This article will go over the basic fundamentals of RF theory. Information will be provided in an easy-to-understand manner to ensure even the most clueless PFC has a solid grasp on the subject.

First things first: What is a radio wave?

A radio wave is any electromagnetic (EM) wave that falls within the frequency range of 3 kHz to 300 GHz in the electromagnetic spectrum.

As you can see, visible light is also part of the EM spectrum.

Waves in the EM spectrum interact with the world differently depending on what part of the spectrum they reside in.

How do we describe radio waves?

Radio waves have a few basic metrics we can use to describe them, some of the most important ones include:

Wavelength- Wavelength is the distance between two consecutive peaks or troughs of a wave, showing how long one cycle of the wave is. Wavelength can be as physically tall as a US state, or as small as a millimeter (or smaller). Wavelength plays a major role in how radio waves will interact with objects in the physical world.

Frequency- Frequency is the number of times a wave completes a full cycle in one second, measured in hertz (Hz).

Amplitude- Amplitude is the height of a wave from its midpoint to its peak or trough, representing the wave's strength or intensity.

Phase-The phase of a wave refers to its position within a single cycle of its oscillation, usually measured in degrees.

This graphic visually depicts frequency and wavelength. Amplitude can be thought of as how tall these waves are.

This graphic shows the different positions a wave can be in within its cycle and their respective phase, measured in degrees from 0-360

How do we differentiate between different parts of the RF spectrum?

In the business, we usually just refer to portions of the spectrum itself. The main ones EW operators would care about are as follows:

High Frequency- 3-30Mhz

Very High Frequency- 30-300Mhz

Ultra High Frequency- 300Mhz-3Ghz

Super High Frequency- 3Ghz-30Ghz

What are each of these generally used for?

High Frequency- Long-distance communication, especially for radio broadcasting, aviation, and military communication.

Very High Frequency- Local and regional communication. TV broadcasts, FM radio, marine communication, and emergency services.

Ultra High Frequency- Short-range communication, such as mobile phones, Wi-Fi, and GPS.

Super High Frequency- High-speed communication and radar systems. Satellite communication, microwave links, and weather radar.

Lets talk about radio wave propagation i.e. how radio waves move.

As we talked about before, radio waves interact with the world differently based on factors like what part of the spectrum they reside in. Radio waves can interact with the environment in interesting ways, lets define some of those ways then show a few graphics:

Refraction: The bending of a radio wave as it passes through different media, typically caused by changes in the wave’s speed.

Diffraction: The bending of radio waves around obstacles or through openings, causing them to spread out.

Multipath: A phenomenon where a radio signal arrives at the receiver via multiple paths due to reflections, diffractions, or scattering.

Reflection: The bouncing of radio waves off surfaces, such as buildings or mountains, that causes a change in direction.

Here is a few more terms you should know:

Absorption: The process by which a medium absorbs radio waves, converting the signal into heat and reducing the wave’s strength.

Scattering: The redirection of radio waves in multiple directions when they encounter irregularities in the medium, like raindrops or buildings.

Polarization: The orientation of the electric field of a radio wave, which can be either vertical, horizontal, or circular.

Attenuation: The reduction in the strength of a radio signal as it travels through a medium, typically due to distance or obstacles.

Interference: The overlap of two or more radio signals that disrupts the clarity or strength of a communication signal.

Doppler Effect: A shift in the frequency of a radio wave due to the relative motion between the transmitter and receiver.

Now, lets discuss how we can use these radio wave properties to our advantage:

Skywave communications- A type of radio wave propagation where the wave travels from the transmitter, reflects off the ionosphere, and returns to Earth, enabling long-distance communication.

Groundwave communications- A radio wave that follows the Earth's surface, typically used for short-range communication.

Line of sight- A type of communication where the transmitter and receiver must be within “direct view” of each other, with no major obstructions between them, allowing for clear signal transmission

Next up: The Importance of Amplitude and Power

Amplitude directly impacts the power of a radio wave. In simple terms, higher amplitude means higher power, which means a stronger signal. A stronger signal can travel farther, overcome obstacles more effectively, and improve the clarity of the transmission.

In communication systems and broadcasting, adjusting the amplitude (and thus the power) is key to ensuring signals reach the intended distance and are actually received. More power can also help with signal penetration in bad communications environments, like urban areas with many obstructions.

Lets talk antennas

Antenna- An antenna is a device that transmits or receives radio waves by converting electrical signals into electromagnetic waves (and vice versa) in the radio frequency spectrum.

Antenna Size and Transmission Properties- The size of an antenna is closely tied to the wavelength of the signal it is designed to handle. Generally, for efficient transmission and reception, an antenna's size needs to be a fraction of the wavelength of the frequency it operates on.

Resonance: An antenna is most efficient when its length is related to the wavelength of the frequency, typically a half or quarter wavelength. For example, for a signal at 100 MHz (which has a wavelength of about 3 meters), a half-wave dipole antenna would be around 1.5 meters long.
Frequency Range: Larger antennas typically work better at lower frequencies (longer wavelengths), while smaller antennas are better for higher frequencies (shorter wavelengths). As the frequency increases, the antenna size decreases.
Gain and Directivity: A larger antenna, such as a parabolic dish, often has higher gain and more focused directionality. This means it can transmit more power in a specific direction, increasing signal strength over longer distances.

Lastly for our 101 article, lets discuss some of the different antenna types

Omnidirectional Antenna– Radiates equally in all directions, used for general communication (like vertical whip antennas).

Directional Antenna– Focuses energy in a specific direction to increase range and reduce interference (Yagi, parabolic dish).

Yagi-Uda Antenna– A high-gain directional antenna used for long-range communication, TV reception, and ham radio.

Dipole Antenna– A basic and widely used antenna with moderate gain, used in HF/VHF/UHF communications.

Parabolic Dish Antenna– A high-gain antenna that uses a curved reflector, used for satellite communications and radar.

Longwire Antenna– A simple wire antenna used for HF communications, especially for long-distance (skywave) propagation.

Loop Antenna– A compact, efficient antenna used in direction-finding (DF) and certain HF applications.

Patch (Microstrip) Antenna– A low-profile, directional antenna used in mobile and satellite applications (e.g., GPS).

Phased Array Antenna– Uses multiple elements to steer the signal electronically without moving parts, used in radar and military applications.

DF (Direction-Finding) Antenna– Used to locate signal sources, often found in military, intelligence, and search-and-rescue operations.

Now wasn’t that riveting? If you’d like to learn more about RF theory, check out the “RF Theory 102” article where we dive into the various modulation types

Most images courtesy of wikimedia commons:

https://commons.wikimedia.org/wiki/File:Refraction_effects_pencil_appears_broken_in_water.jpg

https://commons.wikimedia.org/wiki/File:Water_ripples_Diffraction.png

https://commons.wikimedia.org/wiki/File:Gps-multipath-efect.png

https://commons.wikimedia.org/wiki/File:Skywave_groundwave.png

RF Theory 101