Directional Antennas

It has already been mentioned that ideal omnidirectional antennas cannot be produced in reality. Nonetheless only antennas that focus their radiated power in a particular spatial direction can properly be called directional antennas. At an equivalent transmit power, they significantly improve the signal-to-noise ratio, but must be aligned on the distant station so that in many cases a rotation facility has to be used. For directional antennas the parameters gain, directivity and all values associated with the radiation pattern, like front-to-back ratio, side-lobe suppression or half-power beamwidth as already discussed give an overview about how much the radiated energy is focused into a certain direction. The simplest form of a directional antenna is a setup of two monopole antennas at a predefined distance, which are fed with different phase

Principle of a directional antenna

In the example a distance of a quarter wavelength and a phase difference of 90° have been chosen, resulting in a cardioid shaped radiation pattern when the far field strengths generated by the two individual antennas are added.

Cardiold shape radiation pattern

Even though this configuration does not produce strongly focused radiation, it however exhibits a sharply defined null towards the backside which can effectively be used to suppress interfering signals. By superimposing the diagrams obtained by combining two or several radiators arranged at defined distances and with defined phase shifts, directional patterns can be generated whose directivity is limited mainly by the available space to setup the number of required radiators. Instead of feeding the radiators via cables , the principle of radiation coupling is mostly applied in practice, with only one radiator being fed from the cable and the remaining elements activated by this radiator. Yagi-Uda antennas, which are commonly used for the reception of TV and VHF sound broadcast signals, have typically between 4 and 30 elements and yield gain values of 10 dB and more. The possibility of changing the direction of the main beam of a highly directive antenna by purely electronic means is utilized to an increasing extent also with antenna arrays for very high frequencies (e.g. for satellite radio services). The antennas used are referred to as planar antennas and mostly consist of a dipole curtain which, in contrast to curtain antennas, is installed in front of a conductive plane. This array can also be implemented by etching the radiators as tracks into a printed circuit board (microstrip antenna). In this way, even large arrays of antennas can be implemented for the microwave frequency range with high precision and efficiency.

=* by Rohde & Schwarz*=

How does a whole house surge protector work ?

What is a surge voltage ? How does it occur ?

Various types of surge voltages occur in electrical plants and electronic systems. They are differentiated mainly by their duration and power. Depending on the cause, a surge voltage can last a few hundred microseconds, hours or even days. The amplitude can range from a few millivolts to some ten thousand volts. The direct or indirect consequences of lightning strikes are one particular cause of surge voltages. Here, during the surge voltage, high surge currents with amplitudes of up to some ten thousand amperes can occur. In this case, the consequences are particularly serious. This is because the damaging effect first of all depends on the power of the respective surge voltage pulse.

The phenomenon of surge voltage 

Every electrical device has a specific dielectric strength. If the level of a surge voltage exceeds this strength, malfunctions or damage can occur. Surge voltages in the high or kilovolt range are generally transient overvoltages of comparatively short duration. They generally last from a few hundred microseconds to a few milliseconds. As the maximum amplitude of such transients can amount to several kilovolts, steep voltage increases and differences are often the consequence. Surge protection is the only thing that helps. Indeed, the operator of an electrical system generally replaces the material damage to the system with corresponding protection. However, the difference in time between failure of the system to maintenance represents a risk in itself. This failure is often not covered by insurance and, within a short period of time, can become a heavy financial burden – especially in comparison to the cost of a lightning and surge protection concept.

This is how surge protection works

Surge protection should ensure that surge voltages cannot cause damage to installations, equipment or end devices. As such, surge protective devices (SPDs) chiefly fulfil two tasks: • Limit the surge voltage in terms of amplitude so that the dielectric strength of the device is not exceeded. • Discharge the surge currents associated with surge voltages. The way in which the surge protection works can be easily explained by means of the equipment's power supply diagram (Fig. 7). As described in Section 1.4, a surge voltage can arise either between the active conductors as normalmode voltage (Fig. 8) or between active conductors and the protective conductor or ground potential as common mode voltage (Fig. 9).

With this in mind, surge protective devices are installed either in parallel to the equipment, between the active conductors themselves (Fig. 10) or between the active conductors and the protective conductor (Fig. 11). A surge protective device functions in the same way as a switch that turns off the surge voltage for a brief time. By doing so, a sort of short circuit occurs; surge currents can flow to ground or to the supply network. The voltage difference is thereby restricted (Fig. 12 and 13). This short circuit of sorts only lasts for the duration of the surge voltage event, typically a few microseconds. The equipment to be protected is thereby safeguarded and continues to work unaffected.

Lightning and surge protection standards 

National and international standards provide a guide to establishing a lightning and surge protection concept as well as the design of the individual protective devices. A distinction is made between the following protective measures: • Protective measures against lightning strike events: lightning protection standard IEC 62305 deals with this. A key component of this is an extensive risk assessment regarding the requirement, scope, and cost-effectiveness of a protection concept. • Protective measures against atmospheric influences or switching operations: IEC 60364-4-44 deals with this. In comparison with IEC 62305, it is based on a shortened risk analysis and uses this as the basis for deriving corresponding measures. In addition to the standards mentioned, if applicable, other legal and country- specific stipulations are also to be considered.

What is the basic principle of antenna?

An antenna is defined by Webster‘s Dictionary as ―a usually metallic device (as a rod or wire) for radiating or receiving radio waves.‖ The IEEE Standard Definitions of Terms for Antennas (IEEE Std 145–1983) defines the antenna or aerial as ―a means for radiating or receiving radio waves.‖ In other words the antenna is the transitional structure between free-space and a guiding device. The guiding device or transmission line may take the form of a coaxial line or a hollow pipe (waveguide), and it is used to transport electromagnetic energy from the transmitting source to the antenna or from the antenna to the receiver. In the former case, we have a transmitting antenna and in the latter a receiving antenna.

An antenna is basically a transducer. It converts radio frequency (RF) signal into an electromagnetic (EM) wave of the same frequency. It forms a part of transmitter as well as the receiver circuits. Its equivalent circuit is characterized by the presence of resistance, inductance, and capacitance. The current produces a magnetic field and a charge produces an electrostatic field. These two in turn create an induction field. 

Definition of antenna 

An antenna can be defined in the following different ways: 

1. An antenna may be a piece of conducting material in the form of a wire, rod or any other shape with excitation. 

2. An antenna is a source or radiator of electromagnetic waves. 

3. An antenna is a sensor of electromagnetic waves. 

4. An antenna is a transducer. 

5. An antenna is an impedance matching device. 

6. An antenna is a coupler between a generator and space or vice-versa.

source : https://www.sathyabama.ac.in/sites/default/files/course-material/2020-10/SEC1301.pdf

Electromagnetic Radiation

Electromagnetic Radiation is energy in the form of a wave of oscillating electric and magnetic fields, the wave travels through a vacuum at a velocity of 2.998 x 10^8 meters per second (186,284 miles per second). The Wavelength of an electromagnetic wave determines its properties , x-rays , infrared , microwaves , radio waves and light are electromagnetic radiation. 

                                                             WAVELENGTH

Electromagnetic radiation (EMR) is a form of energy that surrounds us in various forms and has profound effects on our daily lives, scientific research, and technological advancements. It is energy that travels and spreads out as it moves—taking the form of visible light, radio waves, microwaves, X-rays, and other wavelengths on the electromagnetic spectrum. In this article, we’ll delve deep into what electromagnetic radiation is, how it works, its different types, and its applications and impacts on human life.

What Is Electromagnetic Radiation?

Electromagnetic radiation is composed of electric and magnetic fields that oscillate perpendicular to each other and the direction of the energy's travel. This dual-wave nature allows EMR to move through the vacuum of space as well as through various materials. Unlike sound, which needs a medium (like air or water) to travel through, EMR can move through empty space.

The Nature of Electromagnetic Waves

Electromagnetic radiation has both particle-like and wave-like properties, a duality explained by quantum mechanics. Each particle of electromagnetic radiation is known as a photon, which travels at the speed of light (approximately 299,792 kilometers per second in a vacuum). Photons have no mass but possess energy and momentum, which makes them unique. The amount of energy they carry depends on their frequency—the higher the frequency, the more energy each photon carries.

The Electromagnetic Spectrum

The electromagnetic spectrum encompasses all types of electromagnetic radiation. The spectrum is typically divided into seven major categories based on wavelength and frequency:

1. Radio Waves (low frequency, long wavelength): Used in communication systems such as radios, televisions, and cell phones.

2. Microwaves: Employed in microwave ovens, radar, and satellite communications.

3. **Infrared Radiation**: Used in night vision equipment, remote controls, and thermal imaging.

4. **Visible Light**: The only part of the spectrum visible to the human eye, encompassing all colors from violet to red.

5. **Ultraviolet (UV) Radiation**: Naturally emitted by the sun, can cause skin burns and is used in sterilization.

6. **X-Rays**: Commonly used in medical imaging to view bones and other structures inside the body.

7. **Gamma Rays**: Extremely high-energy waves produced by radioactive atoms and certain astronomical processes, used in cancer treatment and scientific research.

Each type of radiation on the spectrum has distinct applications, properties, and effects.

Properties of Electromagnetic Radiation

The characteristics of electromagnetic radiation include its **wavelength**, **frequency**, and **speed**.

- **Wavelength** is the distance between two peaks (or troughs) of a wave. The longer the wavelength, the lower the frequency.

- **Frequency** is the number of wave cycles per second, measured in hertz (Hz). High-frequency waves carry more energy.

- **Speed** of EMR in a vacuum is constant at approximately 300,000 kilometers per second, though it can slow down when passing through different media like glass or water.

How Electromagnetic Radiation Works

The behavior of electromagnetic radiation can vary depending on its wavelength and the type of material it encounters. EMR can be **reflected**, **refracted**, **absorbed**, or **scattered**.

- **Reflection** occurs when EMR bounces off surfaces, like light reflecting from a mirror.

- **Refraction** happens when EMR passes through a medium and changes direction, which is why objects look distorted when viewed through water.

- **Absorption** is when a material takes in the energy of the EMR, as seen when sunlight warms the skin.

- **Scattering** occurs when EMR is forced to deviate from its straight path, often by particles in the atmosphere.

### Applications of Electromagnetic Radiation

Electromagnetic radiation is indispensable in both science and technology. Here’s a closer look at some of its uses:

#### Communication

Electromagnetic radiation, particularly in the radio and microwave parts of the spectrum, is essential in communication. Radio waves transmit audio, television, and data signals. Microwaves are used in mobile networks, Wi-Fi, and satellite communications.

#### Medicine

In the medical field, X-rays are pivotal in imaging bones and tissues, while gamma rays are used in radiotherapy for cancer treatment. UV radiation can also be used to sterilize medical equipment. Infrared technology aids in heat-based therapies and infrared saunas.

#### Industry

EMR finds widespread industrial applications. For instance, infrared waves are used in thermal cameras to detect heat leaks and insulation issues. UV radiation is used in curing adhesives and coatings in manufacturing processes, while lasers (highly focused EMR) are used in cutting and welding metals.

#### Astronomy and Space Exploration

Astronomers rely on EMR to study distant galaxies, stars, and other celestial bodies. Different types of radiation, from radio waves to gamma rays, provide insights into the universe’s structure, formation, and evolution.

#### Everyday Devices

Our daily lives are filled with devices that rely on EMR. Microwaves cook food, remote controls operate TVs using infrared signals, and smartphones and laptops communicate via Wi-Fi signals. Even visible light—the lightbulbs in our homes—are forms of electromagnetic radiation.

### Effects of Electromagnetic Radiation on Health

Electromagnetic radiation’s effects on human health depend on the radiation type, intensity, and duration of exposure.

#### Non-Ionizing Radiation

Radio waves, microwaves, and visible light fall under **non-ionizing radiation**, meaning they don’t have enough energy to remove tightly bound electrons from atoms. This type of radiation is generally considered safe in low doses. However, prolonged exposure, especially to high levels of microwave radiation, can cause heating effects and potential tissue damage, which is why microwave ovens have shielding.

#### Ionizing Radiation

Ultraviolet rays, X-rays, and gamma rays are forms of **ionizing radiation**. This radiation has enough energy to ionize atoms and molecules, potentially damaging DNA and causing mutations. Prolonged exposure to ionizing radiation can lead to serious health issues like cancer. For instance, excessive exposure to UV radiation from the sun can cause skin cancer, which is why sunscreen is recommended.

Medical imaging procedures that use X-rays are generally safe due to the controlled doses, but frequent or prolonged exposure should be avoided.

### Safety and Protective Measures

Given the potential hazards of electromagnetic radiation, several safety guidelines and protective measures are in place:

- **Limit exposure to high levels of EMR**: Medical professionals take precautions during X-ray procedures, such as using lead shields to protect patients and personnel.

- **UV Protection**: Applying sunscreen, wearing sunglasses, and limiting direct sun exposure can protect against UV radiation.

- **Microwave Oven Safety**: Microwaves are designed with shielding to contain radiation. It’s advisable to avoid standing directly in front of a microwave while it's operating.

- **Safe Distance from EMR Sources**: Avoid prolonged use of cell phones and keep devices at a distance during sleep.

- **Regulations and Standards**: Regulatory bodies such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP) set limits for EMR exposure, especially for workers in industries where EMR exposure is a risk.

### Future Developments in Electromagnetic Radiation Research

As technology evolves, the study of electromagnetic radiation continues to advance. Scientists are exploring new ways to harness EMR safely and efficiently in fields such as:

- **Quantum Computing**: Quantum computers rely on the properties of EMR to manipulate quantum bits (qubits) and perform complex calculations.

- **Advanced Imaging Techniques**: Researchers are developing methods to use EMR more effectively in imaging technologies, allowing for non-invasive diagnostics and early disease detection.

- **Green Energy Solutions**: Solar power, which harnesses EMR from the sun, is becoming an increasingly popular and sustainable energy source.

- **Wireless Power Transmission**: Electromagnetic radiation is being studied for its potential to wirelessly transmit power, eliminating the need for wires and enabling more versatile power solutions.

### Conclusion

Electromagnetic radiation is one of the most critical forces in our universe, playing a significant role in natural phenomena and technological advances. From visible light that allows us to see to radio waves that enable global communication, EMR affects virtually every aspect of modern life. While certain types of EMR, like gamma rays and X-rays, require careful handling to prevent harm, others are indispensable in healthcare, communication, and entertainment.

Understanding EMR and its applications, alongside the potential health risks, is essential in a world increasingly reliant on electronic devices and communication networks. With ongoing research and evolving safety standards, the future holds promising possibilities for harnessing electromagnetic radiation safely, efficiently, and innovatively.

--- 

This should give you a good foundation on electromagnetic radiation. For specific subtopics or additional details, feel free to ask!

Electromagnetic Spectrum

nm = nanometer  ( 1 nm = 0.000000001 meter)

u    = micrometer ( 1 u    = 0.000001 meter)

mm= millimeter    ( 1 mm= 0.001 meter)

m   = meter          ( 1 m   = 39.37 inches)

km = kilometer     ( 1 km = 1000 meters)

Receiver for Fiber-Optic IR Extender

There are various types of remote-control extenders. Many of them use an electrical or electromagnetic link to carry the signal from one room to the next. Here we use a fibre-optic cable. The advantage of this is that the thin fibre-optic cable is easier to hide than a 75-Q coaxial cable, for example. An optical link also does not generate any additional radiation or broadcast interference signals to the surroundings. We use Toslink modules for connecting the receiver to the transmitter. This is not the cheapest solution, but it does keep everything compact. You can use a few metres of inexpensive plastic fibreoptic cable, instead of standard optical cable for interconnecting digital audio equipment. The circuit has been tested using ten metres of inexpensive plastic fibre-optic cable between the receiver and the transmitter (which is described elsewhere in this issue).

The circuit is simplicity itself. A standard IR receiver/demodulator (IC1, an SFH506) directly drives the Toslink transmitter IC2. We have used the RC5 frequency of 36 kHz, but other standards and frequencies could also be used. Both ICs are well decoupled, in order to keep the interference to the receiver as low as possible. Since the Toslink transmitter draws a fairly large current (around 20 mA), a small mains adapter should be used as the power source. There is a small printed circuit board layout for this circuit, which includes a standard 5-V supply with reverse polarity protection (D2). LED Dl is the power-on indicator. The supply voltage may lie between 9 and 30 V. In the absence of an IR signal, the output of IC1 is always High, and the LED in IC2 is always on. This makes it easy for the transmitter unit to detect whether the receiver unit is switched on. The PCB shown here is unfortunately not available readymade through the Publishers' Readers Services.

source : https://archive.org/details/ElektorCircuitCollections20002014/page/n13/mode/2up?view=theater