Continuing from the previous discussion, although antennas come in a wide variety of shapes and forms, they can be broadly categorized based on similarities.
By wavelength: medium-wave antennas, short-wave antennas, ultra-short-wave antennas, microwave antennas...
By performance: high-gain antennas, medium-gain antennas...
By directivity: omnidirectional antennas, directional antennas, sector antennas...
By application: base station antennas, television antennas, radar antennas, radio antennas...
By structure: wire antennas, planar antennas...
By system type: single element antennas, antenna arrays...
Today we will focus on discussing base station antennas.
Base station antennas are a component of the base station antenna system and an important part of the mobile communication system. Base station antennas are generally divided into indoor and outdoor antennas. Indoor antennas usually include omnidirectional ceiling antennas and directional wall-mounted antennas. We will focus on outdoor antennas, which are also divided into omnidirectional and directional types. Directional antennas are further subdivided into directional single-polarized antennas and directional dual-polarized antennas. What is polarization? Don't worry, we'll discuss that later. Let's first talk about omnidirectional and directional antennas. As the name suggests, an omnidirectional antenna transmits and receives signals in all directions, while a directional antenna transmits and receives signals in a specific direction.
Outdoor omnidirectional antennas look like this:
It's essentially a rod, some are thick, others are thin.
Compared to omnidirectional antennas, directional antennas are the most widely used in real-world applications.
Most of the time, it looks like a flat panel, which is why it's called a panel antenna.
A planar antenna mainly consists of the following parts:
Radiating element (dipole)
Reflector (base plate)
Power distribution network (feeding network)
Encapsulation and protection (antenna radome)
Previously, we saw those strangely shaped radiating elements, which are actually the radiating elements of base station antennas. Have you noticed that the angles of these radiating elements follow a certain pattern: they are either in a "+" shape or an "×" shape.
This is what we referred to earlier as "polarization."
When radio waves propagate in space, the direction of their electric field changes according to a certain pattern; this phenomenon is called the polarization of radio waves.
If the electric field direction of an electromagnetic wave is perpendicular to the ground, we call it a vertically polarized wave. Similarly, if it is parallel to the ground, it is a horizontally polarized wave. In addition, there are also ±45° polarizations.
Furthermore, the direction of the electric field can also be spirally rotating, which is called an elliptically polarized wave.
Dual polarization means that two antenna elements are combined within a single unit, forming two independent waves.
Using dual-polarized antennas can reduce the number of antennas needed for cell coverage, lower the requirements for antenna installation, and thus reduce investment, while still ensuring effective coverage. In short, it offers many advantages.
We continue our discussion on omnidirectional and directional antennas.
Why can directional antennas control the direction of signal radiation?
Let's look at a diagram first:
This type of diagram is called an antenna radiation pattern.
Because space is three-dimensional, this top-down view and front-to-back view provide a clearer and more intuitive way to observe the distribution of antenna radiation intensity.
The image above is also an antenna radiation pattern produced by a pair of half-wave symmetrical dipoles, somewhat resembling a tire lying flat.
Speaking of which, one of the most important characteristics of an antenna is its radiation range.
How can we make this antenna radiate further?
The answer is—by hitting it!
Now the radiation distance will be much greater...
The problem is, radiation is invisible and intangible; you can't see it or touch it, and you can't photograph it either.
In antenna theory, if you want to "slap" it, the correct approach is to increase the number of radiating elements.
The more radiating elements, the flatter the radiation pattern becomes...
Okay, the tire has been flattened into a disc, the signal range is extended, and it radiates in all directions, 360 degrees; it's an omnidirectional antenna. This type of antenna is excellent for use in remote, open areas. However, in a city, this type of antenna is difficult to use effectively.
In cities, where there are dense populations and numerous buildings, it's usually necessary to use directional antennas to provide signal coverage to specific areas.
Therefore, we need to "modify" the omnidirectional antenna.
First, we need to find a way to "compress" one side of it:
How do we compress it? We add a reflector and place it on one side. Then, we use multiple transducers to "focus" the sound waves.
Finally, the radiation pattern we obtained looks like this:
In the diagram, the lobe with the highest radiation intensity is called the main lobe, while the remaining lobes are called side lobes or secondary lobes, and there is also a small tail at the back called the back lobe.
Uh, this shape looks a bit like... an eggplant?
Regarding this "eggplant," how can you maximize its signal coverage?
Holding it while standing on the street definitely won't work; there are too many obstacles.
The higher you stand, the farther you can see, so we definitely need to aim for higher ground.
When you're at a high altitude, how do you aim the antenna downwards? It's very simple, just tilt the antenna downwards, right?
Yes, tilting the antenna directly during installation is one method, which we call "mechanical downtilting."
Modern antennas all have this capability during installation; a mechanical arm takes care of it.
However, mechanical downtilting also presents a problem—
When using mechanical downtilting, the amplitudes of the vertical and horizontal components of the antenna remain unchanged, resulting in severe distortion of the antenna pattern.
This definitely won't work, as it would affect signal coverage. Therefore, we adopted another method, which is electrical downtilting, or simply e-downtilting.
In short, electrical downtilting involves keeping the physical angle of the antenna body unchanged, and adjusting the phase of the antenna elements to change the field strength.
Compared to mechanical downtilt, electrically downtilted antennas exhibit less change in their radiation pattern, allow for greater downtilt angles, and both the main lobe and back lobe are directed downwards.
Of course, in practical use, mechanical downtilt and electrical downtilt are often used in combination.
After applying the downtilt, it looks like this：
In this situation, the main radiation range of the antenna is utilized quite effectively.
However, problems still exist:
1. There is a null in the radiation pattern between the main lobe and the lower side lobe, creating a signal blind spot in that area. This is commonly referred to as the "shadow effect."
2. The upper side lobe has a high angle, affecting areas at a greater distance and easily causing inter-cell interference, meaning the signal will affect other cells.
Therefore, we must strive to fill the gap in the "lower null depth" and suppress the intensity of the "upper sidelobe."
The specific methods involve adjusting the sidelobe level and employing techniques such as beamforming. The technical details are somewhat complex. If you are interested, you can search for relevant information yourself.
To learn more about antennas, please visit:
Post time: Dec-04-2025
