Lecture 17 Antenna Fundamentals

Lecture 17 Antenna Fundamentals - Lecture Lecture17...

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cture 17 Lecture 17 Antenna Fundamentals ayt H 14 Hayt CH 14 1 McGill ECSE 352, Fall 2011, D. Davis
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adiation Radiation The basic component of all wireless systems is the antenna. The transmit antenna converts current and voltage to electric and magnetic fields. ese fields propagation until they strike the receiving These fields propagation until they strike the receiving antenna. The receiving antenna will convert the incident fields into ltage and current. voltage and current. The signal information is then processed by the system in the usual manner. e antenna works by radiating electromagnetic waves the The antenna works by radiating electromagnetic waves, the principles of radiation are the focus of this section of the lecture. McGill ECSE 352, Fall 2011, D. Davis 2
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adiation Radiation e first step will be to relate circuit behaviour The first step will be to relate circuit behaviour (voltage and current) to electromagnetic aves waves. This will be done through the use of potential nctions functions. There are two general classes of potential functions: scalar (e.g. Voltage) and vector potential functions. McGill ECSE 352, Fall 2011, D. Davis 3
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adiation Radiation r our purposes we will define the vector For our purposes we will define the vector magnetic potential (A) as: We can link this function to electric fields using Faraday’s Law: ׏ൈܧ ൌെ ߲ ሺ׏ൈ ܣ ҧ ሻ՜׏ൈ ቆܧ ߲ܣ ҧ ቇൌ0 In addition we can write scalar potential: ߲ݐ ߲ݐ McGill ECSE 352, Fall 2011, D. Davis 4
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adiation Radiation is can be written as: This can be written as: ܧ ൌെቆ׏ܸ൅ ߲ܣ ҧ ߲ݐ Note that the first term in the brackets represents the traditional static electric potential and the second represents the contribution due to time varying electromagnetic fields. McGill ECSE 352, Fall 2011, D. Davis 5
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adiation Radiation e will need to define the characteristics of We will need to define the characteristics of the potential function, starting with Ampere’s w: Law: ׏ൈ׏ൈ ܣ ҧ ൌߤܬ ҧ െߤ߳ ߲ ߲ݐ ቆ׏ܸ ൅ ߲ܣ ҧ ߲ݐ From this ׏ 2 ܣ ҧ ߲ 2 ܣ ҧ ߲ݐ 2 ൌെߤܬ ҧ ൅׏ ൤ߤ߳ ߲ܸ ߲ݐ ൅ ሺ׏· ܣ ҧ ሻ൨ This will require a definition for the divergence of the potential function. McGill ECSE 352, Fall 2011, D. Davis 6
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adiation Radiation ne choice for the divergence of the potential One choice for the divergence of the potential is developed by Lorentz (called the Lorentzian auge): Gauge): When using this definition for the divergence of the potential we can write: ׏ 2 ܣ ҧ െߤ߳ ߲ 2 ܣ ҧ ߲ݐ 2 ൌെߤܬ ҧ McGill ECSE 352, Fall 2011, D. Davis 7
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adiation Radiation is relationship for the potential is called the This relationship for the potential is called the non homogeneous wave equation for vector otential A potential A .
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This note was uploaded on 12/03/2011 for the course ECSE 352 taught by Professor Mi during the Fall '10 term at McGill.

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Lecture 17 Antenna Fundamentals - Lecture Lecture17...

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