AGI (Antenna Gain Imbalance)

Last updated on Feb 24, 2023

Antenna Gain Imbalance (AGI) is a phenomenon that can occur in communication systems that use multiple antennas to transmit and receive signals. In this situation, the gain of the different antennas may not be equal, leading to a difference in the amount of power transmitted or received by each antenna. This can cause significant problems for the overall performance of the communication system, as it may result in degraded signal quality, reduced range, and increased interference.

In this article, we will discuss the concept of antenna gain imbalance in detail. We will look at how it arises, how it can be measured and corrected, and its impact on communication systems. We will also explore some of the techniques used to mitigate antenna gain imbalance and ensure optimal performance of communication systems.

What is Antenna Gain Imbalance?

Antenna gain is a measure of the ability of an antenna to transmit or receive signals in a particular direction. The gain of an antenna is expressed in decibels (dB) and is a ratio of the power density radiated or received by the antenna in a given direction compared to an isotropic radiator (a hypothetical antenna that radiates equally in all directions).

In a communication system that uses multiple antennas, it is essential that the gain of each antenna is equal. If there is a difference in gain between the antennas, it can result in a phenomenon known as antenna gain imbalance (AGI). AGI occurs when one or more antennas in a communication system have a higher or lower gain than the others.

In a multiple-antenna system, such as a MIMO (Multiple Input Multiple Output) system, AGI can cause the transmitted signal to be distorted or attenuated, leading to a reduction in the signal quality. Similarly, in a receive-only system, AGI can cause some antennas to receive a stronger signal than others, leading to an unbalanced received signal and a degradation of the overall system performance.

Measuring Antenna Gain Imbalance

Antenna gain imbalance can be measured in several ways. One method is to use a specialized test set that is designed to measure the gain of each antenna in a multiple-antenna system. The test set transmits a signal from each antenna and measures the power received by each of the other antennas. The gain of each antenna is then calculated by comparing the transmitted and received powers.

Another method for measuring AGI is to use a channel sounding technique. In this approach, a known signal is transmitted from each antenna in turn, and the received signal is measured. By comparing the received signal strength from each antenna, the AGI can be calculated.

Correcting Antenna Gain Imbalance

There are several techniques that can be used to correct antenna gain imbalance. One common approach is to adjust the gain of the antennas to ensure that they are equal. This can be done manually by adjusting the antenna hardware or electronically by adjusting the signal levels.

In some cases, it may not be possible to adjust the gain of the antennas, or it may not be desirable to do so. In these situations, it is possible to use signal processing techniques to mitigate the effects of AGI. One approach is to use beamforming, which involves adjusting the phase and amplitude of the signals transmitted from each antenna to produce a coherent beam in the desired direction. This can help to reduce the impact of AGI on the overall system performance.

Another approach is to use equalization techniques, such as Maximum Ratio Combining (MRC), which combine the received signals from each antenna to produce a single, more accurate signal. MRC is based on the principle of weighting the received signals from each antenna by their respective gains to maximize the overall received signal-to-noise ratio.

Impact of Antenna Gain Imbalance on Communication Systems

Antenna gain imbalance can have a significant impact on the performance of communication systems, especially in situations where the signal-to-noise ratio (SNR) is already low. In a MIMO system, AGI can cause the transmitted signal to be distorted, leading to a reduction in the signal quality. This can result in errors in the received data, reduced data rates, and increased interference. In addition, AGI can also cause the system to become less robust to interference, which can further degrade the overall system performance.

In a receive-only system, AGI can cause some antennas to receive a stronger signal than others, leading to an unbalanced received signal and a degradation of the overall system performance. This can result in errors in the received data, reduced data rates, and increased interference.

Mitigating Antenna Gain Imbalance

There are several techniques that can be used to mitigate the effects of AGI on communication systems. One approach is to use beamforming, which involves adjusting the phase and amplitude of the signals transmitted from each antenna to produce a coherent beam in the desired direction. This can help to reduce the impact of AGI on the overall system performance.

Another technique that can be used to mitigate the effects of AGI is to use antenna calibration. This involves measuring the gain of each antenna in the system and adjusting it to ensure that they are equal. Calibration can be done manually by adjusting the hardware of the antenna or electronically by adjusting the signal levels.

Conclusion

Antenna Gain Imbalance (AGI) is a common problem that can occur in communication systems that use multiple antennas. AGI occurs when one or more antennas in a communication system have a higher or lower gain than the others. AGI can cause the transmitted signal to be distorted or attenuated, leading to a reduction in the signal quality. Similarly, in a receive-only system, AGI can cause some antennas to receive a stronger signal than others, leading to an unbalanced received signal and a degradation of the overall system performance.

There are several techniques that can be used to mitigate the effects of AGI on communication systems, including beamforming, equalization techniques, and antenna calibration. By using these techniques, it is possible to ensure optimal performance of communication systems, even in situations where AGI is present.