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How to Calculate Antenna Efficiency, η: Linear (0 to 1), Percentage & dB Explained!
Antenna efficiency is a measure of how effectively an antenna converts the input power into electromagnetic power that radiated out (Transmitter). It is an important parameter for understanding the performance of an antenna.
Definition:
Antenna efficiency (denoted as η) is the ratio of the power radiated by the antenna to the total power input to the antenna. It is expressed as a percentage or as a decimal fraction between 0 and 1.
η = Prad / Pin
Prad is the power radiated by the antenna in the form of electromagnetic waves.
Pin is the total power supplied to the antenna.
Antenna efficiency is also commonly expressed as a percentage. For example, an efficiency of 0.5 is equivalent to 50 %. It is also frequently expressed in decibels (dB); an efficiency of 0.1 corresponds to 10 % or -10 dB, while an efficiency of 0.5 (or 50%) is equivalent to -3 dB.
η distinguishes it from another sometimes-used term, called antenna's "total efficiency". The total efficiency of an antenna is the radiation efficiency multiplied by the impedance mismatch loss of the antenna, when connected to a transmission line or receiver (radio or transmitter).
ηT = η ML
Where ηT is the antenna's total efficiency, ML is the antenna's loss due to impedance mismatch and η is the antenna's radiation efficiency.
A high-efficiency antenna radiates most of the power from its input. In contrast, a low-efficiency antenna loses most of its power, either absorbed as internal losses or reflected away due to impedance mismatch.
Breakdown of Power:
Radiated Power: This is the portion of input power that the antenna successfully converts into electromagnetic waves & radiates into space.
Loss Power: This is the power lost due to various inefficiencies in the antenna, such as:
Ohmic (resistive) losses in the materials that make up the antenna (resistance in the conductors).
Dielectric losses if the antenna is surrounded by a lossy medium.
Impedance mismatch losses when the impedance of the antenna doesn't match the transmission line or source.
The efficiency of an antenna can be affected by factors such as:
Design and materials used: Poor conductors or inappropriate materials can lead to higher losses.
Operating frequency: Antennas may behave differently at different frequencies, affecting efficiency.
Antenna environment: Nearby objects or grounding can introduce losses or distort the radiation pattern.
Importance:
A higher antenna efficiency means more of the input power is effectively used for radiation, which improves overall system performance, especially in communication systems like mobile networks, satellite communication, and radar.
Radiated efficiency measures the ratio of power radiated by the antenna as an electromagnetic wave to the power fed into the antenna terminals. If an antenna were a perfectly ideal electrical component, it would convert all the power fed into its terminals into radiating electromagnetic energy that propagates into the surrounding space. However, this is only theoretical. In practice, some of the power fed into the antenna is always lost. For example, mismatches between the antenna element and the feeding network cause power losses. Additionally, the material of the antenna itself dissipates energy naturally, generating unintended heat. Together, these losses result in antenna radiated efficiency always being less than 100% (equivalent to 0 dB) in real-world conditions. Antenna efficiency is measured in an anechoic chamber by feeding power into the antenna's feed pads and measuring the strength of the radiated electromagnetic field in the surrounding space. Generally, a good antenna radiates 50–60% of the energy fed into it (-3 to -2.2 dB).
Antenna efficiency is a useful and informative measure of an antenna's "economical efficiency." With a quick glance, one can evaluate the antenna's capability to utilize the power fed to the connection pads and determine the amount of power required from the radio module to achieve a certain performance level. Antenna efficiency does not take radiation direction into account, making it a useful performance metric for mobile devices, which typically have an omnidirectional radiation pattern. In mobile devices, no specific radiation direction is emphasized. However, if the antenna is intended to radiate in a specific direction (i.e., the antenna is designed to have directive characteristics in its radiation pattern), then antenna gain is a more appropriate performance metric.
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