The total efficiency of an antenna is the ratio of the power radiated from the antenna to the power provided to the antenna at the connector.
The calculator below uses
- Radiation efficiency – ηR
- Voltage Standing Wave Ratio – VSWR
to calculate the Total Antenna Efficiency – ηT.
Both ηR and VSWR can be found in a manufacturer’s data sheet.
Formula
Radiation Efficiency = ηR = PR/PD
Mismatch Efficiency = ηM = 1 – |Γ|2
Γ = (VSWR – 1)/(VSWR + 1)
Total Antenna Efficiency = ηT = ηR * ηM
Total Loss (dB) = 10*Log10(ηT)
Theory
In practical situations, the power radiated by an antenna is less than the power out of the transmitter. Some of the power is reflected back into the transmitter, some of it is absorbed and lost in the antenna itself.
There are three primary sources of loss when using an antenna:
- Mismatch Loss
- Conduction Loss
- Dielectric Loss
Manufacturers will typically only specify the Radiation Efficiency and VSWR as shown in the picture below. We use these two numbers to calculate the total antenna efficiency.
In an ideal situation, VSWR = 1 and ηR = 1. In this case, there are no losses and all the power supplied by the transmitter is radiated. The total losses above can be used in the antenna range calculator. Add the dB value to the cable loss.
Let’s use the numbers from the data sheet above,
- VSWR = 2
- Radiation efficiency = 25% or 0.25 @ 433 MHz.
This gives an Antenna Efficiency of 0.22 and a loss of -6.5 dB.
The performance of the antenna is best at 2450 MHz where the efficiency is 0.8. The loss at this frequency is only -1.5 dB. As a result most of the transmit power will be radiated out of the antenna at this frequency.