I have designing microstrip patch antenna and was getting gain and directivity as around 9.5 dB and 8.7 dB approx.But I was getting the value of efficiency in negative.
Can you please clear this confusion.
Thank you.
The antenna efficiency (or radiation efficiency) can be written as the ratio of the radiated power to the input power of the antenna: Er = (P radiated / P input)
is this of any help?
Andy
Gain = Er * Directivity
So efficiency is gain divided by directivity,
therefore 1.09195402299,
and not negative.
As told earlier , gain = efficiency* directivity, you can easily get the efficiency or if you use any software like HFSS or ADS there is a provision that directly plot the efficiency curve and you verify your result..
@Andrew - just a comment. We can't divide two numbers expressed in dB scale (log scale) to find the efficiency. First they need to be converted to absolute scale and then divided. The efficiency 1.09195402299 you suggested was by dividing G and D in dB scale. We can't do that before converting each of them to their absolute values
Alternately,
G = Er * D
or, 10log (G) = 10 log (Er) + 10 log (D)
therefore Er in dB = G in dB - D in dB as rightly pointed out by Russell
Thanks
Dear Anand,
Power gain= Efficiency * Directivity.
For an ideal antenna PG=D, since Efficiency is 1.
In your question you have mentioned Gain as 9.5dBi which must be lesser than Directivity. Due to that reason u may be getting negative efficiency.
Again there are two types of efficiencies. one is radiation efficiency and second one is antenna efficiency.
If gain is larger than directivity it means the efficiency is larger than one. I guess your simulation may not have achieved convergence, there should be some trouble in your simulation.
Negative efficiency means power amplification, unless your antenna is not active it is not physical.
ok then second try, er converted from dB 9.5dB/8.7dB = 8.913/7.413=120.234722784298%
@russell 9.5-8.7 is 0.8dB not -0.8 dB
Kindly see these results in the image.
Gain=5.002 dB
Directivity=7.7670 dBi
And Total Efficiency is coming out to be -9.56 dB.
Efficiency is -2.765
Just convert them into normal values.
You will get efficiency as 52.96%.
But what I am getting according to the simulations is different. So which one is right?
Kindly see the images in my previous answer.
Thank you.
According to gain and directivity values of your images, the efficiency of 52.96 is correct. Even you have not shown efficiency plot.... do you have it, can u show me?
Hi guys,
yes, gain = efficiency*directivity, but efficiency is always between 0 and 1, so of course it is a negative number in dB scale. An efficiency greater than 1 (i.e. more than 100%) or, in other words, greater than 0 in dB scale, has no physical sense for an antenna as it is, because it is a passive component.
@Anand Singh
Be careful: "total efficiency" takes into account also the impedance mismatch at your simulation port, which is different from the radiation efficiency of your antenna.