Many users, when choosing a new router or noticing unstable wireless network performance, pay attention to the number and placement of antennas on the device. This naturally raises the question: why do some routers have two permanently fixed antennas, while others have three or four removable, rotatable antennas? The answer lies in the physics of radio wave propagation and a technology known as antenna diversityThis isn't just a marketing ploy to give the device an "aggressive" appearance, but a necessary engineering technique to ensure a stable connection.
The essence of the method is that the use of multiple antennas located at a certain distance from each other allows the router and client devices (smartphones, laptops) to effectively combat signal attenuation and reflections. Wi-Fi It operates in multipath conditions, where the signal reaches the receiver not only directly but also bounces off walls, furniture, and even people. Diversity helps the system select the best signal or combine them, which is critical in urban environments or offices with multiple partitions.
In this article, we'll take a detailed look at the physical principles of this technology, examine various implementation schemes, and provide practical advice on optimal antenna orientation for your equipment. Understanding how it works diversity of receiving antennas, will help you set up your network correctly without purchasing additional amplifiers.
Physical principles of signal diversity
The main enemy of indoor wireless communication is not distance, but interference and signal fading, known as fadingWhen a radio wave reflects off surfaces, it can arrive at the receiver with different phases. If the wave crests coincide, the signal is amplified, but if the crest of one wave meets the trough of another, they cancel each other out. It is to compensate for this effect that diversity is used, allowing the system to "see" the signal from different points in space.
There are several types of diversity, but spatial diversity is the most common in consumer routers. Antennas are spaced at a distance equal to a wavelength (usually half a wavelength, which for 2.4 GHz is about 6 cm). This minimizes the likelihood that the signal will be in a deep hole at the receiving point of both antennas. A critical parameter is the correlation between signals: the less the antennas correlate with each other, the more efficient the system is.
Furthermore, modern standards utilize polarization diversity. An electromagnetic wave has an oscillation vector, and antennas oriented vertically and horizontally receive signals with different polarizations. This is especially relevant given that we hold smartphones and tablets differently in our hands, and the orientation of their built-in antennas constantly changes.
β οΈ Attention: Diversity efficiency drops sharply if the antennas are too close to each other (less than a quarter wavelength). When modifying the router case, do not attempt to move the antenna connectors too close together, as this will degrade reception.
MIMO technologies and reception diversification
Technology MIMO (Multiple Input Multiple Output) has become the foundation of Wi-Fi 4 (802.11n) and later standards. It utilizes multiple antennas for both transmitting and receiving data. Unlike simple diversified reception, which selects the single best signal, MIMO enables the transmission of multiple data streams simultaneously over the same frequency using spatial coding.
Receive Diversity is a simpler mechanism often found in budget devices with two antennas, where one transmits and the other only receives, or both switch to search for the best signal. In systems with MIMO 2x2 or MIMO 3x3 All antennas are active simultaneously, which significantly increases channel throughput. For example, a router with three antennas can theoretically transmit three independent data streams.
It's important to understand the difference between actual streams and the number of antennas. Some manufacturers install three antennas on N300 routers, which physically only implement one or two streams (1T1R or 2T2R). In such cases, the third antenna may serve solely to improve reception or operate in a different frequency range if the device is dual-band.
Connection diagrams and antenna types
The router's internal architecture determines how diversity is implemented. Most modern models use omnidirectional whip antennas with a gain of 2-5 dBi. They radiate a signal in a "doughnut" shape around their axis. The connection diagram typically assumes that each antenna is connected to its own radio module or via a dedicated switch.
There are also systems that use external high-gain antennas (8-12 dBi and higher) connected via cable. In such systems, diversity can be achieved by installing antennas in different rooms or at significant distances (up to several meters) from each other. This allows for coverage of complex areas where a single access point cannot cope.
Below is a table showing the dependence of antenna configuration on the supported standard and speed:
| Configuration | Wi-Fi standard | Max. speed (2.4 GHz) | Description of the scheme |
|---|---|---|---|
| 1T1R | 802.11n | 150 Mbps | One antenna, no diversity |
| 2T2R | 802.11n/ac | 300 Mbps | Two antennas, basic MIMO |
| 3T3R | 802.11n/ac | 450 Mbps | Three antennas, improved diversity |
| 4T4R | 802.11ac/ax | 600+ Mbps | Four antennas, maximum efficiency |
When choosing equipment, it's worth paying attention not only to the number of antennas but also to the declared MIMO technology. Cheap routers with three antennas often feature a 2T2R technology, where the third antenna serves as a backup or decorative antenna for increased speed, but is beneficial for reception stability.
The Myth of the Third Horn
Why does a router have three antennas if the standard is 2x2? A third antenna is often used to support Beamforming technology or simply to improve reception in the 802.11n standard, where it can switch for diversification, even if transmission is only on two channels.
Antenna Orientation Guidelines for Maximum Coverage
Proper antenna orientation is the easiest way to improve your signal without investing in anything. Since rod antennas emit signals perpendicular to their axis (to the sides) rather than from the ends, their position directly impacts coverage. If the router is placed on the floor in the center of the apartment, the antennas should point vertically upward.
However, if you need to cover multiple floors or the signal needs to travel primarily horizontally, you can use a fan-shaped antenna array. For example, point one antenna vertically, a second horizontally, and a third (if present) at a 45-degree angle. This ensures better polarization compatibility with various client devices, which may be located in different planes.
It is not recommended to point all antennas directly at the same point or stack them parallel to each other. This creates interference zones and narrows the radiation pattern. Also, avoid shielding the antennas with metal objects, mirrors, or aquariums located directly behind them.
The Effect of Spacing on Speed ββand Stability
The main benefit of proper antenna diversity isn't so much peak speed as connection stability and reduced packet loss. In highly reflective environments (offices with glass partitions, apartments with mirrors), the signal constantly fluctuates. A diversity system allows the router to instantly switch to the antenna with the best signal quality or combine them, which is noticeable to the user as a lack of stuttering during video calls and games.
When using technology MIMO Connection speed directly depends on the signal quality of each antenna. If one antenna is located in an area of ββdeep shadowing or interference, the entire communication channel can degrade to single-antenna operation (SISO), which will halve or triple the speed. Therefore, uniform antenna distribution is critical to maintaining high data transfer rates.
The impact on range is also worth noting. While diversity doesn't increase transmitter power (it's limited by law), it does increase the sensitivity of the receiver. The router "hears" the weak response signal from your smartphone better, allowing it to maintain a connection over a greater range than a device with a single antenna.
Practical recommendations for installing a router
To maximize the antenna diversity potential, it's important to choose the right location for your router. The center of your apartment or office is ideal. Antennas should be positioned so that there's clear space between them. Avoid hiding the router in a cabinet or behind a TV, as this disrupts the antenna pattern and negates the benefits of multiple antennas.
If you're using a router with external antennas, make sure they're securely connected. A loose connector can cause one of the MIMO lines to stop working, putting the device in a reduced-performance mode. Check the antennas regularly for damage, especially if you have children or pets in the house.
In challenging cases where the standard configuration fails, you can experiment with replacing antennas with more powerful ones (with higher gain), but remember: gain is achieved by changing the shape of the radiation pattern. A high-gain antenna (e.g., 9 dBi) will "broadcast" further, but in the horizontal plane, which may degrade coverage on upper and lower floors.
βοΈ Checking antenna settings
β οΈ Attention: Equipment specifications and configuration interfaces may vary depending on the model and manufacturer. Always consult the official documentation for your device before making any configuration changes or replacing antennas.
Frequently Asked Questions (FAQ)
Will replacing antennas on a router increase internet speed?
Replacing antennas can improve signal strength (RSSI) and connection stability, which will indirectly impact speed if it was previously dropping due to poor connection quality. However, if your ISP offers a 50 Mbps connection, antennas won't improve it to 100 Mbps. They will only help you achieve the maximum possible speed under current conditions.
Is it possible to leave one antenna if there are two?
Technically, a router can operate with a single antenna, but you'll lose all the benefits of MIMO and diversity technology. Speeds may drop by half, and coverage and connection stability will be significantly reduced. Using a router with a single antenna is recommended only in extreme cases.
Does antenna length affect signal quality?
The antenna's physical length should correspond to the wavelength of the frequency it operates at (for 2.4 GHz, this is approximately 31 mm per quarter wavelength, but inside a plastic housing, the length may be longer due to the velocity factor). An antenna that is too long or too short without proper tuning will have a poor SWR (standing wave ratio), leading to power loss and transmitter overheating.
Why are the antennas on some routers non-removable?
Manufacturers make antennas non-removable to reduce device costs, reduce their size, and prevent users from damaging the connectors. This also ensures that users don't replace the stock antennas with incompatible ones, which could lead to equipment failure.