Why does antenna have a gain?

[netwizio]

why antenna has gain

Is antenna a passive element

if it is
why it possess the gain
as gain is possessed only by the active devices like amplifiers

 

[Borber]

Re: why antenna has gain

Antenna gain is not actually gain as at electronics amplifiers. It is a relative term. Gain is simply quotient of actual antenna received power and isotropic antenna or dipole antenna received power in the same circumstances. When antenna has gain over dipole it will receive more power than dipole. Antenna gain is expressed in dBi or dBd if reference is isotropic or dipole antenna.

 

[unkarc]

Re: why antenna has gain

Hi,

Also, you can see the "gain" as radiating to a specific direction better than in other direction(s). A good example would be if you imagine a parabolic mirror placed behind an incandescent lamp like in an electric torch. The torch can illuminate a certain area in front of it better than for instance the area behind the parabolic mirror.
So an antenna gain is a "passive" one, it has higher amount of radiation to certain direction(s) with respect to other direction(s). The more gain an antenna has in a certain direction the less radiation it has in other directions.

rgds
unkarc

 

[eng_Semi]

Re: why antenna has gain

When an antenna has a gain it means that it isn't an isotropic antenna, it is a directional one, i.e. radiate in a certain direction. So it has a gain which is equal to the directivity * efficency.

Most communication systems use directional antenna rather than omnidirectional one

 

[mohammad mokhtar]

Re: why antenna has gain

Hi
To eleminate confusion ,imagine you have a rod antenna (simplest one) and we connected it to a RF power amp and we choosed a specific point on it at that point if you measure the radiated power for different angles you ll get difeerent reading of RF wattmeter the bigger the reading ,the bigger the gain and each antenna has a polar pattern through which we can measure the gain at different directions,but life is not that simple because we relate it to a reference and that reference is the dipole antenna, and that is what we call antenna gain.it is passive exactly like filament lamp it consumes energy while it radiates light and heat.
Regds

 

[djalli]

Re: why antenna has gain

Is antenna a passive element

if it is
why it possess the gain
as gain is possessed only by the active devices like amplifiers

Usually antenna operates over some frequency. There is no way that metal (or dielectric) is not going to get some inductance or capacitance. Hence these are not passive elements but active elements.

 

[suvendu]

Re: why antenna has gain

yaa,antenna has definitely possesses some gain.because it is aradiating element.operates on radio frequency.in this frequency ,dimension ie wavelength is comparable to size of the conductor hence some capaciative and inductive effect arises .in effect it has some gain.

 

[Borber]

Re: why antenna has gain

Usually antenna operates over some frequency. There is no way that metal (or dielectric) is not going to get some inductance or capacitance. Hence these are not passive elements but active elements.

I do not understand your conclusion. Are you saying that capacitance and inductance are active elements?

 

[awan]

Re: why antenna has gain

hi
the antenna has a specific gain depending upon the aperture size for further information read "wireless communication" by rappaport chap 4 article no 3

 

[userdce]

Re: why antenna has gain

basically what happens to the whole power fed to the antenna gets spread in all the direction if it is omnidirectional antenna. but i this transmitted powr can be cocentrated in a particular direction then that power would definitely be higher than the power transmitted by the omnidirectional antenna in that direction.

so is the gain

it is gain in relative term

as the fundamental law, power can not be created so it is just the cocentration of power from all direction to one particular direction

 

[pran]

why antenna has gain

Directivity of an antenna is defined as the ratio of power radiated/received in a particular direction to that by an isotropic antenna if both are fed by the same input power.

Gain (dB)= 10 log (Directivity* efficiency)

efficency (<=1) is to be included when defining Gain because it takes into consideration the losses of the antenna .

Antenna in the simple sense is a passive device...but active antennas with integrated amplifiers are already emerged.

 

[djalli]

Re: why antenna has gain

Usually antenna operates over some frequency. There is no way that metal (or dielectric) is not going to get some inductance or capacitance. Hence these are not passive elements but active elements.

I do not understand your conclusion. Are you saying that capacitance and inductance are active elements?

Capacitance and inductance are not active elements true, are properties, but devices that exibit capacitance and inductance are active elements which :

1. can have gain
2. can hold change (hence hold memory)
etc.

Yes antennas can have both gain and memory.

 

[power-twq]

Re: why antenna has gain

The gain of antenna is a relative value, not a absolute value

as OP.

best regards

Is antenna a passive element

if it is
why it possess the gain
as gain is possessed only by the active devices like amplifiers

 

[jallem]

Re: why antenna has gain

The main reference antenna, the isotropic one, is the
reference. The isotropic antenna is an antenna which
radiates equally in all directions. So, an antenna which
take some of the energy that is radiating in any direction
and instead put it in other direction will have more energy
radiated in that particular direction and consequently
have a "Gain" with respect the reference(the isotropic).
The antenna does not do anything but "reorient" the energy
so it can concentrate the energy in a particular path.
Any antenna is a passive device even if it has an amplifier.

 

[arrowminds]

Re: why antenna has gain

CAN U EXPLAIN IN SOMPLE WORDS

 

[Eno]

why antenna has gain

antennas are tuned, resonant at certain frequencies.

 

[Nimer]

Re: why antenna has gain

hi

the gain determinse the required and transmitted signal power that in turn determine the distance and the strength of the recieved sugnal .


regards

 

[jinal patel]

why antenna has gain

Antenna is basically passive amplifier. It has higher amount of radiation to certain directions with respect to other directions. The more gain an antenna has in a certain direction the less radiation it has in other directions. so gain descirbe basically directional property of antenny. Also gain of antenna is measured with reference to isotorpic readiater which radiate EM wave in all direction uniformly

 

[PaulHolland]

Re: why antenna has gain

Some are correct other here have to go back to school !. Antenna's have gain because they are able to focus energy in one direction and then it looks like we have gain in that direction. Just like with a spot-light or car lights ! And Antenna's are passive elements just like R, L and C. Active devices need an additional energy source to operate.

 

[cydi]

why antenna has gain

I dont understand the confusion here... It is clear that it only radiates the given energy... So gain is a relative term only!