Radiating Success: A Guide to Antenna Theory and Design
“The laws of electromagnetism are the laws of the universe, and they apply not just to electromagnetic phenomena, but to everything in the universe.” — James Clerk Maxwell
Introduction
Antenna theory and design are crucial components in the field of wireless communication and technology. Antennas are responsible for transmitting and receiving radio signals, making them an integral part of devices such as radios, televisions, cell phones, and satellites. Understanding the basic principles of antenna theory and design can help improve signal quality and overall communication efficiency. In this blog, we will dive into the fundamentals of antenna theory and design, covering topics such as types of antennas, their characteristics, and design considerations. Whether you’re a student, hobbyist, or professional, this guide will provide you with a solid foundation in antenna theory and design.
In this post, We’ll be covering the following topics:
- Types of antennas and their applications
- Basic antenna parameters to consider
- Tools and software to get started
This post contains a lot of theory, and it’s easy to get bored and just drop the whole idea, but a little walk outside your comfort zone can really go a long way.
Right, let's get into it.
Types of Antennas
Antennas come in various shapes, sizes, and designs to suit different applications and frequency ranges. Some of the common types of antennas include directional antennas, omnidirectional antennas, patch antennas, Yagi antennas, and dish antennas. Directional antennas, such as Yagi antennas, have a focused beam and are ideal for long-range communication. Omnidirectional antennas, on the other hand, have a 360-degree coverage pattern and are used for short-range communication. Patch antennas are flat and rectangular and are widely used in wireless local area networks (WLANs). Dish antennas, also known as parabolic antennas, have a dish-shaped reflector and are used for satellite communication. Each type of antenna has its unique advantages and disadvantages, and the choice of the antenna depends on the specific communication requirements and frequency range. Let’s look at some examples
Dipole Antenna
Dipole antennas, also known as half-wave antennas, are one of the simplest and most widely used antennas in the world of wireless communication. They consist of two metal rods of equal length that are perpendicular to a conductor and are fed with an electrical current. Dipole antennas have a symmetrical omnidirectional radiation pattern and are typically resonant at their centre frequency. This means that they have maximum efficiency at the designed frequency, which makes them well-suited for low to medium frequency applications such as broadcast radio and television. Dipole antennas are also easy to construct and relatively inexpensive, making them a popular choice for hobbyists and DIY enthusiasts.
The length of this antenna is generally taken as half the wavelength of the EM wave that will be used for data transmission. The reason for this is explained by the properties of a sinusoidal wave and this video provides an excellent insight into it.
Consider a 104 MHz wave which is generally used in FM Radio. The wavelength is approximately 2.88m for the wave travelling in free space. This makes the length of the dipole approximately 1.44m. The calculations can then be adjusted for different media and the dimensions of the dipole can be adjusted accordingly. Generally, during the design process, advanced software such as Ansys HFSS or Dassault System’s CST is used for optimising the dimensions and analysing the results.
Yagi-Uda Antenna
The Yagi-Uda antenna, named after its Japanese inventors Hidetsugu Yagi and Shintaro Uda, is a type of directional antenna widely used for both transmitting and receiving radio signals. It consists of a driven element, such as a dipole, and several parasitic elements, such as reflectors and directors, that are positioned in a specific arrangement to increase the antenna’s directivity and gain. Yagi-Uda antennas are typically used in applications where a focused beam of radio energy is required, such as long-range communication, amateur radio, and television reception. They are also relatively easy to construct and are relatively inexpensive compared to other directional antennas. Most readers would be familiar with this antenna as it was widely used in homes and offices with cable television before DTH television systems took over.
The basic functioning of a Yagi-Uda consists of two parts. Generating the EM wave and directing the said wave. The driven element, which is what radiates the EM wave is generally a dipole antenna. The directors and reflectors are what make this antenna a directional one as compared to the dipole, which is omnidirectional.
As we will see further along this post, the gain of the antenna is related to the amount of power radiated in a particular direction. In directional antennas, the aim is to concentrate all of the power in a particular direction allowing a higher gain which then affects several desirable properties such as loss minimisation, transmission range etc. In a Yagi-Uda antenna, the reflectors are responsible for concentrating the radiated power in a particular direction.
Let us consider a Yagi-Uda with a single reflector. It is placed at a specific interval from the driven element and in the direction opposite to the desired direction of radiation. Putting it simply, EM waves are radiated at specific time intervals from the source in all directions. When the wave is incident on the reflector, the reflected wave then forms a constructive interference with the radiated wave from the source in the next pulse in the desired direction.
The directors are elements placed in the direction of the desired direction of radiation. They are responsible for focusing the radiation with respect to the half-power beamwidth (which will be discussed later in this blog). A good explanation is provided in the video below.
Parabolic Antenna
Parabolic antennas, also known as dish antennas, are highly directional antennas that consist of a parabolic reflector and a feed element placed at the reflector’s focal point. The parabolic shape of the reflector focuses incoming or outgoing radio waves into a narrow beam, providing high gain and directivity. Parabolic antennas are commonly used in satellite communication, microwave communication, and radar systems, where long-range communication and high signal quality are required. They are also used in terrestrial wireless communication systems, where a narrow beam is required to reach a distant location or to overcome obstructions.
Parabolic antennas consist of a parabolic reflector made of metal or conductive material, such as metal mesh or sheet, and a feed element placed at the reflector’s focal point. The reflector’s shape is designed to focus incoming or outgoing radio waves into a narrow beam. The feed element can be a dipole, a patch antenna, or any other type of antenna that matches the desired frequency range and polarization. To maximize the performance of the antenna, the reflector and feed element must be precisely aligned and optimized for the specific frequency range.
When radio waves reach the parabolic reflector, they are reflected and focused toward the feed element, where they are combined and transmitted or received. The focus of the parabolic reflector is chosen to provide the highest possible gain and directivity, making the antenna highly directional and well-suited for long-range communication. The reflector’s surface must be smooth and well-finished to minimize any surface imperfections that could cause reflections or distortions in the signal.
In summary, parabolic antennas are highly directional antennas that consist of a parabolic reflector and a feed element. They are designed to focus incoming or outgoing radio waves into a narrow beam, providing high gain and directivity for long-range communication. The performance of parabolic antennas is dependent on the accuracy of the reflector’s shape, the alignment of the feed element, and the smoothness of the reflector’s surface.
Basic Antenna Parameters
Designing an antenna requires a deep understanding of various parameters that affect its performance, including its operating frequency, gain, directivity, impedance, and polarization. These parameters determine the quality and reliability of the wireless communication system and are critical in selecting the right type of antenna for a specific application.
Let’s look at some of the basic parameters that must be taken into account before beginning the design process.
Operating Frequency
The operating frequency of an antenna refers to the frequency range for which the antenna is designed to operate efficiently. It is a crucial design parameter that affects the performance of an antenna and must be carefully considered when designing a wireless communication system. For example, an antenna designed for the 2.4 GHz frequency band, commonly used for Wi-Fi and Bluetooth, may not work well for the 700 MHz frequency band used for mobile phone communication. Similarly, an antenna designed for GPS communication at 1575 MHz may not be suitable for the X-band radar at 10 GHz. It is important to choose the right operating frequency for the specific application to ensure optimal performance of the antenna and the wireless communication system. Some antennas, known as broadband antennas, can operate over a wide frequency range, while others are designed for specific frequency bands. Understanding the operating frequency of an antenna is crucial for ensuring effective and efficient wireless communication
Gain
Antenna gain is a measure of the ability of an antenna to direct and amplify the radio signals it transmits or receives. It is expressed in decibels (dB) relative to an isotropic antenna, which is a theoretical antenna that radiates equal power in all directions. Antenna gain indicates the level of concentration of the radio waves in a specific direction, and higher gain means that the antenna can focus more power in a narrower beam, increasing the range and reliability of the wireless communication system.
There are different types of gain, including directivity gain and effective isotropic radiated power (EIRP) gain. Directivity gain is the ratio of the power radiated in a specific direction to the power radiated by an isotropic antenna in the same direction. EIRP gain is the combination of directivity gain and the power supplied to the antenna by the transmitter. The gain of an antenna affects its radiation pattern and directivity, and must be carefully considered when selecting an antenna for a specific application. A higher gain antenna may provide a stronger signal and longer range, but it may also be more directional and less flexible in its coverage area
Directivity
Antenna directivity is a measure of the concentration of the antenna’s radiated power in a specific direction. It is a key factor in determining the range and performance of a wireless communication system, as it affects the strength and focus of the signals transmitted or received by the antenna. Directivity is often expressed in terms of the antenna’s gain, which is a measure of the concentration of the radiated power in a specific direction relative to an isotropic antenna, which is a theoretical antenna that radiates equal power in all directions.
There are different types of antenna directivity, including omnidirectional, directional, and highly directional antennas. Omnidirectional antennas radiate equal power in all directions and are often used for applications such as Wi-Fi where signals need to be transmitted or received in all directions. Directional antennas focus the radiated power in a specific direction, increasing the signal strength in that direction and providing a longer range. Highly directional antennas, such as Yagi-Uda or parabolic antennas, concentrate the radiated power in a very narrow beam, providing even greater range and signal strength. The directivity of an antenna must be carefully considered when selecting an antenna for a specific application, as it affects the range and performance of the wireless communication system
Gain and directivity are directly related to each other.
Half Power Beamwidth (HPBW)
The half-power beamwidth (HPBW) of an antenna is a measure of the width of its main lobe, or the region in which the majority of its radiated power is concentrated. It is defined as the angle between the two points on the radiation pattern where the power is reduced to half of its maximum value. The HPBW is an important parameter in determining the directivity and gain of an antenna, as it affects the width of the beam of radio waves that are transmitted or received.
In general, the HPBW of an antenna is inversely proportional to its gain, meaning that a higher gain antenna will have a narrower HPBW and a more focused beam of radio waves. This is why highly directional antennas, such as Yagi-Uda or parabolic antennas, have a smaller HPBW and a more focused main lobe compared to omnidirectional or directional antennas. The HPBW of an antenna must be considered when selecting an antenna for a specific application, as it affects the range and performance of the wireless communication system. A smaller HPBW may provide a longer range and greater signal strength, but it may also result in a more directional and less flexible coverage area
Impedance and Impedance Matching
Antenna impedance refers to the amount of electrical resistance offered by an antenna to the flow of alternating current (AC) in its electrical circuit. The impedance of an antenna affects its ability to transfer energy from the transmitter to the radiated waves and from the received waves to the receiver. A mismatch between the impedance of the antenna and the transmission line, such as a coaxial cable, can result in a significant loss of energy and degradation of the signal quality.
Impedance matching is the process of ensuring that the impedance of the antenna and the transmission line are equal, allowing for maximum power transfer and minimizing loss. In practice, the majority of transmitters and receivers use a 50 ohm feed line, and therefore, the antenna should be designed to have a 50 ohm impedance to ensure good impedance matching. The impedance matching can be achieved through the use of matching networks, such as transformer networks, that adjust the impedance of the antenna to match the 50 ohm feed line.
In summary, impedance matching is a critical aspect of antenna design and must be carefully considered to ensure optimal performance and efficiency of the wireless communication system. The use of a 50 ohm feed line and matching the impedance of the antenna to 50 ohms can significantly improve the signal quality and power transfer efficiency of the system
Voltage Standing Wave Ratio (VSWR)
The voltage standing wave ratio (VSWR) is a measure of the degree of impedance mismatch between the antenna and the transmission line. It is defined as the ratio of the maximum to minimum voltage along the transmission line and is a dimensionless value typically expressed in decibels. A VSWR of 1:1 represents an ideal impedance match, meaning that there is no reflection of the signal and all the energy is being transferred from the transmitter to the antenna and vice versa.
A VSWR greater than 1:1 indicates an impedance mismatch, which results in a portion of the signal being reflected back towards the transmitter, leading to a reduction in signal quality and power transfer efficiency. The VSWR can be used as an indicator of the degree of impedance mismatch, and as a measure of the quality of the antenna system, allowing for easy detection of problems such as mismatched antennas or faulty transmission lines.
In summary, the VSWR is a useful metric in antenna design and implementation, as it provides a simple and reliable way of measuring the impedance match between the antenna and the transmission line. By ensuring a low VSWR, it is possible to optimize the performance and efficiency of the wireless communication system
Polarisation
Polarization in antenna theory refers to the orientation of the electric field of the radio waves as they travel through space. There are two main types of polarization: linear and circular. Linear polarization refers to a wave that has an electric field that is oriented in a specific direction, either vertically or horizontally. Circular polarization refers to a wave that has an electric field that rotates in a circular direction.
In practice, the choice of polarization for an antenna depends on the application and the environment in which it is operating. For example, vertically polarized antennas are commonly used in mobile communication systems, as they are less affected by the multi-path fading that occurs in urban environments. Horizontally polarized antennas are typically used in broadcast applications, where the signal needs to cover a large area. Circular polarization is often used in satellite communication systems, as it provides a more stable signal and is less affected by orientation changes.
In summary, polarization is an important factor in antenna design and implementation, as it affects the transmission and reception of the signal, and can have a significant impact on the performance of the wireless communication system. The choice of polarization must be carefully considered and optimized to ensure optimal performance and efficiency of the system
To summarise what we’ve seen so far, you should ask yourself these questions to begin designing an antenna:
- What is the operating frequency of my wireless system?
- Should the antenna be omnidirectional, bidirectional or just radiate in one direction?
- If it is not omnidirectional, how directional should it be, i.e what should be the maximum gain and directivity I hope to achieve?
- Great! I have these specifications decided. Now, which antenna should I go with? I could go with a rectangular patch antenna if I want it to radiate in just one direction.
- Based on my operating frequency, what would be the ideal dimensions of this antenna?
- Ok, I have everything decided and noted down. What should I do now?
We’ll get to answering the last question in the next section, but first here’s an important thing to note.
As we know, results from theoretical calculations and practical results differ. You may want to design a dipole antenna of length 0.5m for a 300 MHz operating frequency. But these calculations will yield results different from the practical results due to the various assumptions taken during the theoretical modelling. For this reason, it is necessary to simulate the antenna design assuming a real-world environment that can produce losses in the antenna, tune the antenna parameters till the desired result is obtained, and then proceed to use the final design for fabrication.
This brings us to the next section.
Tools and Software for Antenna Design
Three of the most commonly used tools and software for antenna design are — Ansys HFSS, Dassault System’s CST Studio Suite and MATLAB
Ansys HFSS
ANSYS HFSS is a high-frequency electromagnetic simulation software that is commonly used for antenna design and analysis. It is a powerful tool that allows engineers to model and analyze the behaviour of antennas in a virtual environment, taking into account a wide range of parameters such as frequency, polarization, and the surrounding environment. The software provides a range of advanced simulation capabilities, including 3D full-wave electromagnetic field simulations, multiple excitation sources, and complex geometries.
ANSYS HFSS provides designers with an accurate and efficient method of analyzing and optimizing their antenna designs. It enables designers to evaluate different design alternatives and make trade-off decisions before building prototypes, reducing time and cost in the design process. In addition, the software also provides visualization tools to help designers understand the behaviour of their antennas and to identify areas for improvement.
In summary, ANSYS HFSS is an essential tool for antenna design, providing a comprehensive and accurate simulation environment for the development of high-performance antennas. Its capabilities allow designers to evaluate their designs, identify problems, and make improvements before prototypes are built, making it a valuable tool for engineers and researchers working in the field of antenna design
Check out their website. They also provide a student version which is free to use but with limited features.
CST Studio Suite
CST Studio Suite is a comprehensive simulation software package that is widely used for the design and analysis of antennas and other electromagnetic devices. It provides a range of advanced simulation tools, including 3D full-wave electromagnetic field simulations, time-domain simulations, and circuit simulations, making it a versatile and powerful tool for antenna designers.
The software’s intuitive user interface, combined with its robust simulation capabilities, makes it an ideal choice for engineers and researchers looking to analyze and optimize their antenna designs. CST Studio Suite provides a wide range of visualization and post-processing tools, allowing designers to analyze their designs in detail and identify areas for improvement.
In addition, CST Studio Suite is also well-suited for the simulation of complex systems, such as multiband and broadband antennas, as well as antenna arrays, making it a valuable tool for designers working in a wide range of applications, including communications, radar, and medical equipment.
Find more information on their website
MATLAB
MATLAB is a widely used software platform for engineering and scientific applications, including antenna design and analysis. It provides a comprehensive set of tools for mathematical and numerical analysis, making it a valuable resource for antenna designers.
MATLAB allows engineers and researchers to develop and simulate antenna models, evaluate their performance, and optimize their designs. It provides a range of built-in functions for antenna analysis, including radiation pattern analysis, antenna impedance calculation, and antenna optimization. Additionally, it also has toolboxes that are specifically designed for antenna design, such as the Antenna Toolbox.
The Antenna Toolbox provides designers with an extensive library of antenna elements, allowing them to quickly and easily model different antenna geometries and configurations. It also includes advanced simulation and optimization tools, enabling designers to evaluate their designs and make trade-off decisions before building prototypes
Final Steps
Simulating the antenna design on a software allows you to make certain changes to the design and fine-tune the parameters to enhance its performance. Keep in mind that the simulated results will also vary from the actual results observed from the antenna that’s custom-made according to your design. Hence, it is necessary to achieve performance scores much higher than your requirements during simulation.
Once this is done, it is now time to bring your creation into the real world. The fabrication process for antennas such as rectangular patches, or printed dipoles is pretty straightforward and I’ll cover this in some future blog. Until then, you can simply hand over the design to a commercial manufacturer, or any educational institute equipped with the tools and machines to fabricate an antenna.
Closing Notes
This guide should’ve equipped you with the basics that an engineer in the field of antenna design MUST know. Although it’s a lot of theory, the efforts one takes to go through it pay off in the end.
Electromagnetics is a field whose science can only be described as beautiful and elegant. The mathematics behind it, while greek to most people (both literally and figuratively) goes from being very confusing and boring to quite interesting once you start understanding it in bits and pieces.
In future posts, we’ll take a look at some other concepts of electromagnetism along with both theoretical and practical approaches to understanding some of them. I’ll also create a few tutorial blogs on some really cool projects you can build based on various concepts of EM waves (how about a signal jammer to begin with?)
Finally, feel free to share your thoughts, questions, suggestions, etc. in the comments section below.
