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Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1
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Page 1: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

1

Prof. David R. JacksonECE Dept.

Spring 2014

Notes 9

ECE 6341

Page 2: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

2

Circular Waveguide

a

z

TMz mode:

, ,zA z

( ) sin( )

( ) cos( )zjk z

J ke

Y k

2 2 2zk k k

r

The waveguide is homogeneously filled, so we have independent TEz and TMz modes.

Page 3: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Circular Waveguide (cont.)

(1) variation [0,2 ]

( , 2 , ) ( , , )z z

Choose

(uniqueness of solution)

cos( )n

n

( )cos( )

( )z

n jk z

n

J kn e

Y k

Page 4: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

4

(2) The field should be finite on the z axis 0, , z

( )nY k is not allowed

cos( ) ( ) zjk znn J k e

Circular Waveguide (cont.)

2 2 2zk k k

Page 5: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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(3) B.C.’s: , , 0zE a z

22

2

2 2

2

1

1

z

z

E kj z

k kj

k

j

so ( , , ) 0a z

Circular Waveguide (cont.)

( ) 0nJ k a Hence

Page 6: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

6

( ) 0nJ k a

xn1 xn2

xn3

x

Jn(x) Plot shown for n 0

npk a x

Circular Waveguide (cont.)

npxk

a

Note: is not included since (trivial soln.)0 0nx 0n npJ xa

Page 7: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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TMnp mode:

cos( ) 0,1,2zjk zz n npA n J x e n

a

1/ 22

2 1,2,3,.........npz

xk k p

a

Circular Waveguide (cont.)

Page 8: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Cutoff Frequency: TMz

npxk k

a

2 npc

xf

a

2TM

c np

r

cf x

a

0zk

2 2 2zk k k

Page 9: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Cutoff Frequency: TMz (cont.)

TM01, TM11, TM21, TM02, ……..

p \ n 0 1 2 3 4 5

1 2.405 3.832 5.136 6.380 7.588 8.771

2 5.520 7.016 8.417 9.761 11.065 12.339

3 8.654 10.173 11.620 13.015 14.372

4 11.792 13.324 14.796

xnp values

Page 10: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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TEz Modes

, ,zF z

cos( ) ( ) zjk znn J k e

2

z

kH

j

, , 0a z Note:

Page 11: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Set , , 0E a z

1

0a

E

TEz Modes (cont.)

so

( ) 0nJ k a Hence

Page 12: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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1,2,3,.....

np

np

k a x

xk p

a

( ) 0nJ k a

TEz Modes (cont.)

x'n1 x'n2

x'n3

x

Jn' (x) Plot shown for n 1

Note: p = 0 is not included (see next slide).

1( ) ~ , 0,1,2,....

2 !n

n nJ x x n

n

Recall :

Page 13: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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TEz Modes (cont.)

cos( ) 1,2,zjk zn npn J x e p

a

Note: If p = 0 0npx

0 0n np nJ x Ja

(trivial soln.)0n

0n 0 0 0 1npJ x Ja

zjk z jkze e (trivial fields)

0k

Page 14: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Cutoff Frequency: TEz

npxk k

a

2 npc

xf

a

2TE

c np

r

cf x

a

0zk

2 2 2zk k k

Page 15: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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TE11, TE21, TE01, TE31, ……..

p \ n 0 1 2 3 4 5

1 3.832 1.841 3.054 4.201 5.317 5.416

2 7.016 5.331 6.706 8.015 9.282 10.520

3 10.173 8.536 9.969 11.346 12.682 13.987

4 13.324 11.706 13.170

x´np values

Cutoff Frequency:TEz

Page 16: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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TE11 Mode

TE10 mode of rectangular waveguide

TE11 mode of circular waveguide

The dominant mode of circular waveguide is the TE11 mode.

The TE11 mode can be thought of as an evolution of the TE10 mode of rectangular waveguide as the boundary changes shape.

Electric fieldMagnetic field

(from Wikipedia)

Page 17: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Attenuation Property of TE01 Mode

2d

cf

PP

21

2 td s

C

R H dl P

TEz Mode:2

2

1 1

1

z

z z

FH

j z

H k Fj

Assume that Fz is

order 1 as the frequency increases.

Goal: We wish to study the high-frequency dependence of attenuation on frequency for circular waveguide modes, and show the interesting behavior of the TE01 mode (the loss decreases as frequency increases).

1 1

2

2

sR

O

Recall that k is a constant.

Page 18: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Attenuation Property (cont.)

n = 0

1zH

O

(1) 0

0 0

nH

n

O

2

3/2

10d

O O

O

P

n 0

2

1/2

11d

P O O O

O

zk k O O

Note:

Page 19: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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From the TEz table:

2

1(1)

1(1)

z

z

FE E

FH H

j z

e.g.

e.g.

O

O

1f P OHence

Attenuation Property (cont.)

Page 20: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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If n = 0: 3/ 2c O

If n 0: 1/ 2c O

E

Hn = 0:

Attenuation Property (cont.)

Hence

Note: The mode TE0p mode can be supported by a series of concentric rings, since there is no longitudinal

(z-directed) current (H = 0).

Usual behavior for rectangular waveguides

Decreases with frequency!

Page 21: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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fc, TE11

f

ac

fc, TM01fc, TE21

fc, TE01

TE01

TE21

TE11

TM11 TM01

Attenuation Property (cont.)

1/ 2c O

3/ 2c O

Page 22: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Attenuation Property (cont.)The TE01 mode was studied extensively as a candidate for long-range communications – but was not competitive with antennas. Also, fiber-optic cables eventually became available with lower loss than the TE01 mode. It is still useful for some applications (e.g., high power).

From the beginning, the most obvious application of waveguides had been as a communications medium. It had been determined by both Schelkunoff and Mead, independently, in July 1933, that an axially symmetric electric wave (TE01) in circular waveguide would have an attenuation factor that decreased with increasing frequency [44]. This unique characteristic was believed to offer a great potential for wide-band, multichannel systems, and for many years to come the development of such a system was a major focus of work within the waveguide group at BTL. It is important to note, however, that the use of waveguide as a long transmission line never did prove to be practical, and Southworth eventually began to realize that the role of waveguide would be somewhat different than originally expected. In a memorandum dated October 23, 1939, he concluded that microwave radio with highly directive antennas was to be preferred to long transmission lines. “Thus,” he wrote, “we come to the conclusion that the hollow, cylindrical conductor is to be valued primarily as a new circuit element, but not yet as a new type of toll cable” [45]. It was as a circuit element in military radar that waveguide technology was to find its first major application and to receive an enormous stimulus to both practical and theoretical advance.

K. S. Packard, “The Origins of Waveguide: A Case of Multiple Rediscovery,” IEEE Trans. MTT, pp. 961-969, Sept. 1984.

Page 23: Prof. David R. Jackson ECE Dept. Spring 2014 Notes 9 ECE 6341 1.

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Attenuation Property (cont.)

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