ANTENG Ch11SAL031606

ANTENG Ch11SAL031606 - ECE 5318/6352 Antenna Engineering...

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Chapter 11 Chapter 11 Frequency Frequency Independent Independent Antennas Antennas ECE 5318/6352 ECE 5318/6352 Antenna Engineering Antenna Engineering Spring 2006 Spring 2006 Dr. Stuart Long Dr. Stuart Long
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2 ± THE BEGINING THE BEGINING Before 1950’s no antennas with bandwidth > 2 : 1 V.H. Rumsey V.H. Rumsey – University of Illinois 1955-1958 Antenna performance is typically a function of “ length / wavelength “ λ l ± Important characteristic Important characteristic
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3 ± SCALING PRINCIPLE SCALING PRINCIPLE Scale size by ratio of frequency and get similar behavior e.g. decrease antenna dimensions by factor of 2 and increase frequency by factor of 2 same performance (both are the same size in wavelengths) depends on some “characteristic length characteristic length
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4 ± SCALING PRINCIPLE SCALING PRINCIPLE (CONT) (CONT) Basic structural feature for frequency independent operation is the absence absence of any “characteristic length characteristic length self -scaling
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5 ± ANGLE PRINCIPLE ANGLE PRINCIPLE need a structure completely described by angles “ANGLE PRINCIPLE ANGLE PRINCIPLE α
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6 ± TRUNCATION PRINCIPLE TRUNCATION PRINCIPLE but practical structures need to be finite in size somehow currents need to fall off rapidly enough so that terminating the structure at some finite length does not alter its characteristics “TRUNCATION PRINCIPLE TRUNCATION PRINCIPLE
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7 ± TRUNCATION PRINCIPLE TRUNCATION PRINCIPLE (CONT) (CONT) infinite biconical infinite biconical infinite bi infinite bi -fin (bow tie) fin (bow tie) W h y n e d s u c b r o a ? e.g. TV. channels Jammers ± Example Example
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8 ± EQUIANGULAR SPIRAL EQUIANGULAR SPIRAL (log spiral) (log spiral) Boundaries given by a o e φ ρρ = Except for a rotation in space it looks the same for all frequencies
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9 ± EQUIANGULAR SPIRAL EQUIANGULAR SPIRAL (CONT) (CONT) Earlier work by H.G. Booker H.G. Booker on impedance relationship between a slot and its complementary dipole 4 1 2 2 2 2 = = = o o o o o d s Z Z Z ε μ
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10 ± EQUIANGULAR SPIRAL EQUIANGULAR SPIRAL (CONT) (CONT) if could somehow make an antenna and its complement the same, then the impedance would have to be constant, independent of frequency [] Ω = = = = 189 2 2 2 1 2 ' o o Z Z Z Z called “ SELF SELF -COMPLEMENTARY COMPLEMENTARY
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11 ± EQUIANGULAR SPIRAL EQUIANGULAR SPIRAL (CONT) (CONT) Dyson Dyson tried to build a self-complementary spiral; found a constant and radiation pattern over several octaves;
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This note was uploaded on 09/09/2010 for the course ECE 4436 taught by Professor Staff during the Spring '08 term at University of Houston.

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ANTENG Ch11SAL031606 - ECE 5318/6352 Antenna Engineering...

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