When you make a wireless device, you end up discussing antenna gain. But what is it actually?
If you look at an antenna datasheet, you will often see just one gain number in dB values. That is not fully accurate. It usually refers to dBi (power relative to an isotropic antenna), because the other common unit, dBd (power relative to a half-wave dipole antenna), is typically clearly marked when used.
Another detail is that this single value refers to maximum gain. One number is not enough to describe the whole story. Gain depends on frequency, and it also varies based on direction. If you have high gain in one direction, it means there is less gain in another direction, because a passive antenna does not create energy. It is also possible to have low gain in all directions, but that is not a good antenna either.
The benefit of maximum gain is that you can use it in calculations for approvals. Transmitted power combined with maximum gain gives the highest level of electromagnetic radiation in any direction from the antenna. This is monitored in approvals to protect users and other devices from excessive signals. The goal is that no device disturbs others.
An isotropic antenna is a theoretical point source that radiates equally in all directions. Since an antenna does not create energy, increasing gain in one direction always reduces it somewhere else. High-gain antennas are therefore very directive, like a TV Yagi antenna (Figure 1).
If we think of antennas like light bulbs, a spotlight is a good example of a directive source (Figure 2).
The closest approximation to an isotropic antenna is a traditional light bulb, even though it has zero light under its base (Figure 3). An isotropic antenna would have equal gain in all directions, but it does not exist in real life.
When integrating a ready-made COTS(Component off the shelf) antenna into a device, people often forget the effect of integration and mechanics on antenna performance. An antenna is not a regular component on a board. The integration must be designed to ensure that the antenna works properly.
For this reason, it is often easier to design a custom antenna, because it can be fitted to the mechanics instead of trying to adapt the mechanics to a COTS antenna. With ready-made antennas there are some tuning options, but depending on the case, the mechanical integration may limit performance.
Let’s think about light bulbs again. If you have a very directive bulb like a spotlight (Figure 4), and you place it in a matching fixture, they work well together.
If you have an omnidirectional, round bulb and place it inside a covered luminaire (Figure 5), the effect on the emitted light is clearly visible.
In a similar way, mechanics strongly affect an integrated antenna. I have often said that the antenna element design is only 20 to 40 percent of the work. The rest is managing the mechanics and the antenna surroundings.
An antenna needs space around it, just like a candle flame needs space for proper burning (Figure 6).
If you place metal or other conductive objects close to the antenna, it is like restricting the space of the flame (Figure 7). The antenna designer needs to stay up to date with mechanical changes, even small ones.
So what should you actually do with all this?
First, do not rely on a single gain number when evaluating an antenna. It is only a simplified reference point. The real performance depends on how the antenna behaves across directions, frequencies, and inside your device.
Second, treat the antenna as part of the whole system. The mechanics, layout, materials, and even small changes around the antenna will affect the result. In many cases, these factors have a bigger impact than the antenna element itself.
Third, think about the use case early. Where does the device need to perform? In which directions? In what environment? These questions define what kind of antenna performance is actually needed.
Antenna design is often approached late in the project, or treated like a throw-in component. That is where problems start.
At that point, if the performance is not good enough, the remaining options are limited:
These fixes rarely give optimal results.
At Radientum, antenna performance is not treated as a single number or a last step. It is treated as part of the system from the beginning.
This means:
In many cases, a custom antenna is not about making something complex. It is about making something that fits the product, instead of forcing the product to fit the antenna.