Microwave

Microwaves are a specific form of electromagnetic radiation. They occupy a unique place within the electromagnetic spectrum. This spectrum includes everything from long radio waves to short gamma rays. Microwaves sit between ordinary radio waves and infrared light.

Their wavelengths are shorter than radio waves but longer than infrared waves. Typically, their wavelengths range from about one meter to one millimeter. This corresponds to frequencies between 300 MHz and 300 GHz. Because these waves are so small, the name "microwave" was chosen to indicate their size compared to earlier radio technology.

Understanding how microwaves move is essential for engineering. Unlike lower frequency radio waves, microwaves travel via line-of-sight paths. They do not diffract, which means they cannot bend around hills or obstacles. They also do not follow the Earth's surface as ground waves. Furthermore, they do not reflect off the ionosphere like skywaves do.

This means terrestrial communication links are limited by the visual horizon. On the Earth's surface, the range is limited to about 40 kilometers. At the highest frequencies, the atmosphere itself interferes with the signal. Gases in the air absorb the energy, which limits practical distances to around one kilometer.

Engineers categorize microwave frequencies into specific bands. These designations often use letters to identify different ranges. One common system is the IEEE radar band designations. These include the S, C, X, Ku, K, and Ka bands.

Another system used by the Radio Society of Great Britain (RSGB) provides even more detail. For example, the S band ranges from 2 to 4 GHz. This band is used for weather radar, Bluetooth, and Wi-Fi. The X band ranges from 8 to 12 GHz and is used for satellite communications. The Ku band covers 12 to 18 GHz, while the Ka band spans 26.5 to 40 GHz. These specific bands allow different technologies to work without interfering with one another.

History shows how our understanding of these bands has evolved. During World War 2, the U.S. used a top-secret classification system for radar bands. This became the foundation for the modern letter-based system. Scientists also discovered a problem while developing radar at the K band. They realized that water vapor and oxygen in the atmosphere absorb certain frequencies. To solve this, they split the original K band into two parts. They created the lower Ku band and the upper Ka band to avoid these atmospheric absorption issues.

Microwaves are used in a vast array of modern technologies. In your kitchen, a device called a magnetron generates waves to cook food.

In the world of telecommunications, they power satellite and spacecraft communication.

They are also vital for radar systems and wireless networks. Even medical science uses them for diathermy and cancer treatment. You might also encounter them in small consumer electronics. Garage door openers and keyless entry systems rely on these waves to function. They are even used in particle accelerators and radio astronomy to study the universe.

Because of their short wavelengths, microwave antennas can be very small. This is why your cell phone can have a tiny antenna inside it.

Portable devices often use small antennas like whip antennas or patch antennas. However, for long-distance communication, larger antennas are required. Parabolic "dish" antennas are the most common type used for directing beams.

These dishes can create narrow beams. Narrow beams are helpful because they do not interfere with nearby equipment. This allows engineers to reuse the same frequency in different locations.

Moving microwaves requires specialized hardware. At low frequencies, engineers use coaxial cables. However, at microwave frequencies, these cables lose too much power. Instead, engineers use metal pipes called waveguides to carry the signals.

In some high-frequency applications, the atmosphere becomes almost opaque. Above 100 GHz, the absorption by the atmosphere is so strong that signals cannot pass easily. This makes microwave technology a precise tool that must be carefully managed based on the environment and the specific frequency being used.