how to get gain from directivity ?

[waqas jaan]

Dear All.

i have designed an antenna with directivity of 6.907dBi. what will the value of gain here ? i mean how to get gain from this respective directivity ?
while the radiation efficiency of such antenna is -2.056dB.

 

[Vengateswaran]

whether the directivity you have calculated is maximum directivity..?? if so, u can get maximum gain as, G=radiation efficiency * Directivity... But for your calculation, u'll be getting negative gain...

 

[waqas jaan]

thank you for your support.

yes it is the maximum directivity.
but as you mentioned, that G = rad eff * dir. so whether shall i multiply it in the value of dB or to convert it from dB and than multiply it ?

 

[albbg]

You have to operate in linear, that is convert dB to lin, multiply and then convert back, the result, to dB.

G=10^(6.907/10)*10^(-2.056/10) = 3.056 lin
G(dBi) = 10*log(3.056) = 4.85 dBi

 

[waqas jaan]

Thank you so much, i got it.

what do you think ? is it good or not ? i mean 4.85dBi or 6.40dBi is a good gain or not ?

 

[Vengateswaran]

I don't think it is good... it can be used for low end applications..

 

[waqas jaan]

actually it is microstrip patch antenna at resonant freq of 5.2GHz.

 

[Vengateswaran]

I think it is partially less when looking at your design... But i dont know exactly...

 

[albbg]

If that directivity you wanted to achive is OK (this means the angle over which the power is radiated, mainly) then is only matter of efficiency.
You reached -2.056dB, that is 62%. Usually patch antennas have efficiency ranging rouglhly from 50 to 90% then you are inside it. This depends from factors like substrate losses, material conductivity, etc.

However if you could increase the efficiency up to the ideal 100 % the gain will increase 10*log10(100/62)=2 dB; not so much.