my dipole antenna has good results. but when i put it on the ARM phantom. its gain becomes negative value (-5.1dB10). I achieve S11, impedance matching.
how we can consider the gain. its ok or not.
in some papers, peoples are also have the negative gain values but they are taking as absolute gain and have read ranges w.r.t gain.
pictures are attached with it.
Q1. how we consider if antenna gain have negative gain?
Q2. Absolute gain relation with gain (db10)?
Negative gain here (dBi) means that the power radiated by test antenna is less than the power radiated by an isotropic antenna in that direction. There are applications in which these can be used, such as where very small range is required.
This isn't surprising. The phantom is a lossy load and is in the near-field of the dipole. It absorbs not only the energy that would be radiated that way, but some of the resonant energy of the dipole. Most antennas will see a reduction in gain when placed on the body, unless they have a ground plane on the body or are quite directional.
The dielectric properties of phantom effects the wave propagation. Although, you can achieve better impedance matching, the gain of antenna within the phantom or near the phantom will be always less than that of free space.
thanks to all
At arm phantom, antenna radiation will be effected. can we use negative gain value as absolute for measuring the read range???
Muhammad Hussain
You do not seem to understand decibels. The negative gain you are seeing is measured in dB which is ten times the log base 10 of a ratio.
0 dB means a ratio of 1.
0 dBi means the same gain as an isotropic lossless antenna, that is what the "i" refers to.
Negative gain in dBi means the gain is less than the gain of an isotropic antenna. Gain of -5 dBi means roughly 1/3 the gain of an isotropic antenna.
Read about decibels and how to use them. If you don't understand decibels you will not be able to understand most antenna and microwave engineering data.
I accept answer of Malcolm White. When tis happens its mens that absolute gain is less tan one. That is possible when in the direction of interest losses are bigger and morrs pronunced than in isotropical direction
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