Microwave Basics

AM - Amplitude modulation

FM - Frequency modulation

PM – Phase modulation

ASK – Amplitude Shift Keying

FSK – Frequency Shift Keying

PSK – Phase Shift Keying

QAM – Quadrature Amplitude modulation

Dispersion

Electromagnetic signal propagating in a physical medium is degraded
because the various wave components (i.e., frequencies, wavelengths)
have different propagation velocities within the physical medium:
• Low frequencies have longer wavelength and refract less
• High frequencies have shorter wavelength and refract more

Humidity/Gas

Multipath/ducting

Multipath occurs when there is more then one beam reaching the receiver with different amplitude or phase

Multipath transmission is the main cause of fading in LOW frequencies

Atmospheric (refraction)

Terrain

Climatic

Rain attenuation

Refers to scenarios where signal is absorbed by rain, snow, ice
• Absorption becomes significant factor above 11GHz
• Signal quality degrades
• Represented by “dB/km” parameter which is related the rain
density which represented “mm/hr”
• Rain drops falls as flattened droplet
 V better than H (more immune to rain fading)