Greetings to all of You!
I have searched some research papers for the designing of a proximity coupled patch antenna. Researchers are talking about the impedance bandwidth of the antenna but none of them has given the data about the efficiency of the antenna. Can anyone tell me about the efficiency of the proximity coupled antenna or kindly share any reference paper which will give a better idea about this coupling?
Thanks in Advance.
Your question is not clear. Nonetheless, I can say that there are two types of efficiency: radiation efficiency which depend on the dielectric material. Using lossy dielectric such as FR4 will result in low radiation efficiency (and gain). The mismatch efficiency, however, depends on the coupling/matching between the feed line and the patch. It can be improved by adjusting the spacing/position of the feed line to minimize reflections.
From the feed point of the antenna there are several ways energy can be lost, and they all reduce the efficiency.
There can be a reflection of power if the impedance is not matched. 10 dB reflection coefficient is 1/10 of the power reflected and reduces the efficiency to 90%, for instance. In addition, the transmission line from the feed point to the antenna may lose some power, perhaps 1/2 dB, which is close to 10% lost, so a further 90% multiplier (so 81% efficient so far). The antenna will usually be resonant, so there is the loss resistance of the equivalent resonant circuit which will appear as a current or voltage divider with the (effective) radiation resistance, which might result in 25% of the power being lost in the resonant circuit (patch, wire, loop, matching circuit for small antenna, etc etc etc). This multiplies the efficiency by a further 75%, for example, so it is now about 60% efficient altogether.
The efficiency depends on the type of transmission line, the match, and the type of proximity coupling. If this requires two tuned circuits (the antenna and the coupling circuit), then there will be losses in both. However, by choice of materials and type of resonant circuits and transmission lines, and making sure they are properly matched, proximity coupled antennas should not be much less efficient than any other kind.
Papers often show gain, which is directivity times efficiency. However, they often mean directivity. You can get the efficiency from a 3D gain plot, but only by integrating the gain over the whole sphere and comparing the result to 4pi, which it would be if it was 100% efficient.
The efficiency of an antenna depends upon loss factors like copper loss, radiation loss, dielectric loss, loss due to mismatch, fringing field loss, etc. The frequency of operation, type of material, antenna geometry, feeding techniques, energy coupling techniques, etc. play a significant role in deciding these losses. If we address these issues while designing then the total efficiency of the radiator can be improved.
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