relationship of receive power of antenna and it gain

antenna received power

Hi everyone,

Can any one explain to me the relationship between receive power of the antenna and it gain. I understand that the more gain that you get from the antenna, the more distance you can communicate. However the gain of the antenna is depend on the radiate power. I don't understand how the receive power of an antenna come in to use. Can you guy explain this concept.

thanks

antenna receive power

An antenna has gain when it focusses the signal.
The more narrow is the beam then the more gain the antenna has.

received power of an antenna

Audioguru said:

An antenna has gain when it focusses the signal.
The more narrow is the beam then the more gain the antenna has.

Click to expand...

Thanks for the reply. But how does the gain related to the receive power of the antenna. What is the relationship between distance of communication and the receive power of the antenna. Are there any equation that specify this relationship.

thanks

power received by antenna

A simple antenna radiates or receives in a sphere shape. Ground under the antenna stops radiation below and most antannas stop radiation above. Then the antenna has director rods in front and a reflector rod or dish at its rear.

A single vertical rod is the standard antenna with a hemishere radiation pattern. A dipole has a gain of almost 2 (+2.5dB) because it concentrates the beam in two directions.

power radiated relationship between 2 antennas

1a2s3d4f said:

Hi everyone,

Can any one explain to me the relationship between receive power of the antenna and it gain. I understand that the more gain that you get from the antenna, the more distance you can communicate. However the gain of the antenna is depend on the radiate power. I don't understand how the receive power of an antenna come in to use. Can you guy explain this concept.

thanks

Click to expand...

Quote: However the gain of the antenna is depend on the radiate power.
That is not true, would you explain why you said so?

increase the power on the antennas

1a2s3d4f said:

Can any one explain to me the relationship between receive power of the antenna and it gain I understand that the more gain that you get from the antenna, the more distance you can communicate.

Click to expand...

There is no direct relationship. Received power depends on few factors:
Power radiated from transmitting antenna (linear dependence)

Distance between transmitter and receiver (complicated relation , for short distances it fall with the pwer of distance but also depends on working frequency )

Height above the ground level for both transmitting and receiving antenna (and falling to 0 above "critical distance" appropriate equation you can find yourself)

Directional characteristic of transmitting and received antennas (antennas gain).

Antennas and input impedances matching.

You can trade for example directional characteristic for emitted power (in stationary, point to point system)

1a2s3d4f said:

However the gain of the antenna is depend on the radiate power.

Click to expand...

It is not true antennas gain is parameter on its own , in no relation with transmitted power (or received power).
Antennas gain (from definition) is the ability of transmitting/receiving antenna to focus electromagnetic valve in/from desired direction.

Good analogy is a tungsten lamp.
Its light goes all around ,
If you add a flat mirror on one side of the bulb the radiation in one direction is 2 times higher. (while there is a complete dark behind the mirror), you can say that the flat mirror is a light antenna with the gain = *2 or 10 log 2 = 3 dB (you can find a table matching ratio with dB).

You can place a bulb in parabolic mirror and you focus the light into more narrow beam. You can use a lens, take the light from bigger surface and concentrate it in small area of light sensitive cell The gain is equal to ratio of lens surface to the sensitive element surface.

Antennas gain is the relation between the light power from omni-directional bulb ,
and the amount of light when using mirrors , lenses and the optical devices.
As you see the Gain does not depend on the light source power.

power gain relation

Thanks for all the reply.

I did learn a lot. Correct me if I am wrong. The path loss is depending on the operated frequency, the distance, and the gain of transmitted/received antenna. (Alpha=-147.6+20log(r)+20log(f)-10log(Gt)-10log(Gr)).

The relationship between transmitted power and receive power is also depend on the path loss. (Pr=Pt/alpha). So when gain of the antenna increase, the alpha will increase, the power input to the antenna will be strong. As a result, the radiated will be in far site will be long distance. It that means the communication link will be in greater distance.

Thanks

received power equal transmitted power gain

1a2s3d4f said:

The path loss is depending on the operated frequency, the distance, and the gain of transmitted/received antenna. (Alpha=-147.6+20log(r)+20log(f)-10log(Gt)-10log(Gr)).

The relationship between transmitted power and receive power is also depend on the path loss. (Pr=Pt/alpha). So when gain of the antenna increase, the alpha will increase, the power input to the antenna will be strong. As a result, the radiated will be in far site will be long distance. It that means the communication link will be in greater distance.

Click to expand...

I think that your imagination of processes that take place between transmitter and receiver antennas is correct.
However the way you describe it is not clear.
I would also advice you to check the "20 log (f)" component, I suspect that it is not that simple (but I am not able to advice you correct one).

relation of power & gain

Actually gain is directional. u can assume it as 4 times pi times (intesity in a given direction(x, y, z axis) over accepted power.

gain = 4*π* U/ accepted power

Accepted power relate with maxell equations. as a summary you may say total amount of radiated electric field