Lect34Reflectors

# Lect34Reflectors - ECE 3030 Electromagnetic Fields and...

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1 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 34: ECE 3030 Electromagnetic Fields and Waves Instructor: Dr. Wesley E. Swartz Fall 2009 Lecture 34 2009/11/16 Antenna Dishes (Reflectors)

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2 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 34: Problem Assignments Demo 12 (Tuesday, November 17) : Problem 17.8: Antenna pattern from a corner reflector. Problem 17.10: Two-dimensional array of half-wave dipoles. No Workshop 12 – Prelim 3! (Thursday, November 19) : Covers Dielectric interfaces Impedance matching with dielectrics and transmission line stubs Transmission line transients Antenna patterns from radiating elements Smith Chart usage Waveguides Bring a calculator, straight-edged ruler, 3 sheets of notes. Homework 12 (due Tuesday, November 24) : Problem 17.11: CUPRI array at Isabela, Puerto Rico. Note: There was a quarter wave of phase progression provided by the feed network to the 8 COCOs. Problem 17.15: Half-wave dipole above a reflector.
3 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 34: A Short Dipole Antenna Gain: Pattern: x y φ ( 29 ( 29 θ 2 sin 2 3 , = G ( 29 ( 29 2 sin , = p ( 29 π , 2 = p In the x-y ( = π /2) plane the radiation goes everywhere – not a very efficient antenna.

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4 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 34: Question: How does one get all the radiation from a Hertzian dipole to go in the + x direction? Answer: Use a reflector. Array Factor: A Plane Reflector with a Short Dipole Feed (1) The basic idea behind reflector antennas is that metal surfaces can be used to direct radiation from antennas in desired directions (or vice versa in reception). x y x y a a image dipole φ feed ( 29 ( 29 ( 29 [ ] - = 2 φ 2 π for 0 2 π φ 2 π for φ cos θ sin ka 4sin φ θ, F 2 2 { ,....... 5 , 3 , 1 2 = = n n ka π { ,....... 5 , 3 , 1 4 = = n n a λ For maximum gain in the θ = π /2 , Φ = 0 direction, choose:
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Lect34Reflectors - ECE 3030 Electromagnetic Fields and...

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