The impact of antenna efficiency on communication distance
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The purpose of radio frequency is to transmit. When calculating the transmission distance, we usually use the formula to estimate free space transmission:
Lfs (dB)=32.44+20lgd(km)+20lgf(MHz)
Calculate the loss.
If the antenna has gain, the antenna gain DBI will also be calculated.
For example, when transmitting: pout-LFS+dBi is the power value from free space to the receiving end
I work on circuits and don't know much about antennas, so I thought this was a good estimate.
I looked at the data related to antennas these days and found that I had overlooked the transmission efficiency of the antenna.
When talking about antenna efficiency, we have to mention matching and return loss.
When the feed line and antenna are conjugate matched, all the energy is absorbed by the load, and there is only incident wave on the feed line, but no reflected wave.
When the antenna and feeder are not matched, that is, when the antenna input impedance is not equal to the feeder characteristic impedance, the load can only absorb part of the energy.
Return loss RL(dB)=10lg(input power/reflected power)
For example, the picture above
Return loss is 10lg (10/1) = 10dB
The efficiency of an antenna characterizes the energy conversion efficiency of the antenna, that is, the ratio of the antenna's radiated power Pr to the input power Pin, which is called antenna efficiency. Its value is always less than 1.
Part of the energy that is not radiated is reflected back, and part is the loss of the antenna itself. As shown in the figure above, radiation efficiency = 9W/10W*100%=90%.
Return loss is not a commonly used data, the commonly used data are standing wave ratio and reflection coefficient
Return loss RL=-20LG(Г) Г is the reflection coefficient
VSWR = (1 + |Г|) / (1 - |Г|)
Their corresponding table is as follows
The standing wave ratio of commonly used whip antennas can generally be within 2, and the transmission efficiency can reach about 85%.
The standing wave ratio of shortwave antennas for long-distance communications is generally controlled within 1.5, and the transmission efficiency can reach over 90%.
The efficiency of built-in mobile phone antennas is generally around 40%.
With the integration of multiple antennas in the 4G and 5G eras, the efficiency of antennas is further reduced. In order to improve the efficiency, antenna tuning has been introduced to improve the efficiency of antennas.
Summarize
Regardless of the current considerations (limited standards, limited power consumption), the transmission power cannot be increased indefinitely, and the antenna has become the most critical factor in solving the last mile of communication.
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