Basic knowledge of cell phone antenna (1)

ps. work needs, contact with the cell phone antenna, organize some basic knowledge for query

External requirements:

Antenna size is small, light weight, low profile, easy to carry, good mechanical strength .

Electrical performance requirements: the horizontal plane requires omnidirectional radiation direction map, wide bandwidth, high efficiency, high gain, by the surrounding environment has little impact on the human body radiation damage.

The cell phone antenna can be divided into two categories: external and built-in antenna according to the location.

Mobile phone antenna can be divided into two categories according to the traditional antenna unit form:

1. Monopole antenna

2. Spiral antenna

3. PCB printed spiral antenna

Above three kinds of external antennas

The following five kinds of antennas for the built-in antenna

4. Microstrip patch antenna

5. Slit antenna

6.

6.IFA antenna and inverted L antenna

7.PIFA

8.ceramic antenna

The advantages of external antenna are wide bandwidth, more stable receiving signal, simple manufacturing cost is relatively low; the disadvantage is that the antenna is exposed to the outside of the body is easy to be damaged, the antenna is close to the human body when the performance is caused by the deterioration of the antenna, it is not easy to add such as reflective layer and protective layer to reduce the radiation damage of the antenna to the human body. It is not easy to add reflective layer and protective layer to reduce the radiation damage of the antenna to the human body, at the same time, for the FDD system, the receiving and transmitting must use different matching circuits. Traditional external antennas are usually monopole antennas, which are simple to make but large in size and not portable.

Spiral antennas are generally used to reduce the size of the antenna (normal spiral), and spiral antennas printed on PCBs are now being used to obtain smaller external antennas with various shapes.

This antenna also has many kinds of deformation form, can realize multi-frequency, broadband requirements, there is a strong flexibility, so in the external antenna, this kind of antenna is more and more widely used.

Tie rod antenna: Generally a section of 1/4 wavelength spiral and a section of 1/2 wavelength spiral composition, the need for dielectric rod decoupling, used to realize the high gain of the cell phone, in the case of handheld, its gain can be increased by more than 6dB.

There is also a so-called dielectric antenna, medium-length dielectric antenna is a leaky antenna, its radiation characteristics for the end-shooting, and here the dielectric antenna may be similar to the monopole antenna antenna, which radiates signals through the principle of the dielectric resonator work, you can make the antenna volume is greatly reduced, if so, the antenna's Q value is high, the bandwidth is narrow, the broadband and multi-frequency is not easy to realize, there should not be This antenna has a high Q, a narrow bandwidth, a broadband and multi-frequency are not easy to realize, there should not be much application.

Here is the basic introduction:

Dielectric oscillator antenna made of high dielectric constant, low loss materials, the benefits are: small size, bandwidth can be adjusted within 1% to 10%, no conductor loss, high antenna efficiency, can produce a variety of modes, the lower modes of bandwidth is better, the higher modes of the gain is large.

If the dielectric oscillator is small enough, it can be built into a cell phone.

Tie rod antenna Although the effective gain is high and the electrical performance is good, but its structure is complex, and it needs to use memory metal as the material, so it is more expensive, except for a few places such as North America, the application is relatively small, and we don't consider using it.

Helical antennas have become the mainstream of external antennas because of their good radiation characteristics, small size, and easy bandwidth expansion, but their size is still large, and their shape is fixed, which is not suitable for special requirements such as cell phone shape design.

PCB spiral antenna than the ordinary spiral antenna volume is smaller, the shape of the antenna is flat characteristics, at the same time, this kind of antenna design has a strong flexibility, the application of more and more.

Spiral antennas are still the first choice for external antennas, followed by PCB spiral antennas.

Characteristics of the built-in antenna:

It can be made very small and not easy to be damaged; it can be placed in the phone away from the human brain side, and in the part near the human brain with a reflective layer, a protective layer to reduce the antenna radiation damage to the human body.

It can be installed more than one, it is very convenient to group the array, so as to realize the intelligence of the cell phone antenna, which is very useful for the future mobile communication system.

Built-in antennas are particularly varied in form, including microstrip patch antennas, slit antennas, IFA antennas and inverted L antennas, PIFA, ceramic antennas, and so on.

PIFA is one of the most used built-in antennas nowadays, which is evolved from inverted F-line antenna, and has the features of small size, high gain, low profile, and relatively wide bandwidth, and it is the antenna that is used the most in cell phone antennas.

The patch antenna and the slit antenna are also the most used built-in antennas, and the patch antenna and the slit antenna are interchangeable through the Balbiene principle.

Generally, ceramic antennas are used only when the antenna size is extremely small, which is now the case in Bluetooth devices. Their low gain, low efficiency, narrow bandwidth, and high cost make their use in cell phones a long way off.

In general, the external antenna's VSWR can be 2, and the gain can be 0-1dBi.

For the built-in antenna, the VSWR can be 3, and the gain can be 0-1dBi.

In the cell phone antenna, the antenna gain is not important, and the average effective gain is important, and the basic conclusion is that the external antenna has an average effective gain 2dB larger than the average built-in antenna. The basic conclusion is that the average effective gain of an external antenna is about 2dB greater than that of a typical built-in antenna. The efficiency of the built-in antenna is not up to the level of the external antenna.

When choosing a cell phone antenna, you can't be deceived by the PEAK GAIN, the actual average effective gain is less than this value, and is closely related to the cell phone design.

External antenna cell phone antenna price is about 2.5-4 dollars.

And built-in antennas are more expensive, ranging from about $3-20 dollars.