How are smart antennas made?

Antennas are passive devices. According to the angle of the beam, there are two types: omnidirectional antennas and directional antennas. Omnidirectional antennas usually have a large coverage angle, but a short coverage distance. Although directional antennas have a long coverage distance, they sacrifice the coverage angle. So is there an antenna that can cover all angles in all directions and achieve a longer coverage distance at each angle? The answer is yes, that is the smart antenna.

Let's first analyze the shortcomings of omnidirectional antennas and directional antennas in WLAN systems, or the areas that need improvement.

As shown in Figure 1, although the omnidirectional antenna can cover both users in the figure, since the central AP can only exchange messages with one user at each moment, only the blue part forms effective coverage, and most of the other signal propagation causes energy waste, which is invalid coverage. If this part of the wasted energy can be concentrated in the effective coverage area, it is bound to obtain higher signal strength and transmission bandwidth; for directional antennas, due to the concentration of energy, the signal strength in the coverage area will be relatively high, but due to the small signal coverage angle, many areas that need to be covered cannot be reached by the signal. If the signal can be transferred to the user on the left when the user on the right is idle, it is bound to improve the effectiveness of coverage and greatly improve the user's access ability.

Obviously, if the antenna is more "intelligent", when the AP communicates with a user, the antenna will automatically adjust to a directional antenna and aim the "energy beam" directly at the user. On the one hand, the signal strength obtained by the user will be relatively high, and on the other hand, users who should not be "disturbed" will not be disturbed. This result is obviously the most perfect. Smart antennas are born from this.

So from a technical perspective, how can we make smart antennas cover wherever we want at any time according to the needs? There are generally two technical methods: one is beam switching antenna, and the other is adaptive array antenna.

The antenna of the beam switching mode is generally composed of multiple narrow beam antennas. Each narrow beam antenna usually has a large gain and covers a long distance due to its small angle. Generally, when working, for one user, among many antennas, only one narrow beam antenna is in working state. When the user changes or the user's location moves, the smart antenna system will change the working state of the narrow beam antenna according to the situation, that is, stop the previous narrow beam antenna, and then let another narrow beam antenna with the correct angle continue to work. Since narrow beam directional antennas are usually large, such smart antennas are generally used in outdoor scenes. For example, some base stations of TD systems use this smart antenna device, as shown in Figure 2.

The number of antenna angles formed by a beam switching antenna is generally equivalent to that of a narrow beam antenna. Therefore, due to hardware design limitations, this type of antenna cannot have many or very detailed antenna angles to choose from. From the perspective of antenna size, this type of antenna can only be used in outdoor environments, that is, environments where there is not much space requirement.

Adaptive array antenna.

The array antenna is formed by multiple antennas. When working, different antennas work in combination to form different antenna lobes, realizing "virtual antennas" with different directions, angles, and gains to adapt to different working environments, different user locations, and avoid unnecessary interference. When working, the adaptive array antenna can quickly calculate the best antenna combination through the judgment of the working environment and the perception of the user's location, and through internal chip processing, it can achieve the purpose of covering wherever you want. Wireless access equipment can form up to 4096 different lobe patterns through the combination of different antennas, which can easily adapt to various indoor environments, increase coverage, and achieve the purpose of stabilizing network quality.