Radio frequency is short for RF, which is short for high frequency AC change electromagnetic wave.

Electromagnetic waves are actually a more familiar concept.

According to Maxwell's electromagnetic field theory: an oscillating electric field produces an oscillating magnetic field, and an oscillating magnetic field produces an oscillating electric field.

The electromagnetic field continuously propagates outward in space, forming an electromagnetic wave.

The following figure can roughly reflect this process, E represents the electric field, B represents the magnetic field.

The phase and amplitude of the electric and magnetic fields at the same position on the shaft will change with time.

In general, radio frequency (RF) is a general term for electromagnetic waves with oscillation frequencies between 300KHz-300GHz, and is widely used in radar and wireless communications.

2. RF basic characteristics

In order to describe a given radio frequency signal, four angles of frequency, wavelength, amplitude and phase can be used.

2.1 frequency and wavelength

The frequency of the electromagnetic wave is the frequency of the electromagnetic field oscillation.

The fluctuation has a period, and the frequency (f) is the number of periods in which the wave occurs in a given unit of time, in Hertz (Hz).

The following figure shows the waveform per unit time of a signal with a frequency of 10Hz.

The wavelength (λ) is the distance that the wave propagates in a period. In the case of a certain propagation speed, the wavelength is inversely proportional to the frequency, that is, λ = c/f.

RF of similar frequencies will interfere with each other, so there are organizations that specifically manage the spectrum to allocate the use of frequency bands to avoid mutual interference between applications and standardize the use of RF.

Due to attenuation and other factors, low-frequency electromagnetic waves can generally propagate longer distances than high-frequency electromagnetic waves, so they are often used for over-the-horizon radar.

High-frequency electromagnetic waves have high energy, strong penetration, and higher bandwidth. They are now also used in some line-of-sight communications to alleviate the problem of low-frequency band congestion, such as mmWave communications.

2.2 amplitude

The amplitude signal of RF is the measurement of the change of electric field oscillation in a single period. For sine wave, it can be represented by peak value ①, peak-peak value ② and root mean square value ③.