Interpretation of several important concepts of satellite antenna

This article simply interprets the antenna 4 Important concepts , Antenna standing wave ratio , Antenna gain , Antenna polarization mode , Antenna axial ratio .

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1： Antenna standing wave ratio

     The probability of antenna standing wave ratio is proposed to explain the transmission efficiency of antenna by using the concept of standing wave ratio . The standing wave ratio of the antenna determines the ability of the signal to be transmitted to the antenna .
     The standing wave ratio is positively correlated with the reflection of the signal . The larger the reflection coefficient, the larger the standing wave ratio . When there is no signal reflection, the standing wave ratio is 1. When there is signal reflection , If the reflected voltage and the signal voltage are in the same phase , Then the sum of the two voltages will form a antinode ; If the phase of the reflected voltage is opposite to that of the signal voltage , Then form a trough . In Bobbie = Antinode voltage / Trough voltage .
     The antenna standing wave ratio can be used to evaluate the efficiency of signal transmission to the antenna , When the antenna standing wave ratio is 1 when , All signals are transmitted to the antenna without reflection （ If it resonates with the antenna , Theoretically, it can all radiate out ）

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2： Navigation second solution antenna gain

     Antenna gain refers to the comparison between an antenna and an ideal antenna , Under the same conditions , The ratio of energy radiated to the same position in space . The antenna gain determines the ability of the antenna to transmit signals .
     for example ： Ideal antenna , Input power 1W when , You can go to space A Point radiation 1W Energy . The actual antenna input power is 1W when , It can radiate into space 10W Energy . Then the gain of the antenna is 10 times . If the gain is expressed in logarithm ： gain A=10log（ gain ）. If the antenna participating in the comparison is an ideal antenna that transmits power in a sphere to the whole space , Then the gain unit is dBi; If the participating antenna is an ideal dipole antenna （ To space 2 Transmit power in a fixed direction ）, Then the unit of antenna gain is ：dBd

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3： Navigation second solution antenna polarization mode

     The standing wave ratio of the antenna determines the ability of the signal to be transmitted to the antenna , The antenna gain determines the ability of the antenna to transmit signals , The polarization of the antenna determines the change form of the electromagnetic wave radiated by the antenna in space . Due to the specific polarization form of the antenna , Only electromagnetic waves with specific polarization mode can be received , And the polarization mode of electromagnetic wave will change after encountering obstacles , Therefore, the polarization of the antenna helps to suppress the mutual interference of electromagnetic waves propagating in multiple paths .
     The electromagnetic wave radiated by the antenna at a long distance is shear wave , The direction of electric field and magnetic field is vertical , The propagation direction of the electromagnetic wave and the electric field are perpendicular to the plane of the magnetic field . If the plane where the electric field and magnetic field are located is called the plane A, According to the propagation direction of electromagnetic wave , The electric field vector is in the plane A Different ways of change in , The polarization mode of antenna can be divided into the following categories .

a. Linear polarization

     The electric field vector always changes along a line .

b. Circular polarization HCP

     The electric field vector is always circling , And the circle is close to the circle . Depending on the direction of rotation , It is also divided into left-handed circular polarization and right-handed circular polarization .

c. Left circular polarization LHCP

     The electric field vector rotates counterclockwise around the standard circle

d. Right-handed circular polarization RHCP

     The electric field vector rotates clockwise around the standard circle

e. Elliptically polarized

     The electric field vector is always circling , And the circle around is close to the ellipse . Depending on the direction of rotation , It is also divided into left-handed elliptical polarization and right-handed elliptical polarization .

f. Left handed elliptical polarization

     The electric field vector rotates eccentrically

g. Dextral elliptical polarization

     The electric field vector rotates in a clockwise ellipse

4： Navigation second solution antenna axis ratio

     The axis ratio refers to the ratio of the major axis to the minor axis of the ellipse . Axial ratio of antenna , It refers to the elliptical polarization mode of the antenna , The ratio of the major axis to the minor axis of the electric field vector ellipse . Introduce the probability of antenna axial ratio , It can not only quantify the roundness of the ellipse . Also take circular polarization , Important ways of elliptical polarization and linear polarization . Because standard lines and circles do not exist . Therefore, when the defined axial ratio is much greater than a certain value , The elliptical polarization is called linear polarization . When the axial ratio is less than a certain value , The elliptical polarization is called circular polarization .