Very Low Frquency（VLF） 3 kHz-30 kHz Low Frequency（LF） 30 kHz-300 kHz Medium Frequency（MF） 300 kHz-3 MHz High Frequency（HF） 3 MHz-30 MHz Very High Frequency（VHF） 30 MHz-300 MHz Ultra High Frequency（UHF） 300 MHz-3 GHz Super High Frequency（SHF） 3 GHz-30 GHz Extremely High Frequency（EHF） 30 GHz-300 GHz

S band : 2 GHz C band : 4~5 GHz X band : 7~9 GHz Ku band : 10~15 GHz Ka band : 17~30 GHz

Parabola antenna is commonly used in satellite communication. The gain of parabola antenna \(G\) can be written as: \[G = \eta\left(\frac{\pi D}{\lambda}\right)^2\] where \(D\) is the diameter of the antenna, \(\lambda\) is the wavelength, and \(\eta\) is the aperture efficiency (\(0<\eta<1\))

To transmit the ditgital signal by radio wave, it is required to modulate the carrier wave. Digital modulation method can be categorized into 3 types: FSK and PSK are generally used in satellite communications.

Receiver antenna detects not only radio waves but alo various noises. The examples of the noise are: Noise temperature received by the antenna \(T_a\) is: \[T_a = T_s + (1-\eta)T_0\] where \(T_s\) is the noise temperature, \(T_0\) is the ambient temperature, and \(\eta\) is the radiation efficiency of the antenna.

Coherent detection is one of the method to demodulate the signal modulated by PSK. Coherent detection multiplies the signal by the carrier wave. The signal modulated by PSK can be written as: \[s(t) = A\cos{(2\pi ft+\phi)}\] where \(A\) is amplitutde, \(f\) is frequency, and \(\phi\) is the phase difference. Multiplying this signal by the carrier

Duplexer is the equipment that used when transmitter and receiver shares the same antenna. Duplexer allows signal to pass from transmitter to antenna, but does not allow the opposite direction. Also, the signal from antenna to receiver can pass, but the opposite direction not.

Diplexer is the equipment that combines two signal into one and divide one signal into two. Diplexer is used for multi-band system (which handles different frequency). The inner structure is as follows. The diplexer has high pass filter (HPF) and low pass filter (LPF). The signals come from right side of the image are combined.

Directional coupler is the equipement that distribute the signal for some ratio.