Microwaves
Look up at a mobile tower and you will often see round, drum-shaped dishes near the top, all facing in different directions. Each one is pointed at a dish on another tower, kilometres away. Between them runs an invisible beam of microwaves.
1What microwaves are
Microwaves are sent and received by dish-shaped antennas. The dish sends them out as a narrow beam, like a torch, rather than in every direction like radio waves. These antennas are mounted on tall towers or buildings, so that they stay in line of sight above whatever is in between.
Change the tower height, or send the signal a different way. Drag sideways to turn.
Heights are to scale with each other; the distance between the towers is not.
With short towers, the hill blocks the beam: microwaves cannot pass through solid objects like walls, hills or mountains. Three ways round it: build the towers taller than the hill; put a repeater (relay) on the hilltop, which can see both towers; or bounce the signal off a satellite, which can see both from space.
Waves also get weaker as they travel, so on long routes repeaters are installed along the way to regenerate the signal — the same job a repeater does on a cable.
2Properties and uses
From your NCERT book, microwaves:
- Unidirectional: move in only one direction.
- Cannot penetrate solid objects such as walls, hills or mountains.
- Need line-of-sight: both antennas must face each other.
- Used in point-to-point (unicast) communication such as radar and satellite.
- Very large information-carrying capacity.
Satellites use microwaves to talk to dish antennas on the ground — for satellite TV, satellite phones and satellite internet. Radar, which finds aircraft and ships by bouncing waves off them, uses microwaves too.
Think of two friends with torches
3Advantages and disadvantages
- Very large information-carrying capacity.
- Covers long distances with towers, repeaters or satellites, without laying cable.
- A narrow beam goes only where it is pointed.
- Needs line of sight: tall towers are costly.
- Cannot pass through hills, buildings or walls.
- Heavy rain can weaken the signal.
4From the board papers
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(c) Microwaves — the question is NCERT’s own sentence about microwaves.
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(D) Microwaves. Radio waves are omni-directional, and infrared and Bluetooth are for short distances.
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Microwave — CBSE’s own marking scheme answer. For two cities this far apart the microwave link would run through towers with repeaters, or through a satellite.
5Check yourself
Why are microwave dish antennas mounted on tall towers?
Two microwave towers cannot see each other because a mountain is in between. Which of these solves it?