4: Antennas
- Page ID
- 18963
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)In the previous two chapters we discussed energy conversion devices which are made from insulators and which are related to capacitors. In Chapters 4 and 5 we discuss energy conversion devices involving conductors and related to inductors. Maxwell's equations say that time varying electric fields induce magnetic fields and time varying magnetic fields induce electric fields. If a permanent magnet moves near a coil of wire, the time varying magnetic field will induce a current in the coil of wire. This idea is the basis behind motors and electrical generators, which are some of the most common energy conversion devices. However, they are outside the scope of this text because they involve magnets and coils. Instead, we will study two other types of energy conversion devices based on this same principle. In this chapter we discuss antennas, and in the next chapter we will discuss Hall effect devices.
- 4.1: Prelude to Antennas
- This page discusses antennas as devices that convert electrical energy to electromagnetic energy, serving as transmitters and receivers in various applications like cell phones and RFID tags. It covers basic antenna types, such as dipoles and monopoles, their designs, and efficiency, while also exploring theoretical aspects of energy conversion and the distinctions between fermions and bosons at the quantum level.
- 4.2: Electromagnetic Radiation
- This page covers antenna operation principles based on Maxwell's equations, highlighting superposition and reciprocity, which influence antenna design, power transmission, and reception characteristics. It outlines the differences between near field and far field radiation patterns, emphasizing their applications and the impact of environmental factors like soil properties on performance.
- 4.3: Antenna Components and Definitions
- This page explains antennas in radio frequency communication, distinguishing between driven elements, which are connected to power sources, and parasitic elements, which affect radiation patterns without direct connections. It covers various antenna forms and radiation patterns, including arrays.
- 4.4: Antenna Characteristics
- This page provides an overview of crucial factors for antenna selection, including frequency response, impedance, directivity, and polarization. It contrasts omnidirectional and directional antennas, detailing their unique characteristics and applications. The page also explains electromagnetic wave polarization, emphasizing the need for proper polarization matching in antenna design.
- 4.5: Problems
- This page covers key antenna concepts such as operating frequencies, bandwidth, and radiation patterns. It includes problems for calculating wavelengths and analyzing antenna attributes like parasitic elements.
Thumbnail: Animation of a half-wave dipole antenna transmitting radio waves, showing the electric field lines. (Public Domain; Chetvorno via Wikipedia)