What is the "average gain" of an antenna?

[streamlet]

average gain

Known to all, there are definitions of gain in every antenna book. However, as far as I know, I have not met such a term named "average gain", but I came across it in several documents. I wonder anybody here can help me to clarify this concept -- "average gain". Thx.

 

[donny-skb]

average antenna gain

Known to all, there are definitions of gain in every antenna book. However, as far as I know, I have not met such a term named "average gain", but I came across it in several documents. I wonder anybody here can help me to clarify this concept -- "average gain". Thx.

According to my experiences to measure the antenna gain, the average gain of antenna come from calculating the average data values of several gain measurements

 

[madengr]

antenna average gain

If you take a perfect antenna (eff=100% and Zin=50) and integrate the gain pattern over 4*PI sr you should get 0 dB.

Of course you won't get 0 dB with a real antenna so whats left is the inefficiency and mismatch loss. Maybe that's what the average gain tells you? Just a guess.

 

[streamlet]

average gain

Thx for your replys. But I am afraid I can not agree with you.

To madengr:
First, gain pattern includes no informantion about mismatch between antenna and feeding. Second, if we just take the antenna inefficiency into account an do the calculation you mentioned, there will be a minus "average gain", which is contradictive to what I saw. A more important reason why I cannot accept your explanation is that after the process you mentioned, the "average gain" will lose its meaning as a gain, while just becoming a representative of radiation efficiency!

Any further comment?

 

[Azulykit]

can antenna gain be minus

Gain can be thought of as directivity - all loss (including s11). In this sense the gain does include mismatch information.

"Average gain" is a concept that is often used to describe an omni antenna. There often is a variation in gain as one moves about the pattern, in the xy plane for example. Average gain is an attempt to reduce the variation to a single number. Just how to calculate it is really an agreement between the various parties interested in the particular antenna.

I could offer a number of "definitions" but that would probably just start a debate. What it comes down to is that it is difficult to describe a complicated 3D radiation pattern unambiguously with a single number, particularly when the underlying definitions are not stated.

 

[madengr]

average gain

Thx for your replys. But I am afraid I can not agree with you.

To madengr:
First, gain pattern includes no informantion about mismatch between antenna and feeding. Second, if we just take the antenna inefficiency into account an do the calculation you mentioned, there will be a minus "average gain", which is contradictive to what I saw. A more important reason why I cannot accept your explanation is that after the process you mentioned, the "average gain" will lose its meaning as a gain, while just becoming a representative of radiation efficiency!

Any further comment?

That's the point. My initial thought was that you simulating or measuring one of those miniature antenna loaded with high K material? The manufacturer often quotes 0 dB gain for a small patch or inverted F, when the directivity could be 3 dB or higher. They are not to say the their antenna is 50% efficient, but they will say (in small text) that the average gain is -3 dB. It's marketing lingo. It makes their antenna specs looks better, and give you a quick number as to how much power you are radiating.

When I take a measurement in my chamber I do substitution measurement: measure the response of two calibrated reference antennas (horns or dipoles), substitute in my antenna, compute the difference, then subtract that from the published reference antenna gain. This gives me an absolute gain measurement which includes mismatch and efficiency losses (assuming the reference antenna is well matched, which it usually is). Also the formal definition of gain is Gain=eff*Directivity, so gain does include inefficiency, and mismatch loss is rolled into that but it's generally assumed you have matched your antenna.