Microwaves are radio signals with a very short wavelength. Microwave signals can be focused by antennas just as a searchlight concentrates light into a narrow beam. Signals are transmitted directly from a source to a receiver
site. Reliable microwave signal range does not extend very far beyond the visible horizon.
If microwave signals were visible to the eye, cities would be seen to be crisscrossed by microwave transmissions carrying important signals. Any type of information that can move over telephone wires or coaxial cables can be transmitted over a microwave circuit as efficiently as through the wires and cables they supplement.
Microwaves and power
The ability to focus microwave signals into narrow beams results in very high antenna gain. Antenna gain increases the effective-radiated power of a microwave signal much as the reflector in a flashlight produces a tight beam of light powerful enough to illuminate distant objects. The most common microwave-antenna focuses the signal by reflecting it from a parabolically-curved reflecting surface sometimes called a dish.
High antenna gain means that microwave transmitters need not be extremely powerful to produce a strong signal. A transmitter rated at 10 watts or less, using an antenna that concentrates the signal toward its target, can produce a received signal as strong as if thousands of watts were scattered in all directions.
The lower-powered microwave signals used by communication transmitters are usually produced by solid-state devices. The Gunn diode is an example. When supplied with voltage from a well-regulated power supply these devices reliably produce a few watts of microwave signal