The efficiency of an antenna refers to the ability of the antenna to convert input electrical energy into radiated energy. In wireless communications, antenna efficiency has an important impact on signal transmission quality and power consumption.
The efficiency of the antenna can be expressed by the following formula:Efficiency = (Radiated power / Input power) * 100%
Among them, Radiated power is the electromagnetic energy radiated by the antenna, and Input power is the electrical energy input to the antenna.
The efficiency of an antenna is affected by many factors, including antenna design, material, size, operating frequency, etc. Generally speaking, the higher the efficiency of the antenna, the more effectively it can convert the input electrical energy into radiated energy, thereby improving the quality of signal transmission and reducing power consumption.
Therefore, efficiency is an important consideration when designing and selecting antennas, especially in applications that require long-distance transmission or have strict requirements on power consumption.
1. Antenna efficiency
Figure 1
The concept of antenna efficiency can be defined using Figure 1.
The total antenna efficiency e0 is used to calculate the antenna losses at the input and within the antenna structure. Referring to Figure 1(b), these losses may be due to:
1. Reflections due to mismatch between the transmission line and the antenna;
2. Conductor and dielectric losses.The total antenna efficiency can be obtained from the following formula:
That is, total efficiency = product of mismatch efficiency, conductor efficiency and dielectric efficiency.It is usually very difficult to calculate conductor efficiency and dielectric efficiency, but they can be determined by experiments. However, experiments cannot distinguish the two losses, so the above formula can be rewritten as:
ecd is the radiation efficiency of the antenna and Γ is the reflection coefficient.
2. Gain and Realized Gain
Another useful metric for describing antenna performance is gain. Although the gain of an antenna is closely related to directivity, it is a parameter that takes into account both the efficiency and directivity of the antenna. Directivity is a parameter that only describes the directional characteristics of an antenna, so it is determined only by the radiation pattern.The gain of an antenna in a specified direction is defined as “4π times the ratio of the radiation intensity in that direction to the total input power.” When no direction is specified, the gain in the direction of maximum radiation is generally taken. Therefore, there is generally:
In general, it refers to relative gain, which is defined as “the ratio of the power gain in a specified direction to the power of a reference antenna in a reference direction”. The input power to this antenna must be equal. The reference antenna can be a vibrator, horn or other antenna. In most cases, a non-directional point source is used as the reference antenna. Therefore:
The relationship between total radiated power and total input power is as follows:
According to the IEEE standard, “Gain does not include losses due to impedance mismatch (reflection loss) and polarization mismatch (loss).” There are two gain concepts, one is called gain (G) and the other is called achievable gain (Gre), which takes into account reflection/mismatch losses.
The relationship between gain and directivity is:
If the antenna is perfectly matched to the transmission line, that is, the antenna input impedance Zin is equal to the characteristic impedance Zc of the line (|Γ| = 0), then the gain and the achievable gain are equal (Gre = G).
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