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Lect31WireAntennas

Lect31WireAntennas - ECE 3030 Electromagnetic Fields and...

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1 ECE 3030 Electromagnetic Fields and Waves Fall 2009 Lecture 31 2009/11/9 Wire Antennas Short Dipole Antennas Half Wave Dipole Antennas 1 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 31: Instructor: Dr. Wesley E. Swartz Half-Wave Dipole Antennas Three-Half-Wave Dipole Antennas Small Wire Loop Antennas (Magnetic Dipole Antennas) Problem Assignments Demo 11 Problems (Tuesday, November 10) : Problem 17.2: Pattern produced by two Hertzian dipole antennas. Problem 17.4: Pattern produced by one Hertzain dipole and reflector. Problem 17.20: Wireless link between two half-wave dipoles. Workshop 11 (Thursday, November 12) : Problem 17.3: Finding required antenna element spacing and phase for given pattern. Problem 17.21: Characteristics of an N-turn loop antenna. 2 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 31: Homework 11 Problems (due Tuesday, November 17) : Problem 17.1: Plot radiation pattern for two Hertzian dipole antennas. Problem 17.12: The radiation resistance of a Hertzian dipole. Problem 17.23: Transmission-receiption between dipole and loop. Extra Credit Problems from Last Lecture (due Monday, November 23) : See Lecture 30 notes for details. MatLab code and plots must be sent via Email. Simplified Smith Chart for Prelim 3 I will give a simplified Smith Chart such as this one. r=1 g=1 x circle segments b circle segments At least one | Γ | circle. You will need to identify 4 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 31: Circles Points Angles Some parts may be multiple choice true/false need approximations need minimal computations Center-Fed Wire Antennas Consider the following wire antenna fed via a transmission line:     y x z I z r J ˆ If one is interested in radiation far-fields only, then assume: r d  d Z o x z I 2  d 5 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 31:     ' dz e ' z I e r 4 z ˆ ' dz e ' z I r 4 z ˆ r A ' dz e ' z z ˆ r ' z I 4 z ˆ ' dv e ' r r 4 ' r J r A cos ' z k j 2 d 2 d r k j o ' z z ˆ r k j o ff ' z z ˆ r k j o ' r r k j o  2 , Far-field approximation - also called the Fraunhoffer approximation           cos ˆ sin sin ˆ cos sin ˆ ˆ z y x r Recall that: Center-Fed Short Dipole Wire Antenna (1) Short dipole wire antenna fed via a transmission line:     y x z I z r J ˆ d Z o x z I 2  d Short dipole Make an assumption for the current distribution on the antenna – a triangular distribution z I d/2 I ( z ) 6 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009
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