What are Microwaves? Everything You Need to Know

Electromagnetic spectrum

What are Microwaves? Everything You Need to Know

Were you aware that when you heat up your instant mashed potatoes in the microwave, you’re exposing them to microwave radiation? Okay, maybe you could have guessed by the name. However, this light energy can do much more than warm up your dinner in a pinch. 

From acoustic sonar profiling to background noise across the universe, microwave energy plays an important role in our lives. Continue reading for everything you need to know about this type of radiation and how we use it.

What Are Microwaves? Complete Explanation

Microwaves make up a portion of the electromagnetic spectrum, which transports light photons across space. This portion of the EM spectrum has a relatively long wavelength and low power. You’ll find microwaves following radio waves and preceding infrared radiation, with their wavelengths averaging the diameter of a baseball.

When studying light energy on the electromagnetic spectrum, scientists typically use one of three types of metrics: frequency (measured in hertz), wavelength (measured in meters), or energy (measured in electron volts). The metric used for each portion often depends on which one is easiest to use. Researchers typically measure microwaves in wavelengths or frequency. While there is no defining limit for each EM portion, they tend to range from 300MHz to 300GHz.

Discovered alongside radio waves in the late 1800s, the two electromagnetic portions share similar properties. Microwaves get their name for being the smallest-wave portion of the radio frequency. However, the two differ because microwaves don’t bounce on the ionosphere, making them less useful for communicating long distances.

However, this doesn’t mean they aren’t used for communicating at all; ultra-high frequency waves are useful for penetrating clouds, vapor, and even the atmosphere. This makes them ideal for communicating via satellite. Microwaves on the highest-frequency end of the portion also find uses in heating, such as with the microwave oven.

Microwaves: An Exact Definition

As the Food and Drug Administration defines them, “Microwaves are a form of electromagnetic radiation; they are waves of electrical and magnetic energy moving together through space.” This form of radiation makes up a portion of the entire electromagnetic spectrum.

The Encyclopedia Brittanica places the frequency of microwave radiation at 1 to 300GHz, corresponding with 30cm to 1mm wavelengths. This differs from NASA’s range of 300MHz to 300GHz because much of the microwave portion is considered part of the radio frequency.

For a more detailed breakdown of this form of radiation, the Institute of Electrical and Electronics Engineers (IEEE) developed specific designations for radar bands based on their uses.

Frequency DesignationFrequency Measurement
High Frequency (HF)3 – 30MHz
Very High Frequency (VHF)30 – 300MHz
Ultra High Frequency (UHF)300 – 1000MHz
L1 – 2GHz
S2 – 4GHz
C4 – 8GHz
X8 – 12GHz
Ku12 – 18GHz
K18 – 27GHz
Ka27 – 40GHz
V40 – 75GHz
W75 – 110GHz

Where Do Microwaves Come From?

James Webb telescope space image

As microwaves share much of the same range as radio waves, their natural sources are similar. When the magnetic fields between two objects collide, they create radio frequencies. The more massive the two objects, the more energy is released. The higher frequency range of these collisions is described as microwaves.

Due to their proximity to the infrared light portion, we start to see the beginnings of heat sources in the higher-frequency ranges of microwaves. As such, many celestial objects release a natural microwave frequency for simply existing. This discovery, called the cosmic microwave background, was a major step forward in understanding the electromagnetic spectrum.

How Do You Create Microwaves?

Despite their discovery in the late 1800s, microwaves were practically useless until nearly 1937. American engineers designed the klystron, a vacuum tube capable of amplifying radio frequencies. The tube accelerated electrons, which raised the frequency to the desired range based on application.

Another tool used to create microwaves is the magnetron. This piece of equipment directs electric current through oscillating cavities, which cause the electrons to get excited. Magnetrons can create quick bursts of high-frequency energy, making them ideal in radar systems and microwave ovens.

Who Discovered Microwaves?

Building on the theory put forward by James Clerk Maxwell, German physicist Heinrich Hertz discovered radio frequency in 1887. While experimenting with an induction coil and an improvised capacitor, Hertz created electromagnetic waves. He detected these waves using two electrodes separated by a small gap. While incredibly small, Hertz could see the waves as they passed through the gap. 

Despite his discovery, the physicist could not determine any use for radio frequency, particularly the higher-frequency range. It would take nearly 50 years for microwaves to find an application.

Cosmic Microwave Background

While the concept of microwaves had already been established, we significantly broadened our understanding of it in 1965. Arno Penzias and Robert Woodrow, two astronomers at Bell Telephone Laboratories, built a specialized horn antenna to study astronomical radio frequencies. The pair accidentally discovered a strange microwave frequency that permeated space from all directions and with little variance.

The background noise, called cosmic microwave background (CMB) radiation, is thought to be residual energy from the Big Bang, the theory of the universe’s beginning. CMB has led researchers to fantastic discoveries, including dark matter, galactic clusters, and possible events predating the universe’s existence. Penzias and Woodrow received the 1978 Nobel Prize for their discovery.

What Are the Applications of Microwaves?


Due to their short wavelength, microwaves are great telecommunication and broadcasting vehicles. The directional antennas are smaller than the ones needed to pass along low-frequency radio waves, making them more practical. Applications for microwaves in communication include Bluetooth, mobile broadband, and most satellite internet such as Starlink.


The FDA states that microwaves have the characteristics necessary for cooking; they reflect off the metal, pass through thin materials such as glass or paper, and are absorbed by food. With the development of affordable magnetrons, this type of radiation finds its most common use in microwave ovens. Other applications for heating include drying and curing industrial products and plasma generation. The U.S. Air Force has also implemented the wavelength into less-than-lethal weaponry for riot control.


James Webb in outer space on Earth's orbit
James Webb Space Telescope use high infrared resolution to capture distant objects in space.

In addition to studying the CMB, researchers use microwaves to study many low-energy celestial bodies. In particular, astronomers at NASA have used radio telescopes to bounce this frequency off planets in our solar system. These experiments have helped us determine the distance to our moon as well as the location of Venus. Scientists also use microwaves to analyze stars, galaxies, and nebulas. 

Examples of Microwaves in the Real World

The Doppler Effect

In 1842, Austrian physicist Christian Doppler discovered that wave frequencies change as the source moves. This effect, named the Doppler effect, found application in discovering the location of objects in the water in relation to a resonator. This tool, called an acoustic Doppler current profiler, is the primary tool of oceanographers studying water velocity as affected by current.

Microwave Ovens

Following WWII, electronics specialist Percy L. Spencer discovered, while standing next to a large magnetron at a Raytheon laboratory, that radiant energy melted a candy bar in his pocket. This led to the experimentation of microwave ovens using personal-sized magnetrons. While originally too large for consumer use, the technology is now found in nearly every household in the United States.

Atacama Large Millimeter and Submillimeter Array

Due to the interference of the atmosphere, astronomers can only study a small portion of the microwave frequency from the Earth’s surface. The largest terrestrial observatories are the Atacama Large Millimeter and Submillimeter Array (ALMA) in northern Chile. Located at 16,000 feet elevation, ALMA uses 66 large radio telescopes for interferometry of low-frequency radiation. The array began observation in 2011 and provided insights into several comets, planetary formations, and black holes.

Microwaves: Further Reading

Whether it’s heating your food or understanding the universe’s birth, microwaves play an important role in our lives. This form of radiation makes up just one portion of the electromagnetic spectrum. For more on how we use EM radiation every day, check out the articles below.

Frequently Asked Questions

How do microwaves compare to radio waves?

Sharing similar frequencies, microwaves and radio waves have a lot in common. However, where radio waves bounce off the ionosphere, microwaves do not. This makes them less useful for certain types of communication. However, radio waves have a unique characteristic of traveling through vapor, making them great for satellite communication. Additionally, microwaves begin to produce heat at the high-frequency end of their range, allowing them to warm objects in certain applications.

Where are microwaves found on the electromagnetic spectrum?

Microwaves are found between radio waves and infrared light on the electromagnetic spectrum. They share characteristics with both portions, making great frequencies for telecommunication as well as heating objects.

How are microwaves produced on the electromagnetic spectrum?

Similar to radio waves, microwaves are produced when the magnetic fields of two objects collide. More massive objects have the potential to produce higher frequency waves, which enter the microwave region.

What frequency are microwave ovens?

Microwave ovens typically run on the S-band of the microwave portion, which ranges from about 2 to 4GHz. Most conventional ovens have a standard frequency of 2.45GHz.

How are microwaves typically used?

Microwaves have a wide range of applications, which include communication, navigation, radar, heating, and spectroscopy. Common uses include Bluetooth technology, microwave ovens, air traffic control, and speed limit enforcement.

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