Definition of about Gain of antenna

[derndinn]

Could anybody explain what the Gain of antenna means? Increasing Power transmittion?

Ex
1st Antenna have gain 5dBi
2nd Antenna have gain 9dB (Compare with 1st)

For the 1st antenna using both of transmitter and Receiver when power of transmitter is 200 mW . Is the power at receiver 1000mW? if without any loss .

and Is it the same way with 2nd antenna?



Thank you

 

[G4BCH]

Re: About Gain of antenna, Definition.

The first antenna has a gain of 5dB relative to an isotropic radiator. This means that in the direction of maximum radiation the received power will be 5dB higher than if the antenna was an isotropic radiator, ie radiated equally in all directions.
A signal received from the second antenna will be 9dB stronger than the first, or 13dB ( 9+5) stronger than a signal from an isotropic radiator.
There is no power gain as such conservation of energy still holds. The signal has been concentrated into a smaller area rather than radiated everywhere. It is exactly the same as putting a reflector behind a light bulb. The total amount of light being radiated is exactly the same, the light bulb has not changed. The reflector just concentrates what there is in one direction.

 

[derndinn]

Re: About Gain of antenna, Definition.

The signal received or The signal that stronger is not in the form of Power signal ?

 

[jossion]

Re: About Gain of antenna, Definition.

Hi,

didn't understand you question Derndinn...

 

[derndinn]

Re: About Gain of antenna, Definition.

When we receive the signal from transmitter . Received signal is Power signal ? Because i see Pr (dBm) in the friis formula.


Derndinn

 

[G4BCH]

Re: About Gain of antenna, Definition.

The power that you receive from the transmit antenna can be measured in dBm or Watts or what ever units you prefer.
For example assume that the transmit antenna is a dipole and for a given power to that antenna you measure the power output from your receive antenna and it is 0dBm. If you repalce the dipole with antenna 1 the power you will receive will be
0dBm (the power received from the dipole) - 2.1dB (the gain of a dipole relative to an isotropic radiator) + 5dB (the gain of antena 1 relative to an isotropic radiator) i.e you will receive +2.9dBm.
If you replace the transmit antenna with antenna 2 the received signal will increase by 9dB (the gain of antenna 2 relative to antenna 1) i.e 11.9dBm.
These levels only apply at the peak of the main lobe of antenna 1.

 

[vfone]

Re: About Gain of antenna, Definition.

Things are very simple.
Whatever gain the RX and TX antennas have and whatever loss is between them, the received signal power level (at RX input) cannot be higher than transmit power level (at TX output).
In the best case (and ideal) they can be equal.

 

[G4BCH]

Re: About Gain of antenna, Definition.

As I said above
There is no power gain as such, conservation of energy still holds.

 

[derndinn]

Re: About Gain of antenna, Definition.

Thank you for example ^^ , I understood What you said but i am a bit confuse when talking about Power Gain
i attached a paragraph and original link that i read here

'https://ia601608.us.archive.org/28/items/TheArrlAntennaBook/Hall-TheArrlAntennaBook.pdf' Page 43

thank you

 

[derndinn]

Re: About Gain of antenna, Definition.

conservation of energy is not the same as power of signal ?

 

[vfone]

Re: About Gain of antenna, Definition.

https://en.wikipedia.org/wiki/Conservation_of_energy

 

[derndinn]

Re: About Gain of antenna, Definition.

I got it , Thank you so much .