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Basic knowledge of electromagnetic wave propagation
Feb 28, 2018

Definition of radio waves

Radio waves are a form of signal and energy transmission. During propagation, electric and magnetic fields are perpendicular to each other in space and are perpendicular to the direction of propagation.

Of which: wavelength λ = C / f (where C is the speed of light, f is the operating frequency and λ is the wavelength.)

In the same medium, at different frequencies, the working wavelength of the antenna is different. The higher the frequency, the shorter the wavelength.

The electrical properties of the antenna correspond to the electrical length (wavelength). Physical length requires conversion.

Polarization of radio waves

Radio waves in space, the direction of its electric field is a certain law and change, this phenomenon is called the polarization of radio waves. The polarization of radio waves is determined by the trajectory of the electric field vector in space. If the direction of the electric field of the electric wave is perpendicular to the ground, we call it a vertically polarized wave. If the electric field of the electric wave is parallel to the ground, it is called a horizontal polarized wave.

Antenna polarization

Refers to the electric field vector trajectory in space.

Dual polarized antenna

Consists of two orthogonal radiation units.

1) Complementary (complete irrelevant. Orthogonal / 90 degrees) (planning work)

2) Quite (Balanced Work. + 45 / -45) (Competent work)

3) Efficient (XPD reduce loss) (focus on work)

Multi-path propagation

In the course of propagation, radio waves encounter obstacles (such as tall buildings such as hills, forests, ground or buildings) in addition to direct transmission, as well as reflection and diffraction. Therefore, the electromagnetic waves reaching the receiving antenna not only have direct waves, but also reflected waves, diffracted waves, and transmitted waves. This phenomenon is called multi-path transmission.

Because multipath propagation makes the distribution of signal field intensity complicated and fluctuating greatly, the polarization direction of the radio wave also changes (twists) due to the influence of multipath transmission. Therefore, in some places, the signal field strength increases and in some places Signal field strength weakened, in addition, different obstacles on the radio reflection ability is also different. In order to reduce the effect of multipath transmission, spatial diversity or polarization diversity is generally adopted for receiving.

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