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Mahmood Gusev
Mahmood Gusev

Antenna and Wave Propagation by K.D. Prasad: A Review of the Book and Its Topics



Antenna And Wave Propagation By Kd Prasad Pdf Free 1370




If you are looking for a comprehensive and up-to-date book on antenna and wave propagation, you might want to check out the book by Kd Prasad. This book covers all the essential topics in this field, from basic concepts to advanced applications. In this article, we will give you an overview of what this book is about, what are the main topics covered, and how you can download it for free.




Antenna And Wave Propagation By Kd Prasad Pdf Free 1370



Introduction




What is antenna and wave propagation?




An antenna is a device that converts electrical signals into electromagnetic waves, or vice versa. It is used for transmitting and receiving information over a distance. An antenna can be classified into different types based on its shape, size, frequency range, radiation pattern, polarization, etc.


Wave propagation is the study of how electromagnetic waves travel through different media, such as free space, air, water, or earth. Wave propagation can be affected by various factors, such as reflection, refraction, diffraction, scattering, absorption, polarization, etc.


Why is antenna and wave propagation important?




Antenna and wave propagation are important because they are the basis of many applications in communication, radar, navigation, remote sensing, broadcasting, etc. Antenna and wave propagation enable us to send and receive information wirelessly over long distances. They also help us to understand the nature of electromagnetic waves and how they interact with different environments.


What are the main topics covered in the book by Kd Prasad?




The book by Kd Prasad is one of the most popular books on antenna and wave propagation. It covers both theoretical and practical aspects of this field. It has 1282 pages and 14 chapters. The main topics covered in this book are:



  • Antenna Basics



  • VHF, UHF and Microwave Antennas - I



  • VHF, UHF and Microwave Antennas - II



  • Antenna Arrays



  • Aperture Antennas



  • Slot Antennas



  • Biconical Antennas



  • Spiral Antennas



  • Frequency Independent Antennas



  • Log Periodic Antennas



  • Antenna Measurements



  • Wave Propagation Fundamentals



  • Sky Wave Propagation



  • Ground Wave Propagation



The book also contains numerous examples, problems, diagrams, and tables to illustrate the concepts and applications. It is written in a clear and concise manner, suitable for both students and professionals.


Antenna Basics




Basic antenna parameters and patterns




Some of the basic antenna parameters that are used to describe the performance and characteristics of an antenna are:



  • Radiation pattern: The spatial distribution of the radiated power or field intensity from an antenna.



  • Beam area: The solid angle subtended by the main lobe of the radiation pattern.



  • Radiation intensity: The power radiated by an antenna per unit solid angle.



  • Beam efficiency: The ratio of the power radiated in the main lobe to the total power radiated by an antenna.



  • Directivity: The ratio of the radiation intensity in a given direction to the average radiation intensity over all directions.



  • Gain: The ratio of the radiation intensity in a given direction to the radiation intensity that would be obtained from an isotropic antenna (an ideal antenna that radiates equally in all directions).



  • Resolution: The ability of an antenna to distinguish between two closely spaced sources of radiation.



  • Antenna aperture: The effective area of an antenna that intercepts the incident power.



  • Effective height: The height of an antenna above the ground that produces the same field strength as the actual antenna.



An antenna pattern is a graphical representation of the radiation pattern. It can be plotted in different coordinate systems, such as rectangular, polar, or spherical. An antenna pattern can be divided into two parts: the main lobe and the side lobes. The main lobe is the region where the radiation intensity is maximum, and the side lobes are the regions where the radiation intensity is lower than the main lobe. The side lobes are usually undesirable, as they cause interference and waste power.


Fields from oscillating dipole and field zones




An oscillating dipole is a simple model of an antenna that consists of a short wire carrying an alternating current. It can be used to study the basic principles of radiation and wave propagation. The fields from an oscillating dipole can be calculated using Maxwell's equations or vector potentials. The fields can be classified into three zones, depending on the distance from the dipole:



  • Near field zone: The region close to the dipole, where the fields are reactive and non-radiating. The near field zone extends up to a distance of λ/2π, where λ is the wavelength of the radiation.



  • Radiating near field zone (Fresnel zone): The region between the near field zone and the far field zone, where the fields are partially reactive and partially radiating. The radiating near field zone extends up to a distance of 2D^2/λ, where D is the length of the dipole.



  • Far field zone (Fraunhofer zone): The region far away from the dipole, where the fields are purely radiating and spherical. The far field zone begins at a distance of 2D^2/λ from the dipole.



Antenna theorems and radiation




Some of the important antenna theorems that relate to radiation are:



  • Reciprocity theorem: This theorem states that if an antenna A excites an antenna B with a certain amount of power, then antenna B will excite antenna A with the same amount of power when they are interchanged. This implies that antennas have identical transmitting and receiving characteristics.



  • Huygens' principle: This principle states that every point on a wavefront can be considered as a source of secondary spherical waves, and that the new wavefront is the envelope of these secondary waves. This principle can be used to analyze diffraction and reflection phenomena.



  • Helmholtz theorem: This theorem states that any vector field that satisfies certain conditions can be expressed as a sum of a gradient field and a curl field. This theorem can be used to derive expressions for electric and magnetic fields in terms of scalar and vector potentials.



Radiation is the process by which electromagnetic waves are emitted by an antenna. Radiation can be explained by using either physical optics or electromagnetic theory. Physical optics treats radiation as a result of interference between direct and reflected waves on a surface. Electromagnetic theory treats radiation as a result of acceleration or deceleration of charges in a conductor. Radiation can be characterized by using parameters such as radiation resistance, power density, Poynting vector, etc.


Thin linear wire antennas and their characteristics




A driven element and reradiate them with a different phase. This modifies the radiation pattern of the driven element and enhances the gain in certain directions. A common example of an array with parasitic elements is the Yagi-Uda array, which consists of a driven dipole, a reflector, and one or more directors. The reflector is slightly longer than the driven dipole and placed behind it, opposite to the direction of transmission. The directors are slightly shorter than the driven dipole and placed in front of it, in the direction of transmission. The Yagi-Uda array can achieve high gain and directivity by using a relatively small number of elements. It is widely used for television, radio, and wireless communication applications.


Folded dipoles and their characteristics




A folded dipole is a type of antenna that consists of a single wire bent into a loop with a gap at one point. It can be considered as two identical dipoles connected in parallel. A folded dipole has several advantages over a simple dipole, such as:



  • It has a higher input impedance, which makes it easier to match with a transmission line.



  • It has a wider bandwidth, which means it can operate over a larger range of frequencies.



  • It has a lower Q factor, which means it has less reactance and less loss.



  • It has a higher radiation efficiency, which means it radiates more power for a given input power.



A folded dipole can be used as a driven element in an array antenna, such as a Yagi-Uda array or a log-periodic array. It can also be used as a standalone antenna for receiving or transmitting signals.


Helical antennas and their modes




A helical antenna is a type of antenna that consists of a wire wound into a helix shape around a cylindrical or conical support. The helix can have one or more turns, depending on the desired characteristics. A helical antenna can operate in two modes: normal mode and axial mode.



  • In normal mode, the helix has a small circumference compared to the wavelength of the radiation. The radiation pattern is similar to that of a dipole, with maximum radiation perpendicular to the axis of the helix. The polarization is linear along the axis of the helix. The normal mode is used for low-frequency applications, such as AM radio broadcasting.



  • In axial mode, the helix has a large circumference compared to the wavelength of the radiation. The radiation pattern is similar to that of an end-fire array, with maximum radiation along the axis of the helix. The polarization is circular around the axis of the helix. The axial mode is used for high-frequency applications, such as satellite communication and radio astronomy.



A helical antenna can achieve high gain and directivity by using a relatively small size and weight. It can also be easily adjusted for different frequencies by changing the pitch angle or the number of turns of the helix. 71b2f0854b


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