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Microwave Communication

Microwave Path Loss

Microwave communications systems must be carefully engineered if they are to provide reliable communications. Engineers can predict the signal loss in decibels (dB) for a given signal path. They are then able to specify the transmitter power, total antenna gain, and receiver sensitivity required for the circuit. Additional signal or gain can be specified to protect against most fades.

As an example, suppose that a proposed path for a microwave relay system between a radio-station studio and a remote transmitter site is predicted to have a circuit loss of 110 dB. If the system design provides a safety cushion of 30 dB against the possibility of rain fade, the total gains and losses in the system must equal at least +140 dB. If the calculations fall short of this target by 10 dB, for example, the engineer can increase the power of the transmitter by a factor of 10, or increase the gain of one or both of the other antennas by 10 dB, or increase the receiver sensitivity, by 10 dB. Any combination of improvements that will add to 10 dB will provide the desired performance.

Microwave communication is nearly 100% reliable, in part because the circuits have been engineered to minimize fading and in part because computer-controlled networks often reroute signals through a different path before a fade becomes noticeable.


Resources

Books

ARRL. The Satellite Experimenter's Handbook. Radio Society of Great Britain: American Radio Relay League, 1990.

Hobson, Art. Physics: Concepts and Connections. Upper Saddle River, NJ: Prentice-Hall, Inc., 1995.

Ostdiek, Vern J., and Donald J. Bord. Inquiry Into Physics. 3rd ed. St. Paul, MN: West Publishing Company, College & School Division, 1995.

RSGB. Microwave Handbook. Vol. 1-3. Radio Society of Great Britain: American Radio Relay League, 1989, 1991, 1992.

Other

ARRL. The ARRL UHF/Microwave Experimenter's Manual. Radio Society of Great Britain: American Radio Relay League, 1990.


Donald Beaty

KEY TERMS

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Bandwidth

—Range of frequencies available for a dedicated purpose.

Coaxial cable

—A concentric cable, in which the inner conductor is shielded from the outer conductor; used to carry complex signals.

Decibel

—A unit of measurement of the intensity of sound, abbreviated dB.

Ducting

—Trapping a radio signal so it follows the earth's curvature.

Inversion

—An atmospheric condition in which air temperature increases with increasing altitude, instead of the usual decrease.

Parabolic

—Shape based on the parabola, a conic section from mathematics.

Passive reflector

—Surface used to reflect a signal.

Propagation

—Basis for the transmission of a signal.

Radar

—A method of detecting distant objects based on the reflection of radio waves from their surfaces.

Spatial diversity

—Reduction of interference by maintaining physical separation.

Additional topics

Science EncyclopediaScience & Philosophy: Methane to Molecular clockMicrowave Communication - Microwaves And Power, Spatial Diversity, Microwave Propagation, Microwave Path Loss - Microwave transmitters, Satellites and microwaves