Diversity means two or multiple transmission paths are used to transmit the same information and the receiver output signals are selected or combined to reduce the effect of fading.
Diversity falls into;
1. Space diversity.
2. Frequency diversity.
3. Polarization diversity.
4. Angle diversity.
Space diversity and frequency diversity are more frequently used. Space diversity is economical and has a good effect.
Frequency diversity is often applied to multi-channel systems as it requires a wide bandwidth.
Space Diversity
In space diversity, signals have different multi path effect over different paths. Accordingly, two or more suites of antennas at different altitude levels may be used to receive the signals at the same.
The merit of space diversity is that frequency resources are saved. The disadvantage is that the equipment is complicated and two or more suites of antennas are needed.
The distance between the diversity antennas is 100 to 200 times the wavelength in frequently used frequency bands.
Space diversity can effectively solve the K-type fading caused by the interference of ground-reflective wave and direct wave, and the interference fading caused by troposphere reflection.
Frequency Diversity
In frequency diversity, signals at different frequencies have different fading characteristics in space transmission. Two or more microwave frequencies at certain frequency spacing may be used to transmit and receive the same information. Only one suite of antenna is required. The disadvantage is that the utilization rate of frequency bands is low.
