The antenna is quite common in EMC, RF test, and measurement, and the common antenna is as follows:
1, double cone antenna:
Commonly used in RSE alternative test.
Common work frequency band: 30MHz ~ 300MHz
Double cone antenna
2, alignment antenna:
Commonly used in radiation venue NSA calibration.
Common work frequency band: 30MHz ~ 1GHz
Alternate
3, the alignment of the antenna:
Commonly used in radiation harassment / radiation stray low frequency test.
Common work frequency band: 30MHz ~ 3GHz
Alternative week antenna
4, three ring antenna:
Commonly used in magnetic field radiation testing of lamps.
Common work frequency band: 9kHz ~ 30MHz
Three ring antenna
5, speaker antenna:
Commonly used in radiation harassment / radiant stray high frequency test.
Common work frequency band: 1GHz ~ 18GHz
Trumpet antenna
6, Icon Antenna:
Commonly used in the measurement of site attenuation and antenna coefficient.
Common work frequency band: 30MHz ~ 4GHz
Dipole antenna
7, ring antenna:
Commonly used for low frequency magnetic field testing.
Common work frequency band: 9kHz ~ 30MHz
Annual line
In the EMC and RF test, the following basic concepts need to be mastered:
The polarization direction of the antenna
There is often a customer asking what is vertical, and the antenna radiates electromagnetic waves to the surrounding space. Electromagnetic waves are composed of electric fields and magnetic fields. It is stipulated that the direction of the electric field is the direction of the antenna polarization. The antenna typically used is monolarized. The figure below shows two basic single-polarization.
The polarization direction of the antenna
Wave-flap width
The beam width refers to the angle between the two semi-power points in the direction of the antenna peak response, and the beam width has two components of the E-plane and the h, and the two are not necessarily completely equal. If the gain design of an antenna is Positive, its beam width and gain are often just the opposite. The direction map usually has two or more petals, wherein the maximum amount of radiation intensity is called a main flap, and the remaining valves are referred to as a sub-flap or a side lobe. On both sides of the maximum radiation direction of the main flap, the angle between the two points of the radiation intensity is reduced by 3 dB (half of the power density) is defined as a width width (also known as beam width or the main lobe width or half power angle). The narrower the width width, the better the direction, the farther the action distance, the stronger the anti-interference ability.
Wave-flap width
Antenna gain
The gain refers to the ratio of the power density of the actual antenna and the ideal radiation unit at the same point at the same time. It describes an antenna to turn the extent of the input power concentration. The gain is clearly related to the antenna direction map, the narrighters the direction of the direction, the smaller the vice, the higher the gain. It can be used to understand the physical meaning of the gain - to generate a certain size signal at a certain distance, if an ideal non-directional point source is used as the transmit antenna, the input power is required, and the gain is G. When a certain orientation antenna of DB = 20 is used as a transmit antenna, the input power is only 100/20 = 5W. In other words, the gain of an antenna is in line with the radiation effect in its maximum radiation direction, and the input power is magnified in a multiple of the no-directional ideal point source.
Antenna coefficient (AF)
The antenna coefficient in the free space is the parameter inherent in the antenna itself. The antenna coefficient represents the relationship between the radiation field and the antenna input voltage, the AF and the gain have the following relationship:
AF = E / U
(E- incident on the electric field strength of uniform and surface wave on the receiving antenna reference plane; U-receiving antenna output voltage)
bandwidth
The bandwidth refers to the frequency coverage of the antenna. If the bandwidth is represented by a portion of the antenna rated frequency range, the bandwidth of the non-resonant antenna is greater than the bandwidth of the resonant antenna, the bandwidth of the low gain antenna is greater than the bandwidth of the high gain antenna, for broadband , Balance the antenna that does not balance the converter or matching the network, its bandwidth is greater than the antenna coefficient.
impedance
The impedance of the antenna is usually considered, because all EMC test equipment is designed to 50Ω, the impedance of EMC antennas is also designed to be designed in its frequency range to be close to 50Ω, but the tester should also conscious impedance The possible problems brought by the match, especially the low frequency magnetic field ring antenna, the impedance of the antenna tends to change with the frequency, but many low-frequency ring antennas do not match the network to compensate this change.
Resident waveby (VSWR)
The standing wave ratio is an indirect parameter that measures whether the two RF device impedances match. VSWR is very important to most users. This has several complicated reasons. In simple, in general, the impedance exhibited by the feeder is the amount of the feeder to impedance and load impedance, so on both ends of the feeder There may be no matching of impedance, so that most signals will reflect at the load, and then reflect again along the feedth, when accurate measurements are required, or when the signal source does not match the impedance When the loss of the feeder is very heavy, VSWR will become a problem.
size
The size is a very important antenna feature. The antenna needs control and movement limits the actual size of the antenna. It is necessary to use antenna in the shield room to limit the maximum size of the antenna. It is necessary to reduce the ground or to the surrounding object. The coupling will also affect the size, but in contrast, it is desirable to have a good low frequency response, high gain or bandwidth, and increase the size of the antenna.
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