Unguided (Wireless) Transmission Media

Signals travel through free space (air, vacuum, water) as electromagnetic waves, with no physical conductor.

1. Radio Waves (3 kHz - 1 GHz)

• Omnidirectional, propagate in all directions; penetrate walls
• Examples: AM/FM radio, TV broadcast, cordless phones, paging
• Pros: long range, penetrates buildings, simple
• Cons: interference, susceptible to eavesdropping, limited bandwidth

2. Microwaves (1 - 300 GHz)

• Unidirectional, line-of-sight; need aligned antennas
• Examples: cellular networks, satellite links, Wi-Fi, point-to-point towers
• Pros: high data rate, no cabling cost
• Cons: line of sight needed, affected by rain/weather, cannot penetrate buildings well

3. Infrared (300 GHz - 400 THz)

• Short range, line-of-sight; cannot pass through walls
• Examples: TV remotes, wireless keyboards/mice, IrDA
• Pros: secure within a room, no interference with other rooms
• Cons: very short range, blocked by obstacles, affected by sunlight

4. Satellite Communication

• Microwave relay through orbiting satellites (GEO, MEO, LEO)
• Examples: GPS, DTH TV, VSAT
• Pros: wide coverage, remote areas
• Cons: propagation delay, high cost

Summary

Medium	Range	Directionality	Penetration	Use
Radio	Long	Omni	Good	Broadcast
Microwave	Medium-long	Unidirectional	Poor	Cellular, satellite
Infrared	Very short	Directional	None	Remote controls

General advantages

Mobility, no cable installation, easy deployment in difficult terrain.

General disadvantages

Less secure, interference and noise, signal attenuation, weather dependence, lower reliability than fiber.