How to convert dB to dBi value?

please help me because i got confused between dB and dBi

im designing an antenna for my undergrand final year project

using HFSS i got the Gain without unit ( 0.665) relative then i have conveted it to dB using this eq

10log0.655

and i got -1.837dB after that how i can convert it to dBi and do i have to consider the negative sign or i should ignore it


thanks in advance for helping me ;)

dB is a relative measurement between two power levels. It is not tied to any particular reference.

dBi on the other hand is a comparison between a measurement and an omni-directional antenna (hence the small i attached to dB). An omni directional antenna radiates in all directions equally (no internal loss). Positive gain numbers indicate greater than omni and lower numbers indicate less than omni response in that particular direction.

A dipole for example has about 2.1 dBi gain (max) and has a toroidal pattern that is reasonably close to an omni.

It is not clear to me what you were doing with the post processor in HFSS. First work on understanding the basic ideas and then try to figure out what you were doing with the software.

ok thanks for your explanation but still i have some confusion

i attached a file please try to see the result i got for micro strip patch antenna

peak gain = 0.66351

there no any indicating unit

so which unit i should consider for it and how i can put it in dB or dBi


your cooperation is highly appreciated

what is dBic?

dBic is referenced to a circularly polarized isotrope. I have never seen a distinction between RHCP and LHCP omni's but it could be an issue.

This has a potential to get very convoluted if care is not taken to make sure all the players are on the same page.

I would recommend a conversation with Ansoft about the details of their code. Their application engineers are worldwide and very helpful.