Radiated energy refers to electromagnetic energy that is transmitted through space in the form of electromagnetic waves. This energy propagates through free space at the speed of light and can carry information over long distances. The main principles behind radiated energy are:

– Electromagnetic radiation: Radiated energy takes the form of electromagnetic waves generated by oscillating electric and magnetic fields. These waves have electrical and magnetic field components that propagate perpendicularly to each other.

– Transmission and reception: Energy is radiated from a transmitting antenna, propagates through space, and is captured by a receiving antenna. The transmitting and receiving antennas must be tuned to the same frequency.

– Modulation: Information can be encoded onto a radio wave by modulating properties like its amplitude, frequency, or phase. The receiver can then extract the information.

– Propagation: Radio waves can propagate through different mediums like air, vacuum, or water. The medium impacts the speed and manner of propagation.

– Frequency bands: Radiated energy utilizes different frequency bands like radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays. Different bands have distinct properties.

Electromagnetic radiation refers to energy that travels in waves and spans a spectrum from very long radio waves to very short gamma rays. This radiation carries energy through oscillating electric and magnetic fields, and it does not require a medium like air or water to travel through. The key properties of electromagnetic waves include:

• Frequency – The number of wave oscillations that pass a point per second, measured in Hertz (Hz). Higher frequency equals shorter wavelength.
• Wavelength – The distance between consecutive wave peaks, which determines how tightly the waves are packed. Shorter wavelength means higher frequency.
• Amplitude – The height or intensity of the wave from peak to trough.
• Speed – All electromagnetic waves travel at the speed of light in a vacuum, approximately 3 x 10^8 meters per second.

The electromagnetic spectrum categorizes radiation by frequency and wavelength, with the entire range of possible frequencies extending from below one hertz to above 10^25 hertz. From lowest to highest frequency, the spectrum comprises:

• Microwaves
• Visible light
• Ultraviolet rays
• X-rays
• Gamma rays

Different types of electromagnetic radiation have diverse applications across science, technology, medicine, communications, and more. But all exhibit the underlying wave-like characteristics of frequency, wavelength, amplitude, and speed.

Antennas

The purpose of antennas in radiated energy systems is to efficiently convert signals in transmission lines into electromagnetic waves that can propagate through space, and vice versa. Antennas essentially act as the interface between guided waves (in transmission lines) and free space propagating waves.

There are many different types of antennas that serve different purposes. Some key types include:

• Dipole antennas – these are simple linear antennas that are commonly used. They consist of two metal rods or wires oriented end to end, with a small feed gap between them.
• Monopole antennas – these consist of a single metal rod or wire mounted above a ground plane. The ground plane acts like a mirror to create the effect of a dipole antenna.
• Loop antennas – these are antennas formed into a loop shape. They are commonly used for receiving signals.
• Aperture antennas – these use horn or reflector dishes to focus radiated energy into a beam. They provide high gain and directivity.
• Array antennas – these consist of multiple antenna elements working together. This allows steering and shaping of radiation patterns.

Antennas can also have different directional radiation patterns. Omnidirectional antennas radiate energy equally in all directions on one plane. Directional antennas focus energy into a beam pointed in a specific direction. Highly directional antennas are used for long-distance communications.

Propagation

Radiated energy travels in the form of electromagnetic waves. The propagation of these waves depends on the frequency, antenna properties, and characteristics of the transmission medium. There are different propagation mechanisms:

Ground waves – These travel along the surface of the earth, following the curvature of the earth. They are composed of a direct wave and a ground reflected wave. Ground waves are used by AM radio stations. Lower frequency signals like AM radio can travel longer distances using ground waves.

Sky waves – At higher frequencies, radiated waves travel upward and are reflected back down by the ionosphere. This allows signals to travel beyond the horizon. The refraction in the ionosphere enables shortwave and HF signals to travel very long distances around the world.

Scattering – Rough terrains, buildings, foliage, lamp posts etc. can cause scattering, reflection and diffraction of radiated waves, altering their path. The scattered waves arrive at the receiver from different angles.

Modulation

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. The three key types of modulation are:

Amplitude Modulation (AM)

AM varies the amplitude (strength) of the carrier signal in proportion to the amplitude of the modulating signal. For example, voice signals at audible frequencies can modulate an AM transmission.

Frequency Modulation (FM)

FM varies the frequency of the carrier signal proportional to the amplitude of the modulating signal. FM is less susceptible to noise and interference than AM. FM is commonly used for high-fidelity radio and television audio broadcasts.

Phase Modulation (PM)

PM varies the phase of the carrier signal proportional to the amplitude of the modulating signal. This represents information as variations in the instantaneous phase of the carrier wave. PM is widely used for wireless and optical communications.

Encoding

Digital data is encoded before it can be transmitted as radiated energy. There are several common encoding methods used:

• Amplitude Shift Keying (ASK) – The amplitude of the signal is varied to represent binary 1s and 0s.

• Frequency Shift Keying (FSK) – The frequency of the signal is shifted between two frequencies to represent binary 1s and 0s.

• Phase Shift Keying (PSK) – The phase of the signal is shifted to represent binary data. Binary phase-shift keying (BPSK) uses two phases separated by 180 degrees.

• Quadrature Amplitude Modulation (QAM) – Both amplitude and phase are modulated to represent digital data. 16-QAM and 64-QAM are commonly used in technologies like WiFi.

These encoding methods allow digital data such as text, images, video, and audio to be represented as a radio signal that can be transmitted wirelessly.

Transmission Medium

The transmission medium is what carries the radiated electromagnetic energy from the transmitting antenna to the receiving antenna. There are different types of transmission mediums that each have their advantages and disadvantages:

Air and Outer Space: Air and outer space allow electromagnetic waves to travel freely without obstructions. Broadcast TV and radio use the air as their transmission medium to reach receiving antennas. Satellites in space also use the vacuum of space to transmit signals over very long distances. The downside is that air and space can be affected by weather and other interference.

Water: Water allows the propagation of electromagnetic waves, which is why sonar and underwater communications are possible. But water attenuates and absorbs electromagnetic energy more than air. The conductivity of water also affects the propagation of signals.

Fiber Optics: Fiber optic cables use glass or plastic fibers to transmit light signals. This allows for extremely high bandwidth communications over long distances with low attenuation compared to copper cable. Fiber optics are ideal for high-speed internet, computer networks, and telecommunications. But they require more complex transmitters/receivers and installation.

Reception

Receiving antennas play a key role in capturing radiated energy and converting it into electrical signals that can be processed. They are designed to efficiently pick up the radio waves being transmitted and feed them into the receiver circuitry. The most common types of receiving antennas are:

• Dipole antennas – Two conductive elements connected to a receiver, capable of picking up signals across a wide frequency range. They are low cost and simple to construct.
• Loop antennas – A loop or coil of wire that picks up magnetic field components of radio waves. They are compact and good for AM radio reception.
• Parabolic antennas – Dish shaped antennas that focus radio waves onto a receiver. They provide high gain and directivity.
• Horn antennas – Flared metal waveguides that collect and concentrate radio waves. Used for microwave links and satellite dishes.

The antenna feeds the weak received signal into the input stage of a radio receiver. This low noise amplifier boosts the signal strength while adding minimal noise. The signal then passes through circuitry that demodulates it, extracting the information bearing modulation from the carrier wave.

For analog modulation like AM and FM radio, demodulation circuits recover the audio signal. AM detection can be done using diode detectors, while FM detection requires additional components like a discriminator. With digital modulation, the receiver first demodulates then decodes the signal to recover the original binary data. Decoding may involve bit synchronizers, deinterleavers, error correction, and other techniques to reconstitute the data stream.

The end result is information recovery. Radiated signals encoding audio, video, data or other content get converted back to their original forms by the receive chain.

Applications

Radiated energy has enabled many key technologies that have transformed modern life:

Radio broadcasting uses electromagnetic waves to transmit audio from a broadcasting antenna to home and car radios. Radio waves are modulated and encoded with information that is decoded by radios to play sound. Radio enabled the first mass communication medium.

Television

Television expanded upon radio technology by adding video transmission through encoding both visual and audio data on radio waves. Broadcast towers transmit television signals that are picked up by antennas and displayed on television sets. Television revolutionized entertainment and news.

Radar uses radiated electromagnetic waves to detect the position and speed of objects like aircraft and ships. It works by transmitting radio waves that bounce off targets and reflect back to the radar antenna. Radar is used for applications like weather tracking, speed guns, and guided missiles.

Cell Phones

Cellular networks allow mobile phones to connect wirelessly using radio waves. Cell towers have service areas where they send and receive signals from cellular devices like mobile phones and tablets. This enables wireless communication from nearly anywhere a user can connect to a cellular network.

Conclusion

In summary, radiated energy involves transforming information into electromagnetic signals that can propagate through space to convey information. It begins with encoding data into a modulated carrier wave using an antenna to radiate the signal. The radio waves then propagate according to the laws of physics, interacting with the environment and spreading out over distance. With the right antenna and receiver, the signal can be captured and decoded to recover the original information.

Looking to the future, radiated energy technologies will continue advancing hand-in-hand with communication systems. Faster data rates, lower latencies, and increased reliability will open up new applications. Research into novel modulation schemes, metamaterials, and phased array antennas will push performance boundaries further. The ubiquity and importance of wireless communications ensures that radiated energy will remain a vibrant field of research and development for decades to come.