Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

What is the unit for antenna gain?

Status
Not open for further replies.

saran7507

Member level 3
Joined
Nov 14, 2008
Messages
57
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,788
antenna gain

Hi All,

Can anybody tell me what is the unit for the antenna gain? We are using friis equation to get the gain value ....what would be the unit called ?

dBi or dBd.............


Waiting for your reply.


Thanx.

Regards,
Saran
 

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,955
Helped
1,369
Reputation
2,734
Reaction score
1,045
Trophy points
1,393
Location
New England, USA
Activity points
37,223
antenna voltage gain

Because dBi is slightly larger number, data sheets almost always use dBi. dBi is simply dBd + 2.1 dB.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,858
Helped
1,746
Reputation
3,496
Reaction score
1,346
Trophy points
1,393
Location
Germany
Activity points
39,554
isotropic antenna gain

biff44 said:
Because dBi is slightly larger number, data sheets almost always use dBi. dBi is simply dBd + 2.1 dB.

That´s OK.
However, perhaps somebody is interested in the meaning of this abbreviation "dBi".
Background: dB corresponds to a simple number. As an antenna does not amplify a signal it does not multiply it with a number (as an amplifier does). Therefore the unit cannot be "dB".
But a directional antenna forms a beam and concentrates the power into one direction - leading to a gain figure if compared with the (theoretical case of an) isotropic antenna. Thus, it has x dB more power in that direction than for the isotropic case. That´s the meaning of "dBi".
 

mauloftin

Full Member level 6
Joined
Oct 29, 2008
Messages
357
Helped
62
Reputation
122
Reaction score
36
Trophy points
1,308
Location
CZ
Activity points
3,285
how does dbi work antenna gain

LvW said:
biff44 said:
Because dBi is slightly larger number, data sheets almost always use dBi. dBi is simply dBd + 2.1 dB.

That´s OK.
However, perhaps somebody is interested in the meaning of this abbreviation "dBi".
Background: dB corresponds to a simple number. As an antenna does not amplify a signal it does not multiply it with a number (as an amplifier does). Therefore the unit cannot be "dB".
But a directional antenna forms a beam and concentrates the power into one direction - leading to a gain figure if compared with the (theoretical case of an) isotropic antenna. Thus, it has x dB more power in that direction than for the isotropic case. That´s the meaning of "dBi".

I think:

"dBi" compared radiation intesity with isotropic antenna and "dB" compared rad. intensity with antenna input power. But it's the same number of course
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,858
Helped
1,746
Reputation
3,496
Reaction score
1,346
Trophy points
1,393
Location
Germany
Activity points
39,554
antenna gain unit

Quote mauloftin:
I think:
.............. and "dB" compared rad. intensity with antenna input power. But it's the same number of course


No, that´s definitely not correct.
You cannot radiate more power than available at the antenna input.
 

mauloftin

Full Member level 6
Joined
Oct 29, 2008
Messages
357
Helped
62
Reputation
122
Reaction score
36
Trophy points
1,308
Location
CZ
Activity points
3,285
antenna gain 10 or 20 db?

LvW said:
No, that´s definitely not correct.
You cannot radiate more power than available at the antenna input.

Of course. the correct is that is norm, exactly:

Gain (IEEE): Norm the plot to the total input power. (Formula from CST MWS)

btw if compared rad. intensity with antenna input power you cannot > 0 dB, of course. The formula is:

G = 4pi(rad.intensity/input power)

so there is constant 4pi (it is from sphere) - so that this number can be > 0 dB
 

Azulykit

Advanced Member level 4
Joined
Feb 18, 2007
Messages
1,135
Helped
220
Reputation
438
Reaction score
113
Trophy points
1,343
Location
All over the Map.
Activity points
8,547
dbi from radiation intensity

Hi Saran,

Antennas are usually compared to a "standard" and described as having a gain some number of dB above or below the standard. The "i" refers to an isotropic antenna while the "d" is referenced to a dipole. You may also encounter other notation as well often indicating a particular polarization of the reference. I see dBi most often in my work.

10 dBi is for example 10 db above an isotropic antenna.

Think of this a little like power or voltage references like dBW, dBm, dBmV and the like.
 

akltt

Newbie level 4
Joined
Apr 17, 2008
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
libya
Activity points
1,318
meaning of dbi antenna

the unit of antnna gain is dBi where the subscript i indicattes the isotropic antenna
 

Meenakshi Sood

Newbie level 5
Joined
Apr 23, 2009
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,328
antenna gain: voltage or power

Gain can be in both terms dBi and dBd
if u r measuring in refrence to istropic antenna(which is the norm) then its dBi

and if refrence with sm directive antenna then dBd

Data sheets show dBi reading
 

alphanov

Newbie level 2
Joined
Jun 7, 2009
Messages
2
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,295
antenna gain units

saran7507 said:
Hi All,

Can anybody tell me what is the unit for the antenna gain? We are using friis equation to get the gain value ....what would be the unit called ?

dBi or dBd.............


Waiting for your reply.


Thanx.

Regards,
Saran
An isotropic radiator at the centre of a sphere will illuminate the surface of the sphere equally in all directions. If that radiator is replaced by, say, a dipole antenna then the surface of the sphere will not be illumnated evenly. Since the energy, assuming the same transmitted power, is distributed differntly in both cases then the dipole will have an apparent gain over the isotropic. This, numerically, is a gain of 1.64 or 2.16dBi. Some antenna manufacturers then reference their product against the radiation achieved from a dipole and then express this as a gain in dBd. A dipole has 0dBd gain. Hope this makes sense!
 

mounika

Newbie level 5
Joined
Jun 23, 2009
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
hyderabad
Activity points
1,312
0 db isotropic antenna gain

hi,
can anyone tell me what is the gain of antenna
 

DaveN

Junior Member level 2
Joined
Apr 17, 2009
Messages
23
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,281
Location
Sydney, Australia
Activity points
1,488
what is the gain value of isotropic antenna?

As some one has already said...
dBi is referencing the gain to an isotropic radiator

BUT
dBd is referencing the gain to a dipole radiator

NOTE >>>> ( AT THE FREQUENCY OF INTEREST)

Therefore, any antenna gain should be referenced to one of those 2
they are the 2 standards used
to just say that an antenna has a 20 dB gain is totally meaningless
... 20dB gain over what ???? a wet piece of string ?? my mouse cable ???
my granny's wooden leg???
it has to be referenced to something
if you see an antenna for sale/quoted (etc) without a dBd or dBi reference
ASK the dealer/user to clarify, if he cant, he shouldnt be working with
antennae ;)

Quote...but all antenna have in description "gain is x dB" - only dB, no dBi or dBd. So, can you tell me if is dB = dBi or dB = dBd (for antennas) ? Unquote

As I have already stated that is NOT correct it MUST have a reference dB DOES NOT = dBd ot dBi

dB ... is just a ratio measurement of power, voltage, whatever of output voltage etc Verses input voltage or watever what ever

eg .. you can say that an amplifier audio or RF has a gain 20 dB

10 log (P2/P1) dB where the log is to base 10. where P1 = input P2 = output

and to move away from antennae with dBd or dBi

you can move to power levels with the common references of
dBm (reference 0dBm = 1mW) or dBW (reference 0dBW = 1W)

cheers
Dave
VK2TDN
DC - DAYLIGHT

Added after 40 minutes:

mounika said:
hi,
can anyone tell me what is the gain of antenna

what sort of antenna operating on what freq ?
is it a yagi ? how many elements
is it a dish antenna ? what diameter ?

you have to be specific?

Dave
DC to Daylight
 

engr_najam

Full Member level 2
Joined
Aug 10, 2006
Messages
129
Helped
7
Reputation
14
Reaction score
1
Trophy points
1,298
Activity points
1,939
radiator antenna gains

I am not sure, but if it is gain than it is the ratio of two same quantities, which means their units cancel out, hence no unit.
dB means the ratio is logarithmic form multiplied by 10 for power or 20 for voltage.
 

DaveN

Junior Member level 2
Joined
Apr 17, 2009
Messages
23
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,281
Location
Sydney, Australia
Activity points
1,488
what are the units for antenna gain

engr_najam said:
I am not sure, but if it is gain than it is the ratio of two same quantities, which means their units cancel out, hence no unit.
dB means the ratio is logarithmic form multiplied by 10 for power or 20 for voltage.

YES for an amplifier that is correct, it is just dB. BUT as already said, for an antenna the gain MUST always be
referenced to something... and that something is ALWAYS to the 2 most basic antennae ... either a isotropic radiator
= dBi or to a dipole which is dBd

that is because you are NOT comparing input power/voltage to output power/voltage to get a plain dB gain...
instead you are comparing the gain of a given antenna, say a 5 element yagi, over a "standard radiator"
and comparing how much better (hopefully) that the yagi performs over a known standard antenna

cheers
Dave
VK2TDN
 

Aya2002

Advanced Member level 4
Joined
Dec 12, 2006
Messages
1,142
Helped
184
Reputation
376
Reaction score
118
Trophy points
1,343
Location
Iraq
Activity points
8,006
relation between dbi&dbm

is there a relationship between dB, dBi, and dBm?
thanks
 

DaveN

Junior Member level 2
Joined
Apr 17, 2009
Messages
23
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,281
Location
Sydney, Australia
Activity points
1,488
working out antenna gains

Aya2002 said:
is there a relationship between dB, dBi, and dBm?
thanks

only in that they use the logrithmic scale of dB (deciBel) to measure loss or gain
power = Log 10, Voltage = Log 20

dB = could be a power or voltage gain or loss (loss if -dB (negative dB))

dBi = for antenna

dBm = is as I related a few reply's ago, purely a Power measurement....
my quote...
you can move to power levels with the common references of
dBm (reference 0dBm = 1mW) or dBW (reference 0dBW = 1W)

In RF work we like to work in dBm or dBW (in my case dBm) as I am generally working with power levels
less than 100 Watts. Using dBm for all calculations simplifies working out losses amd gains in a RF system eg

transmitter pwr out - cable loss + Antenna Gain - pathloss + Receiver ant. gain - receive cable loss + receiver gain
insert some examle figures....

30dBm (1W) - 3dB (cab Loss) + 35dBd (ant gain) - 150dB (pathloss) +35dBd (RX ant gain) - 4dB(RX cab loss) + 40dB RX gain

its much easier and practical to use every thing in dB rather than mixing actual power levels eg Watts or milliWatts
with other system gains and losses measured in dB

Also dont forget, the dB = deciBel = 1/10 (1 tenth of a Bel) is also a measure of sound level

Dave
VK2TDN
 

Aya2002

Advanced Member level 4
Joined
Dec 12, 2006
Messages
1,142
Helped
184
Reputation
376
Reaction score
118
Trophy points
1,343
Location
Iraq
Activity points
8,006
unit for gain in antenna

thanks friend
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top