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# [SOLVED]Negative gain of antenna

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#### ravindran

##### Newbie level 5
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..

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 ?

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.

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.... ?

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

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.

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

Thanks.

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.

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

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.

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