After the read of the active antenna vs passive antenna, you will learn about what is an active antenna, what is a passive antenna, and the differences between an active antenna vs passive antenna.
Among the general antennas containing only metal and media, there is an active antenna if there is an active device such as a crystal triode, a tunnel diode, or a beam diode. It improves the performance of electricity small antenna. Active devices in the active antenna can be directly loaded into the antenna, or the antenna and amplifier can constitute an antenna system.
The ordinary antenna is equipped with an active device, which can improve the impedance of the electric mini line, the exhibition frequency band, improve the noise characteristics of the system, etc., the active antenna helps miniaturize the antenna.
Active devices in the active antenna can work in both linear and non-linear conditions, and the mutual principles apply to the former and are not applicable to the latter.
The picture below shows the active antenna input impedance
In the formula R1, C1, L1 are the resistance, capacitance, and inductance of the antenna; S = IC / VBE is the mutual exchange of transistors; β = IC / IB is a magnification of current amplification. Usually β »1, the input resistance of the active antenna
The resonant frequency of the Ri = R1 + 1 / S antenna is
The resonant frequency of the passive antenna is in the formula.
Therefore, the active antenna is reduced by a passive antenna such as a hologram, and the input resistance is improved so that the bandwidth of the antenna is wide.
There is a source antenna with the amplifier, and if the input impedance of the amplifier is much smaller than the impedance of the antenna, the antenna can obtain an output current independent of the frequency. If the design is correct, the bandwidth can reach several times.
The working principle of an active antenna is actually a high impedance of a short antenna (or rod antenna) that matches the low impedance input by the receiver. If the length of the antenna is less than 10 meters, increasing the length of the antenna reduces the impedance, and the signal level is also enhanced. So the long-line antenna is the easiest and most effective antenna.
If the active antenna is applied to the short antenna, it is necessary to drop the impedance of the antenna system, and the active antenna also enlarges the small signal to enlarge the output signal level close to the strength of the long antenna.
Since there is such a good source, why isn’t everyone using active antennas? There are two main reasons here:
- Active antenna length is generally shorter and close to and fixed at the position of the receiver, so it is easy to detect more interference than long-line antennas (such as a clock, television, etc.).
Once zoomed in, these interferences are also amplified, and the antenna can be moved to obtain the best reception effect. In the worst case, the active antenna will completely lose effectiveness due to disturbance.
- The most serious problem is intermodulation and distortion.
A well-designed receiver is at the beginning of the signal path and always has a good filter to ensure that the weak signal will be overwhelmed by the unnecessary signal. The magnitude of the active antenna is not perfect.
If the signals F1 and F2 are mixed at the input of the amplifier, the frequency signal, the difference frequency signal, and the harmonic signal are obtained at the output. The receiver cannot distinguish between these signals from the real radio signal.
For example, at night, the 7MHz signal is strong, and the 14MHz signal is weak. Due to harmonic distortion, some 7MHz signals will appear in the vicinity of 14 MHz when using the source antenna. Similarly, intermodulation can also cause the receiver to receive some false signals.
The working principle of an active antenna is actually a high impedance of a short antenna (or rod antenna) that matches the low impedance input by the receiver. If the length of the antenna is less than 10 meters, increasing the length of the antenna reduces the impedance, and the signal level is also enhanced. So the long antenna is the easiest and most effective antenna.
Active antenna vs passive antenna conclusion
Problem 1:
In addition to changing the installation location, it is impossible to improve the technique of technology.
Problem 2:
Can be improved by selecting an active antenna with a good filtering device.
The filter must be adjustable and the bandwidth of the filter is consistent with the frequency band required. Typically adjust the filter while also requires adjusting the gain of the amplifier, due to distortion and intermodulation, the appropriate reduction in gain actually improves the quality of the signal.
Overall, the difference between the active antenna vs passive antennas is still very large.
First, the difference between active antennas vs passive antennas
Active antenna vs passive antenna definition
Active antenna:
Internal integration of receiving antenna module, low noise amplification module, power supply module. It is powered by a fixed low pressure regulated power supply, and the passive antenna generally includes receiving antenna module.
Passive antenna:
An antenna without any active devices is suitable for communication technology.
Active antenna vs passive antenna application
Available antenna:
Integrating the radio frequency portion of the base station into the inside of the antenna, using a multi-channel radio frequency and antenna stage, realizing the spatial beam excipient, and completing the transmission and reception of the RF signal. The system has a high reception sensitivity.
Passive antenna:
The passive antenna has the ability to reduce the internal loss of the RF and microblogging devices but does not add noise, its system receives sensitivity.
Active antenna vs passive antenna outline
Available antenna:
Integrated receiving antenna module, low noise amplification module, power supply module, etc., can see an amplifier of antenna, reduce signal-to-noise ratio.
Passive antenna:
For a relatively simple metal body, it is based on log interval antennas, flat spiral antennas, coil antennas, screw antennas.
Second, the active antenna vs passive antenna, who occupies mainstream?
The passive antenna currently still occupies a large sector, but with the in-depth 5G construction, the active antenna is also continuously increased for multi-frequency antennas and Massive MIMO.
The 5G signal band is improved, and the use of Massive MIMO technology is not only large size of the number of 5G antennas. The antenna and radio module integrated active antenna will also be an important direction.
The active antenna can achieve adaptive adjustment of each antenna vibrator phase and power, significantly improve the spatial resolution of the MIMO system, improve the spectral efficiency, and enhance network capacity, in addition, higher efficiency and better efficiency and better through-beam excipient technology Signal coverage.
Therefore, the activation of the antenna is the trend of the 5G era and the mainstream of future development.
Mobile phone active antenna vs passive antenna test
Currently paying attention to the test of radiation performance in mobile radio frequency performance testing, this radiation performance reflects the final transmitting and reception performance of the phone.
At present, there are two main methods to investigate the radiation performance of mobile phones:
One is to determine the radiation performance of the antenna is currently a more traditional antenna test method, called passive test;
The other is to test the radiation power and reception sensitivity of the phone in a particular microwave referred to as an active test. OTA (over the air) test is an active test.
The passive test focuses on the radiation performance of mobile phones from the radiation parameters of the antenna of the mobile phone antenna.
Although the passive test considers the impact of the whole machine environment (such as antenna peripheral device, opening, and closed cover) on antenna performance, the ultimate radiation transmits power and reception sensitivity after the antenna and the whole machine, from the passive test data unable Directly learned that test data is not very intuitive.
The active test focuses on the radiation performance of the mobile phone from the transmit power and reception sensitivity of the mobile phone.
The active test is the emission power and reception sensitivity of the whole machine in each direction of the three-dimensional space in a particular microwave dark chamber, which can directly reflect the radiation performance of the mobile phone.
To put it bluntly, the passive test is not booting, and the active test is the test under start-up conditions.
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