Zero Basics Antenna! After reading, you are half an antenna expert!

The following article is from the official account 5G radio frequency active passive filter antenna, the author is 5GThe antenna of the base station is more eye-catching than the base station itself. The words' antenna 'are not as simple as they appear

The following article is from the official account 5G radio frequency active passive filter antenna, the author is 5G

The antenna of the base station is more eye-catching than the base station itself. The words' antenna 'are not as simple as they appear. But we will do our best to say ithave toSimple and fun.

After reading this introduction to antennas, you will understand:

What exactly is an antenna?

How does the antenna transmit signals?

What are the key indicators of antennas?

As is well known, antennas are used by base stations and mobile phones to transmit signals.

The English word for antenna is Antenna, which originally means tentacles. The antennae are the two long filaments on the top of an insect's head. Don't underestimate such inconspicuous things. Insects transmit various social information through various chemical signals sent by these antennae.

Similarly, in the human world, wireless communication also transmits information through antennas, except for electromagnetic waves carrying useful information. The following figure is an example of communication between a mobile phone and a base station.

So what do antennas look like in practice? Due to different uses, there are too many forms of antennas, ranging from large dishes (parabolic antennas) that receive TV signals to small antennas hidden in mobile phones, which vary in shape due to their different functions.

When it comes to antennas, the most common thing most people see is the antenna of their home wireless router.

It's these stick like antennas that allow us to enjoy the same network speed as flying.

Just like a blind person touching an elephant, each classification method can only describe one side or one type of feature of the antenna. Only by combining all the features targeted by these classification methods can we see the full view of the antenna.

Symmetric oscillators are the most classic and widely used antennas to date.

The theory is still a bit boring. Hurry up, let's combine it with the actual object.

What is a oscillator in the real world like?

It's just this piece of metal... Half wave symmetric oscillator (non reduced)

Okay, in fact, the above one is just a traditional form of the oscillator, which also has N variant states:

A strangely shaped oscillator

Are you confused? If a oscillator is an antenna, then where is an antenna? Isn't the antenna we see in real life like this bird?

To be precise, the oscillator is not a complete antenna. The oscillator is the core component of an antenna, and its shape changes with the shape of the antenna.

And the form of the antenna is really too TM... Too much... Now...

In short, hundreds or thousands...

Although the shapes of antennas are diverse, they can also be roughly classified based on similarity.

If divided by appearance, there are several common ones, as shown in the following figure:

Whip antenna

Parabolic antennas, like huge pots, are magnificent. When transmitting, radar must concentrate its energy and radiate it in the direction it needs to be illuminated, and this shape is very suitable.

Parabolic antenna

Yagi antenna

PSYagi antennahave to20Yagi antenna

The following "pots" are smaller, which are microwave antennas used for transmitting and receiving microwave signals to transmit information. The wavelength of electromagnetic waves such as microwaves is very short and mainly propagates in a straight line. The transmitting and receiving antennas need to be aligned with each other to work, and are mainly used for transmission in wireless communication.

Our communication Wang is most concerned about, of course - communication base station antennas!

The base station antenna is a component of the base station antenna system and an important component of the mobile communication system.

The base station antenna is generally divided into indoor antenna and outdoor antenna.

Indoor antennas typically include omnidirectional ceiling mounted antennas and directional wall mounted antennas.

It's just a stick, both thick and thin.

The oscillator inside it looks like this:

Return to the main character of this article: directional antenna. To uncover the mysterious veil of this product, you need to open it up and see what's inside.

Compared to omnidirectional antennas, directional antennas are the most widely used in real work and life.

Most of the time, it looks like a board, so it is called a board shaped antenna.

The plate antenna mainly consists of the following parts:

• Radiation unit (oscillator)
• Reflective plate (bottom plate)
• Power distribution network (feed network)
• Encapsulation protection (radome)

The interior is empty, and the structure is not complex. It is composed of oscillators, reflector plates, feed network, and radomes. What are these internal structures for and how do they achieve the function of directional transmission and reception of signals?

All of this starts with electromagnetic waves.

The reason why antennas can transmit information at high speed is because they can emit electromagnetic waves carrying information into the air, propagate at the speed of light, and ultimately reach the receiving antenna.

This is like using high-speed trains to transport passengers. If information is compared to passengers, then the tools for transporting passengers are: high-speed trains are electromagnetic waves, and antennas are like stations, responsible for managing and dispatching the transmission of electromagnetic waves.

So, what is electromagnetic wave?

Scientists have studied the two mysterious forces of electricity and magnetism for hundreds of years, and ultimately Maxwell in the UK proposed that electric current can generate an electric field around it, a changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. This theory was ultimately confirmed by Hertz's experiment.

In such periodic transformations, electromagnetic waves radiate and propagate into space. For details, please refer to the article: "Electromagnetic waves cannot be seen or touched, and this young man's whims have changed the world.

As shown in the above figure, the red line represents the electric field, while the blue line represents the magnetic field. The propagation direction of electromagnetic waves is perpendicular to both the electric and magnetic fields.

An antenna is a "converter" - transforming guided waves propagating on a transmission line into electromagnetic waves propagating in free space, or vice versa.

The Function of Antennas

What is a guided wave?

Simply put, guided waves are electromagnetic waves on electrical wires.

So, how does the antenna send out these electromagnetic waves? After reading the following picture, you will understand.

The two wires above that generate electromagnetic waves are called "oscillators". In general, the size of the oscillator works best at half a wavelength, so it is often referred to as a "half wave oscillator".

With the oscillator, electromagnetic waves can be continuously emitted outward. As shown in the following figure.

With an electric field, there is a magnetic field. With a magnetic field, there is an electric field. In this cycle, there is an electromagnetic field and waves...

Electricity generated magnetism

Let's take another dynamic picture and experience this beautiful process:

The change in the direction of wire current generates a changing electric field

The half wave oscillator continuously propagates the electromagnetic wave source into space, but the distribution of signal strength in space is not uniform, like a circular tire.

But in fact, the coverage of our base station needs to be further in the horizontal direction, after all, the people who need to make calls are on the ground; The vertical direction is high above the ground, and there is no one who needs to brush Tiktok while flying in the air (the route coverage is another topic, I will talk about it next time). Therefore, in the emission of electromagnetic wave energy, the horizontal direction needs to be strengthened and the vertical direction needs to be weakened.

According to the principle of energy conservation, energy neither increases nor decreases. To increase the emitted energy in the horizontal direction, it is necessary to weaken the energy in the vertical direction. Therefore, we have to flatten the energy radiation pattern of the standard half wave oscillator.

How can we make the radiation distance of this antenna further?

Shoot it...

Pop it!

So how to flatten it? The answer is to increase the number of half wave oscillators. The emission of multiple oscillators converges at the center, weakening the energy at the edges, achieving the goal of flattening the radiation direction and concentrating energy in the horizontal direction.

In general macro base station systems, directional antennas are the most commonly used. In general, a base station is divided into three sectors and covered by three antennas, each covering a range of 120 degrees.

The above figure is a base station coverage plan for a certain area. We can clearly see that each base station is composed of three sectors, and each sector is represented by different colors, which requires three directional antennas to achieve.

So, how does an antenna achieve directional emission of electromagnetic waves?

Of course, this is not difficult for smart designers. Isn't it enough to add a reflection plate to the oscillator to reflect back the signal that should have been radiating towards the other side?

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In the figure, the lobe with the highest radiation intensity is called the main lobe, while the other lobes are called the side lobe or side lobe. There is also a tail on the buttocks, called the posterior lobe.

Uh, this design is a bit similar to... Eggplant?

For this' eggplant ', you can think about how to maximize its signal coverage?

Holding it while standing on the road is definitely not feasible, as there are too many obstacles.

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How can we shine down when we reach a high altitude? As smart as me, you must have thought of it. It's simple, isn't it okay to tilt the antenna down?

Yes, during installation, tilting the antenna directly is a method, which we call "mechanical tilting".

The current antenna has this ability when installed, with a robotic arm to handle it.

When using mechanical tilting, the amplitudes of the vertical and horizontal components of the antenna remain unchanged, resulting in severe deformation of the antenna pattern.

This definitely won't work, it's affecting signal coverage. So, we adopted another method, which is electric downward tilt, abbreviated as electric downward tilt.

In short, electric tilt down is to maintain the physical angle of the antenna body unchanged, by adjusting the oscillator phase of the antenna, and changing the field strength.

Take a dynamic picture and you'll understand:

Compared to mechanical downward tilt, the antenna pattern of electric downward tilt has little change, with a larger downward tilt degree, and both the front and rear lobes are facing downwards.

Of course, in practical use, mechanical down tilt and electric down tilt are often used in combination.

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However, there are still problems:

There is a lower zero depth between the main lobe and the lower side lobe, which can cause a signal blind spot at this position. Usually, we call it 'black under the light'.

The angle of the upper sidelobe is relatively high, which affects the distance far and can easily cause cross region interference. In other words, the signal will affect other cells.

So, we must strive to fill the gap of "zero depth at the bottom" and suppress the intensity of "upper sidelobes".

The specific method is to adjust the sidelobe level and use methods such as beamforming, which makes the technical details a bit complicated.

The knowledge in this area is really profound, so countless antenna experts are studying this topic, constantly developing and testing it.

If you are interested, you can search for relevant information yourself.

At this point, the explanation for the most important indicator of the antenna: "gain" is natural.

As the name suggests, gain refers to the antenna's ability to enhance the signal. Normally, an antenna does not require a power source, but only emits the electromagnetic waves transmitted to it. How can there be a "gain"?

In fact, whether there is a "gain" or not depends on who you compare with and how you compare.

As shown in the figure below, compared to the ideal point radiation source and half wave oscillator, the antenna can concentrate energy in the main lobe direction and send electromagnetic waves further, which is equivalent to enhancing in the main lobe direction. That is to say, the so-called gain is relative to the point radiation source or half wave oscillator in a certain direction.

So, how do we measure the coverage range and gain of the antenna's main lobe? This requires the introduction of another concept of "beamwidth". We refer to the range when the electromagnetic wave intensity on both sides of the centerline on the main lobe decays to half as the beam width.

Because the intensity attenuates by half, which is 3dB, the beamwidth is also known as the "half power angle" or "3dB power angle".

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Obviously, the presence of the back lobe disrupts the directionality of the directional antenna and needs to be greatly reduced. The energy ratio between the front and back lobes is called the "front to back ratio", and the larger the value, the better, which is an important indicator of the antenna.

The precious power of the upper sidelobe is transmitted to the sky in vain, which is also a considerable waste. Therefore, when designing directional antennas, it is necessary to minimize the upper sidelobe as much as possible.

In addition, there are some voids between the main lobe and the lower side lobe, also known as lower nulls, which cause poor signal near the antenna. When designing the antenna, it is necessary to minimize these voids as much as possible, known as "zero filling".

Well, this is what we mentioned earlier about 'polarization'.

As mentioned earlier, the propagation of electromagnetic waves is essentially the propagation of electromagnetic fields, and electric fields have directions.

If the direction of the electric field is perpendicular to the ground, we call it a vertically polarized wave. Similarly, parallel to the ground is a horizontally polarized wave.

Due to the characteristics of electromagnetic waves, signals propagated horizontally will generate polarization currents on the surface of the earth when they are close to the ground, resulting in rapid attenuation of the electric field signal. However, vertical polarization is less likely to generate polarization currents, thus avoiding significant energy attenuation and ensuring effective signal propagation.

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This is why I like to draw several forks in the antenna schematic, which vividly represent the polarization direction and the number of oscillators.

With a high gain directional antenna, can it be directly hung on the tower?

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The simplicity and convenience of electronic downscaling are not out of thin air, but have been achieved through the joint efforts of the industry.

In 2001, several antenna manufacturers came together to form an organization called AISG (Antenna Interface Standards Group), aiming to standardize the interface of electric tuning antennas.

So far, there are two versions of the protocol: AISG1.0 and AISG2.0.

With these two protocols, even if the antenna and base station are produced by different manufacturers, as long as they both follow the same AISG protocol, they can transmit control information of the antenna's downward tilt angle to each other, achieving remote adjustment of the downward tilt angle.

With the backward evolution of the AISG protocol, not only can the vertical downward tilt angle be remotely adjusted, but also the horizontal azimuth angle, as well as the width and gain of the main lobe, can be remotely adjusted.

Moreover, due to the increasing number of wireless frequency bands available to various operators and the increasing demand for antenna ports from technologies such as MIMO, antennas are gradually evolving from single frequency dual ports to multi frequency multi ports.

The principle of antennas may seem simple, but the pursuit of performance excellence is endless. This article only qualitatively describes the basic knowledge of base stations, and as for the deeper mysteries inside, how to better support the evolution towards 5G, wave after wave of communicators are still searching up and down.

Antenna testing darkroom

An excellent antenna cannot be achieved without good craftsmanship, reliable materials, and continuous testing.

Alright, this is the end of the article!

What can be seen here is definitely true love!

In fact, there is still a lot of knowledge about antennas, far beyond what is described in this article.

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Especially in the upcoming 5G, antenna technology innovation is the top priority, and major equipment manufacturers will definitely make every effort and contribute to the 5G antenna.

What kind of antenna black technology will emerge at that time? Let's wait and see!

5G antenna (large-scale antenna array)

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