tailieunhanh - Lecture Wireless and mobile computing – Chapter 15: Antennas and propagation

The following will be discussed in this chapter: Electric and magnetic field coupling; EM radiations; period, frequency, and wavelength; phase lag and phase lead; antennas why??? antenna analogy; why separate TX and RX antennas transmission are required; transmission line as an antenna; working of an antenna; far and near fields; antennas characteristics. | Antennas and Propagation Lecture 15 Overview Electric and Magnetic Field Coupling EM Radiations Period, Frequency, and Wavelength Phase Lag and Phase Lead Antennas Why??? Antenna Analogy Why Separate TX and RX Antennas Transmission are Required Transmission Line as an Antenna Working of an Antenna Far And Near Fields Antennas Characteristics Polarization Antenna and Wavelength Antenna Gain Antenna Length Electric and Magnetic Field Coupling Electric Field Electric and Magnetic Fields Coupling Electric and Magnetic Field Coupling two laws (from Maxwell Equation) 1. A Moving Electric Field Creates a Magnetic (H) field 2. A Moving Magnetic Field Creates an Electric (E) field Magnetic Field Lines are closed loops surrounding the currents that produce them Electromagnetic (EM) radiation Electromagnetic (EM) radiation is caused by charged particles that are accelerated. Charged particles have an electric field. Moving charged particles create a magnetic field, which in turn creates electromagnetic radiation sometimes called an electromagnetic wave or electromagnetic field. Therefore, changing currents are required to create electromagnetic radiation. Electromagnetic radiation has both a magnetic and electric field. Period, Frequency, and Wavelength T = period, time for one cycle f = frequency (cycles/s = Hz) = 1/T λ = wavelength (m) c = speed of light in vacuum = 3E8 m/s c= λ*f What is T, f, and λ? Ans: 2 s, Hz, 6E8 m Phase (time delay) Phase: relative timing of two signals Could measure absolute time like seconds More common to use a radians or degrees Signal 1 = sin(θ) Signal 2 = sin(θ-pi/4) Phase Lag Phase Lead Why Antenna ??? A general model of all communication systems. Analogy You need to understand the basics of communications. You have one side sending a message and one receiving it. Our ears work like antennas. We can capture vibrations between 20 Hz and 20,000 Hz. So when we talk about antennas on electronics, . | Antennas and Propagation Lecture 15 Overview Electric and Magnetic Field Coupling EM Radiations Period, Frequency, and Wavelength Phase Lag and Phase Lead Antennas Why??? Antenna Analogy Why Separate TX and RX Antennas Transmission are Required Transmission Line as an Antenna Working of an Antenna Far And Near Fields Antennas Characteristics Polarization Antenna and Wavelength Antenna Gain Antenna Length Electric and Magnetic Field Coupling Electric Field Electric and Magnetic Fields Coupling Electric and Magnetic Field Coupling two laws (from Maxwell Equation) 1. A Moving Electric Field Creates a Magnetic (H) field 2. A Moving Magnetic Field Creates an Electric (E) field Magnetic Field Lines are closed loops surrounding the currents that produce them Electromagnetic (EM) radiation Electromagnetic (EM) radiation is caused by charged particles that are accelerated. Charged particles have an electric field. Moving charged particles create a magnetic field, which in turn .