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Antenna gain and Directivity.

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Lord Loh.

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Jun 19, 2004
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relation between directivity and gain

What is the difference between the two antenna parameters - Gain and Directivity

Which is practical (not considering the ideal case of isotropic radiators)?

difference between antenna gain and directivity

Directivity of an antenna system towards a given direction(θ,φ) is the radiation intensity normalized by the corresponding isotropic intensity:

Gain of an antenna system towards a given direction(θ,φ) is the total accepted power normalized by the corresponding isotropic intensity:


because Prad=ePt, where e is efficiency factor of antenna we can said:
Gain is directivity multiplicied with efficiency factor of antenna,
G(θ,φ)=eD(θ,φ), 0≤e≤1
look for more about at:

    Lord Loh.

    Points: 2
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the directivity of a half dipole antenna is

gain of antenna is the ratio of input power to the output power of antenna.
while when we are talking about the directionality of antenna it depend upon the radition pattern and bean width of antenna.

difference between directivity and gain

goxy said:
Gain is directivity multiplicied with efficiency factor of antenna,
G(θ,φ)=eD(θ,φ), 0≤e≤1
look for more about at:

Right. Regardless of the common definitions of both Gain and directivity that we all know, I will only add the followings.

Perspective of Efficiency:
First, any system's (antenna+feeder) efficiency is defined as the ratio between the input and the output of such system. You could have an antenna that has high directivity, but, due to losses (conductor losses, dielectric losses, measured by the antenna efficiency or deficiency) your antenna sucks and the overall antenna radiation is not the one desired. That's why we introduce the Gain and Efficiency. The Gain, from the above equation, is defined as the directivity of antenna after being affected by such losses.

Perspective of Direction:
Antenna gain is a parameter which is closely related to the directivity of the antenna. We know that the directivity is how much an antenna concentrates energy in one direction in preference to radiation in other directions. Hence, if the antenna is 100% efficient, then the directivity would be equal to the antenna gain and the antenna would be an isotropic radiator. Since all antennas will radiate more in some direction that in others, therefore the gain is the amount of power that can be achieved in one direction at the expense of the power lost in the others. The gain is always related to the main lobe and is specified in the direction of maximum radiation unless indicated.

difference between gain and directivity

mani_sohail said:
gain of antenna is the ratio of input power to the output power of antenna.
Is an antenna an active element? I know for sure that gain is the increase in power of transmitting in one direction at the cost of reduction in power in another...

Okay m0soles0,

If you are right, my text book is wrong... It id th exact opposite while derriving th eequations and confirms with you in the text part....

gain directivity efficiency

What's exactly the opposite? post some text of your book.
Good luck

efficiency gain directivity

looks like I made a lot of typo errors... :(

I have got no scanner.... But the book is called "Electronic Communications" by Dennis Roody and Coolen.

relation between gain and directivity

OK lets just discuss the similarities and the opposition. Since the book agrees with the text part, it has to be agreed in the equation derivations. Second thing, the book u mentioned is not specialized in antenna theory, u dont have to count on it. Do the search for antenna theory and design for C. Balannis.

Good luck

difference is gain and directivity

Directivity and Gain
Directivity is the ability of an antenna to focus energy in a particular direction when transmitting or to receive energy better from a particular direction when receiving. The relationship between gain and directivity: Gain = efficiency/Directivity. We see the phenomena of increased directivity when comparing a light bulb to a spotlight. A 100 watt spotlight will provide more light in a particular direction than a 100 watt light bulb, and less light in other directions. We could say the spotlight has more "directivity" than the light bulb. The spotlight is comparable to an antenna with increased directivity. An antenna with increased directivity is hopefully implemented efficiently, is low loss, and therefore exhibits both increased directivity and gain.

Gain is given in reference to a standard antenna. The two most common reference antennas are the isotropic antenna and the resonant half-wave dipole antenna. The isotropic antenna radiates equally well in "all" directions. Real isotropic antennas do not exist, but they provide useful and simple theoretical antenna patterns with which to compare real antennas. An antenna gain of 2 (3 dB) compared to an isotropic antenna would be written as 3 dBi. The resonant half-wave dipole can be a useful standard for comparing to other antennas at one frequency or over a very narrow band of frequencies. To compare the dipole to an antenna over a range of frequencies requires an adjustable dipole or a number of dipoles of different lengths. An antenna gain of 1 (0 dB) compared to a dipole antenna would be written as 0 dBd.

directivity max dipole antenna

In reality

Gain = (η1.η2.η3.....).Directivity
where η is due to any loss of energy as
- dielectric loss
- conducting loss
- radiation inefficiency(antenna radiate mainly reactive fields)
- return loss
- crosspolarization
- etc,etc

antenna radiation efficiency factor

Gain of an antenna is E(Θ,φ)/E(Θ,φ)(max) i.e we are comparing the E field in a particular direction with that of an isotropic antenna.
Directivity is the direction in which a given antenna shows maximum field or power.

difference gain directivity

the ratio of the radiation intensity averaged over all directions. the av. radiation intensity is equal to the total power radiated by the antenna divided by 4pi

the ratio of the intensity in a given directions. to the radiation intensity that would be obtained if the power accepted by the ant were radiated isotropically
"gain doesn't include losses arising from impedance mismatches and polarization mismatches. "

in other word
G(max) = Intensity(max)/[(total input accepted power>>lossless isotropic power)/4pi]

D(max) = Intensity(max)/[(total power radiated by tha antenna)/4pi]

= Intensity(max)/[(total input accepted power x efficiency)/4pi]

= G/efficiency


antenna gain efficiency

u can go through the BOOK KD prasad for ANTENNA.

what is directivity of antenna

I guess BALANIS will give u the answer !!!

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