This post is a supplement to my other piece on dBm. I’ll explain here another specification relating to Wi-Fi coverage, the dBi, of which the high values generally indicate the so-called Wi-Fi high-gain antennas.
As it turns out, by itself, dBi generally doesn’t mean much as far as Wi-Fi is concerned. It’s something you shouldn’t pay a lot of attention to, if at all.
That is why most networking vendors don’t list this value in their home products, and those that do, do so solely for marketing purposes.
The bottom line is this: Don’t use dBi as a factor in choosing a home router or access point.
You can keep that knowledge and move on or continue with the rest — this post can be a fun read on a slow day.
What is dBi
To understand dBi, we first need to understand dB or decibel. Again, I detailed it in this post on dBm and Wi-Fi signal strength, but here’s the gist:
- dB is a logarithmic measurement. It doesn’t increase or decrease consistently but spirally.
- Other than the level of sound, dB is a logarithmic way to convey other material properties.
- dBm (decimal milliwatt) is an example where dB is used to measure power level or signal sensitivity.
- In the US, each Wi-Fi band, per regulations, has a max power level of 30 dBm (or 1 watt).
With that, dBi is decibel isotropic. It’s a logarithmic way to convey an object’s physical property measured in different directions.
Specifically, 0 dBi means the object emits radio waves equally in all directions. That’s like a sphere with the emitter right in the center.
Since we can’t see radio waves, you can imagine 0 dBi as how lights are emitted from a single source, like the sun or a light bulb. It goes out equally in all directions or omnidirectionally.
Theoretically, the moment you increase the dBi to higher than zero, the signal sphere starts to change its shape — it’s no longer a perfect orb. In reality, that depends.
That’s because, in our case, the object is a Wi-Fi antenna, and the property is the radio signals it pushes out. And the whole thing is very complicated.
The truth about high-gain antennas
It’s worth noting that antennas are not exclusive to Wi-Fi. All radio-based applications require these little poles to broadcast and receive signals.
In telecommunication, we often want to talk to a party in a specific direction.
For example, if you’re off-roading in a caravan, the first car generally wants to talk via radio to those behind it, and the last car wants to talk only to those in front of it.
And in this case, it makes sense to focus the antennas in two specific directions, behind and front, respectively. So, chances are the cars will use directional antennas.
With this type of antenna, the signals go farther in one direction (gain) at the expense of other (often opposite) directions (loss).
The higher the dBi value, the more focused the signals in the gain direction — the farther it can go — and the larger the area where there’s no signal at all.
Generally, directional antennas use 9 dBi or higher value, up to 24 dBi. But the number varies depending on the specific device or application.
You can think of directional antennas as your flashlight. The more you focus the light, the narrower the beam, and the farther it goes, but the less bright the area outside the beam is.
And when you use a flashlight, there’s no light behind you at all. Still, the flashlight has supposedly the same light output as when you take out the reflector and let the bulb emit omnidirectionally.
The gist of this is that there’s no “gain” in signals. You only take them from one direction to concentrate in another. The total signal output remains the same. Almost.
In reality, using focused signals always cause some loss of total output due to overheads. (A flashlight’s reflector doesn’t reflect 100% the amount of light that hits it — it absorbs some and turns that into heat.)
But in large-area coverage, directional (a.k.a high-gain) antennas are practical for specific applications like FM radio or cellular signals — depending on where you place the antennas, chances are you need to cover more in one direction than others.
OK, and that brings us back to Wi-Fi and its antennas.
Wi-Fi and antennas
All home Wi-Fi broadcasters — routers and access points — are omnidirectional (no-gain) for good reasons.
First, that’s because Wi-Fi signals are short in range due to the high frequencies — we’re talking about 2.4GHz, 5GHz, and 6GHz here. Omnidirectional allows the hardware to work most efficiently.
And secondly, omnidirectional is the best and safest design since it will fit all homes.
If you get a directional broadcaster, you need a professional to find out where and how to mount it in a particular place. The idea is impractical for vendors, even risky in customer satisfaction.
That said, all networking vendors generally try to make their home Wi-Fi broadcaster emit signals generically as a sphere. But this is no easy task — it’s close to impossible to have 0 dBi in Wi-Fi.
Wi-Fi antennas and dBi: It’s all in the FEM
The dBi value generally applies only to the antennas and doesn’t work the same in all vendors. That’s because how the signals come out of a router (or an access point) depends on the device’s Front-End Module (FEM).
(Typically, a FEM includes a few power and low-noise amplifiers and a handful of other hardware components. But that’s the kind of information I don’t want to get into.)
You can understand FEM as the Wi-Fi chip that works with the router’s firmware to determine how Wi-Fi signals come out of the hardware’s antennas.
The goal of a home Wi-Fi broadcaster is always to have the best combo of three elements: the most extensive Wi-Fi coverage, highest Wi-Fi signal strength, and the best compatibility. All are equally important.
(By the way, don’t forget Wi-Fi takes two — we need supported clients, too.)
And how FEM works with a particular antenna design within the constraint of 30 dBm power level to deliver that goal is a well-guarded secret of each vendor. That’s what makes one networking brand or specific router better or worse than others.
Router size matters
A common thing among Wi-Fi routers: using firmware to manipulate FEM and antennas requires a lot of processing power. That’s where a router’s CPU and system memory (RAM) comes into play.
And that’s also why if you want a powerful router with extensive coverage, you must find one of specific (large) physical size. Some even have internal fans — like the Asus RT-AX89X, Netgear RAX120, or Ubiquiti UDM.
That said, the antennas are just part of the equation. But all home Wi-Fi broadcaster comes with their own set of antennas, explicitly designed for the particular FEM.
Common dBi values of home routers: It’s kinda meaningless
Generally, none of the home Wi-Fi routers broadcasts signals as a perfect sphere — that’s not possible. Most of the time, the signal outputs are in the shape of an egg or a distorted orb.
As for the dBi value, that varies between 2 dBi and 6 dBi — there’s almost no situation where you have a perfect zero dBi. And then, the device’s FEM will work within that value to deliver the best signal output that’s as close to a sphere as possible. Again, the algorithm is a secret.
That said, revealing the dBi value in a home Wi-Fi router is purely for marketing purposes. For the number to make sense, the vendor needs to disclose how its FEM works, too — none does.
And that’s the reason why you shouldn’t care about dBi when it comes to picking a home Wi-Fi broadcaster.
Hardware vendors who focus on the broadcasting power, hence, the dBi tend not to do well in business — they often fail to deliver real-world performance to match the bogus antenna “gain.”
Amped Wireless is an example. A few years ago, the company made a big splash, advertising tens of thousands of square feet of coverage for its Wi-Fi 5 routers. It hasn’t done well since, not surprisingly.
Common questions relating to Wi-Fi antennas
And that brings us to a few frequently asked questions about the Wi-Fi antennas themselves.
Do more antennas mean better Wi-Fi speeds?
Not necessarily. Generally, a router needs one antenna for each band so that a dual-band router will have two antennas. After that, the additional antennas are for extra features, such as MU-MIMO, Beamforming, etc.
But even then, more antennas don’t necessarily mean more features. Also, the number of antennas doesn’t change the range of a router.
In other words, they change the type of coverage but not the range itself. So more antennas might mean faster speed grades, but not always so.
That’s because ultimately, it’s how the router’s FEM and firmware handles its antennas that matters. And a Wi-Fi connection’s speed takes two; the client also needs to support the feature and speed grade of the router for the goodness to happen.
In short, there’s no need to get too hung up on the number of the little poles sticking out of our Wi-Fi box.
My home is sprawling, can a third-party or directional antennas help?
The general answer is no. That’s because most vendors don’t make directional antennas for their broadcasters, and third-party ones don’t usually work as you might hope, if at all.
(On the other hand, you can use generic antennas at the receiving end — they are just passive pieces of metal. For example, if you get a TP-Link Wi-Fi adapter, you can use the antennas of an Asus on it — most of the time, they fit.)
There are directional Wi-Fi antennas, but most a made for outdoor applications. So, if you have a specific broadcaster that includes its purpose-built directional antennas, you can give that a try.
Keep in mind that, in this case, you might not get any signal from the device at all in some directions, even when you’re next to it.
How do I angle the antennas for best performance?
You can’t. At most, you can only make “different” performances.
Routers with external antennas generally have a section in their user manual about how they are supposed to be handled. But generally, they are supposed to stay vertical to deliver the intended coverage and performance.
Sure, you can change their positions (when possible) to manipulate a bit the shape of the coverage sphere mentioned above. Still, the result is generally unpredictable and varies from one router to another.
On top of that, the effect would take place at the end of the router’s range, where the signal is already too weak — the slight fluctuation will likely produce no meaningful Wi-Fi experience.
That is the reason why many routers with external antennas, like the TP-Link Archer GX90, don’t allow you to swivel them around at all. That’s not to mention that there are more routers with internal antennas.
That said, when it comes to antennas, don’t remove or collapse them — keep them extended. After that, feel free to put them at any angles you’d like. When unsure, leave them all vertical.
What’s more important is to place your Wi-Fi broadcaster at an elevated, open place.
There you go. There’s no need to get too hung up on the dBi when shopping for a new home Wi-Fi broadcaster. In most, if not all, cases, it’s insignificant. High-gain (directional) antennas are more relevant to non-Wi-Fi radio applications.
If you want to go with directional antennas with Wi-Fi, then dBi is essential, but in this case, you need to hire a professional and use specialized equipment.
However, in Wi-Fi, size does matter. You can’t pack a lot of algorithms into a small box without causing heat issues. So it’s unrealistic to expect a Wi-Fi router to be compact, good-looking, yet deliver top Wi-Fi speeds and extensive coverage. Not gonna happen.
Something has to give. It’s a matter of physics (and cost).