the signal frequency is 100 MHz, the ideal length for the antenna would be approximately 1.5 meters.

3. How does the orientation of a half wave dipole antenna affect its performance?

The orientation of a half wave dipole antenna can greatly affect its performance. The antenna works best when it is oriented perpendicular to the direction of the signal. If the antenna is not perpendicular, it can still receive and transmit signals, but there may be a decrease in performance due to a weaker electric field being generated.

4. What factors can affect the range of a half wave dipole antenna?

Several factors can affect the range of a half wave dipole antenna, including the frequency of the signal, the height and orientation of the antenna, and any obstructions or interference in the surrounding environment. In general, a higher frequency will result in a shorter range, while a higher antenna height and clear line of sight will increase the range.

5. Can a half wave dipole antenna be used for both transmitting and receiving signals?

Yes, a half wave dipole antenna can be used for both transmitting and receiving signals. This is because it is a balanced antenna, meaning that the two conducting elements are symmetrical and can be used interchangeably for both functions. However, it is important to properly match the impedance of the antenna to the transmitter or receiver in order to achieve the best performance.

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