[SOLVED] Negative gain of antenna

[ravindran]

Our project deals with miniaturization of patch antenna. We were successful in reducing the resonant frequency from 5 GHz to 2.41 GHz by simulation using HFSS. But the gain of the antenna we obtained after miniaturization was -1.7 dB. We are confused with this. Is there any problem if the antenna gain is negative. (the gain before miniaturization was 6.9db). please help..

 

[Ow@i$]

Before Posting any query always first search the forum for your answer, surely you will find something worth reading!

anyways have a look!!

https://www.edaboard.com/threads/122653/
https://www.edaboard.com/threads/251706/
https://www.edaboard.com/threads/237763/

 

[kripacharya]

any gain (+ve dB or -ve dB), since it is measured in dB, is the log of the ratio of two numbers.

So the question to ask is - what is your reference number ? And for an antenna i would usually assume an ideal isotropic antenna power. But what is it in your case ?

 

[ravindran]

I am talking about my simulation result. The main aim of my project is miniaturization and i am not that concerned about my gain, but is -1.5 db too low for an antenna? As i am doing the simulations in hfss i think the gain is shown with respect to an isotropic radiator.

 

[kripacharya]

I am talking about my simulation result. The main aim of my project is miniaturization and i am not that concerned about my gain, but is -1.5 db too low for an antenna? As i am doing the simulations in hfss i think the gain is shown with respect to an isotropic radiator.

only you yourself can answer this question. a negative dB gain implies less-than gain from ideal isotropic. Whether it is enough for your purpose..... well.... ?

 

[Ow@i$]

There are antenna which on purpose are designed with negative gain... so in the end it all goes what and how much you want !!

 

[drkirkby]

As someone else stated, you need to state the reference. Since you are using HFSS, by default that wil give you dBi, so we can assume the gain is -1.7 dBi. Since any antenna will radiate more strongly in one direction than another, a lossless antenna must have a gain greater than 0 dBi. However, if the antenna is not lossless, then the gain will reduce, and a gain less than that of an isotropic radiator is quite possible.

 

[safaluna]

Hello,
I am the same problem I get a negative gain along the frequency band . Can you help me please???

Thanks.

 

[biff44]

Another thing to consider is simply the size. Antennas want to be a certain minimum size to work efficiently at one frequency. Lets say you get an antenna to "work" at a lower frequency than you would expect it to. You typically give up some gain (or efficiency, etc) to do so. You can research this in a number of papers on "electrically small antennas" or "radiation resistance". For various reasons, even if you can get a good impedance match, the microwave energy is absorbed resistively in the antenna itself (or possibly the nearby surroundings--ground plane) and not fully radiated.

 

[kripacharya]

Hello,
I am the same problem I get a negative gain along the frequency band . Can you help me please???

Thanks.

what - exactly - is your concern ? Negative gain simply means that your gain is less than that of an isotropic antenna

 

[Azulykit]

Negative gain occurs when the internal and reflection losses are greater than the directivity of your particular antenna. It can also occur if your simulation is FUBAR because of a modeling error or software bug.

Electrically small antennas often have disappointing gain numbers e. g. negative. Everyone wants small antennas but usually they hate the performance.