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Antenna parameters and measurement methods

Jan 25, 2019

The antenna parameters

Antenna pattern: the relationship between electric field intensity and space Angle is drawn as the pattern of field intensity-angle variation.


Main lobe width: the Angle between two points when the field intensity decreases from the maximum value of the main lobe to 0.707 times of the maximum value.


Sidelobe level: ratio of sidelobe maximum value to primary lobe maximum value (dB)


Directivity coefficient: under the same radiated power, the square of the electric field intensity generated by the antenna at a certain point is the ratio of the square of the electric field intensity generated by the power supply antenna at the same point.


Antenna efficiency: refers to the ratio of the total power radiated by the antenna to the input power.


Antenna gain: the ratio of the square of the electric field intensity generated by the antenna at a certain point to the square of the electric field intensity generated by the power supply antenna at the same point under the same input power.


Effective aperture: ratio of the total power received by the antenna to the power density of the incident field.


Radiation resistance: the radiated power of the antenna divided by the square of the effective value of the input current.


Input impedance: the ratio of the input voltage of the antenna divided by the input current.


Phase center of the antenna: after the electromagnetic wave radiated by the antenna leaves the antenna for a certain distance, its equiphase surface will be approximately a spherical surface, and the spherical center of the spherical surface is the equivalent phase center of the antenna.


Antenna parameter measurement

Standing wave ratio test


Directly measure the maximum and minimum point field intensity of "line" standing wave


Rho = Emax/Emin


Antenna gain test


1. The comparison method


The comparison method is to measure the antenna gain by comparing the gain of the antenna under test with the standard gain of the known antenna.


G = Gs + Px - Ps


G is the antenna gain to be measured


Gs is the standard antenna gain


Px is the receiving power of the antenna under test


Ps is the received power of standard antenna


2. Two identical antenna methods


Both transmit and receive antennas use the antenna under test


G = 0.5 (20 lg (4 PI * R/length_wave) - 10 lg (P0 / Pr))


3. Three-antenna method

                                          

Antenna

There are three pairs of transceiver antennas, measuring three times in total.



4. Beam width method


5. Orientation diagram integration




Measurement of axial ratio


The source antenna adopts linear polarization antenna with good orthogonal polarization.Slowly rotate the source antenna and record the maximum and minimum values of two levels


AR = [(Pmax1 - Pmin1) + (Pmax2 - Pmin2)] / 2

Small Measurement Antenna

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