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1

Microwave &

Antenna (EL-354)

M.S. ALAM

Associate Professor

Department of Electronics Engineering

A.M.U. Al igarh

E- mail: [email protected]

Starting: 4

th

August 201 4



2

..ABOUT YOUR

TEACHER

..

1988: Bachelor of Engineering (Electronics & Communication Engineering)

1991 : Master of Engineering (Electronics

& Communication Engineering)

2002:

Doctorate degree (Ph. D)

(Electronics Engineering)

2010:

Post doctorate ( Nano- electronics

)

Visit website for more deta ils:

http://www.amu.ac.in/dshowfacultydata. jsp?did=32&eid=3208



Course

Structure



Course deals with..

+

µ

Waves fascinated human being due their

widespread use;

Antenna helps to broadcast signal waves

carrying messages and subsequently their

retrieval

µ

Waves Antenna



Dish TV

Music, news etc. are received through use of

µ

waves

ProgramGeneration

ProgramUpload

Satellite

DishAntenna

Receiver



RADAR

(radio detection and ranging)

Aircraft guidance, collision avoidance etc

Space Exploration

Monitoring of incoming microwave signals

from outer space or from other galaxies etc.

Medical Application

Selective heating of body organs, imaging ……

µ waves use are spreading in other numerous areas…



Less Crowded

Frequency

Spectrum

µwaves

2

4

3

1 igher

Bandwidth

Higher Speed

of Operation

Lower

Interference

Possible reasons



Objectives.

Familiarize the students about

importance of µwaves (1 - 300GHz)

How µwaves devices and circuits

work? and their applications

Obviously, various aspects of

µwaves will not be covered



Assessment

Course work will includes:

reporting to the class in time;

taking note of important points discussed in the class;

how well you respond when enquired about the subject;

home assignment etc.

Final

Semester

Exam, 60%

MidSemester

xam, 25%

CourseWork, 15%

Motive

Students take

interest in day

- to- day class

activities and

keep their notes

updated. .



Books

S. Y. Lio, “Microwave Devices & Circuits”

Prentice Hall of India, 2003 (Text book)

G. Kennedy and B. Davis,

“Electronic Communication Systems”, TMH,

1985

M. L. Sisodia & V. L Gupta, “Microwaves”,

New Age International Publishers, N. Delhi,

2001

J. D. Kraus, R. J. Marhefka & A. S. Khan,

“Antennas and Wave Propagation, ” 4th ed. ,

Tata McGraw- Hill, New Delhi, 201 0.



Books

C. G. Christodolou, P. F. Wahid,

“Fundamentals of Antennas: Concepts and

Applications” , PHI, N. Delhi, 2004.

M. M. Radmanesh, “Radio Frequency and

Microwave Electronics Illustrated”, Pearson

Education- 2001 .

Website address to access study materia ls:

http://www.amu.ac.in/showstudym.jsp?did=32&eid=3208



Study Plan

µwaves

components and their

working ----- Unit-I

Howhigh power µwaves

signals

generated & amplified ----- Unit II

How low power µwaves signals

generated & amplified -----Unit-III

Various types of antennas and their

applications ------Unit-IV

Focus

How µwaves devices

and c ircuits work?



µ

Wave

devices/circuits

Fr eq uen cy is h ig h

1GHz

Various parasitics (undesired circuit

elements) automatically cropped up

How to differentiate?

f< 1 GHz

f

p

ALL

pass

filter

f

p

f> 1 GHz

Band

pass

filter

Parasitics

Parasitics



…Which laws?

However, if devices are small in size (s< < λ), then lumped laws can

even be extended to µwave.

LF< 1 GHz

µwave/rf

Optical

f

Lumped laws e. m. laws Optical laws

1 GHz 300GHz

At µwave devices show up distributive nature i. e. v & i are

function of position x and e. m laws governed them.



dt

dH E µ

∫

⇒ KVL0 dl . EV 0 E

0 or0 If

1v

→

∞

ε

µε

Lumped laws can even be extended for

µ

wave elements provided their

sizes are small.

Insight…

j dt dE H +

ε

KCL0 .j H . ⇒

0 or0 If

1v

→

∞

ε

µε

Distributive,

where elements

are not loc alized

Lumped,

where

elements

have

been

localized

Ex:



HF Parameters

Y or Z or H–parameters are used for analysis for

LF<1GHz devices and circuits

net v (or net i) and SC (or OC) are used for their

description

Background

Ref: Mathew M. Radmanesh Book, pp. 287- 302 ; L io Book , pp. 1 41- 1 43

At

µ

waves, v and i become function of x and their

wave descriptions are required

…. Conventional Y/Z/H FAILS, because……



Reason being..

Non- availability of equipment to measure position

variable v or i

Short (SC) or open (OC) circuits are not possible to

carry out

Active devices become unstable when short

circuited



Why?

sc

V=0 ; I#0

OC

I=0 ; V#0

Y or

Z or H

can‘t be

applied



Alternate Solution

A proper tool to give port description for these

devices without actua lly harming the device

Use scattering (S) parameters for µwave

(> 1 GHz) devices



S-parameters

Easy to measure at

µ

wave frequencies

Based on transmitted and reflected

wave

Neither SC nor OC is required

SC could even harm the

µ

wave device

Similar kind of defining equation as

used for Y or Z or H

S-parameters in context with 2-port



S- parameters are wave descriptors that define the input- output relations

of a network in terms of incident and reflected waves

No. of Ports=2

2221212

2121111

aS aS b

aS aS b

+

+

=

22 21

12 11

SS

SSS

Similar defining equation as those of Y, Z or H parameters

/ ; / 022022 ZV b ZV a ii−

=

/ ; / 011011 ZV b ZV a ii−

=

[S]

2

×

2

a

1

b

1

a

2

b

2

Incident

Reflected



S

1 1

& S

21

Matched load Z0 is fully

absorptive i. e. all wave is

taken by load and nothing

is given out i. e. a

2

= 0

S

mn

response

Excitation

S 11 = Reflected

Incident =

b 1

a 1 a 2 = 0

S 21 = Transmitted

Incident =

b2

a 1 a 2 = 0

Input

reflection

Forward

transmission

Incident TransmittedS 21

S 11

Reflectedb 1

a 1

b 2

Matched

load Z0a 2 = 0

DUT

S21

S11

Gen

Forward

Z0

ZOUT

ZOUT=Z0



S

22

& S

1 2

S

mn

response

Excitation

IncidentTransmitted S 12

S 22

Reflected

b2

a 2

a 1 = 0

Z 0

Load

DUT

S12

S22

Gen

Reverse

S 22 = Reflected

Incident =

b 2

a 2 a 1 = 0

S 12 = Transmitted

Incident =

b1

a 2 a 1 = 0

Output reflection

coefficient

Reverse

transmission

Z0

ZIN

Matched load Z0 is fully

absorptive i. e. all wave is

taken by load and nothing

is given out i. e. a

1

= 0

Z0=ZIN



No. of Ports> 2

How to calculate S

1 1

?

S

n×n

n- port

Theory developed ca n be very well extended to devices ha ving more tha n two- ports

.

Termination

Termination

Termination

m

n

o

m

n

o

S

1 1

Properties of S- para meters ; See Mathew book; pp. 296- 299



S- parameters Properties

In general, S- parameters are with amplitude

and phase

Eq. 1 can be written in summation form as:

N ......,1,2, j , 1SS *

ij

N

1i

ij =

=

[ ] [ ]

[ ] [ ]

1T

T

SS

U SS

−

=

=

(1 )

And Lossless if:

S- matrix is reciproca l & symmetrical if:

S

1 2

= S

21

; S

1 1

= S

22



Cont..

Unity Property The sum of products of any column of [S] with the

conjugate of that column gives UNITY.

The sum of products of any row of [S] with the

conjugate of that row gives UNITY.

1SSSS * 21 21*1111 =

1SSSS *

22 22

*

1212 =

=

22 21

12 11

SSSSS

j all i forSS kj

N

k

ki ≠

=

,0*

1

Zero property:

The sum of products of any column of [S] with the

conjugate of a different column gives ‘ZERO’.

The sum of products of any row of [S] with the

conjugate of a different row gives ‘ZERO’.



Contd..

0SSSS *

22 21

*

1211 =

0SSSS *

21 22

*

1112 =

=

22 21

12 11

SS

SSS

=

0S S

S 0S

SS 0

S

32 31

23 21

1312

Write UNITY and ZERO expressions for

given S- matrix .

1SS 2

32

2

12 =

1SS 2

23

2

13 =

1SS

2

31

2

21 =

Unity

0

0

*

3231

*

3231

*

2221

*

1211

=

=

SS

SSSSSS

Zero



Ex:

8.56 Ω 8.56 Ω

141.8 Ω

Two port

Network

Z1 Z

2

Z3

Calculate S- parameters for the networks shown

50

Ω

GATE- 2007

With a2=0; calculate S

1 1

& S

21

/ ; / 022022 ZV b ZV a ii

−

= / ; / 011011 ZV b ZV a ii

−

=



Solution

S

22

= - 1 /3 ; S

1 2

=2/3

Follow similar procedure and calculate S22 S12

i1V

50 50

Z IN

V

i

1

−

i1V

-1/3 ZZ

ZZS

0IN

0IN

1

1

11

=

=

i

i IN

V

V

−

i2V

50 50

Z IN

V

i

1

i1V

i2V

3

2S

1

2

21 =

i

i

V

V



Solution

S

22

=0 ; S

1 2

=0 .71

Follow similar procedure

0

0

11 Z Z

Z ZS

IN

IN

=

Ω

+

50) //( 23

1

o

IN

Z Z Z

Z Z

0.011 =S

8.56 Ω 8.56 Ω

141.8 Ω Ω50

Two port

Network

Z1 Z

2

Z3

Z

IN

−i2Vi1V

i2V

3

2S

1

2

21 =

i

i

V

V

T ry fe w mor e e xe rc ises g iv en in Mathew Book



Alternative

Determine A, B, C, and D matrix for given network

+

−

+

D Z

C)ADZ

D

1

0

2

0

0

2

0

0

2

0

S

Use the conversion formula and determine S- parameters.

Network V1

V2

I1

I2

02

1

2=

=

I V

V A

02

1

2=

=

I V

I C

02

1

2=−

=

V I

I D

02

1

2=−

=

V I

V B



1V

1 I

2V

2 I 11 Z

212 I Z

+

−1 21 I Z

+

22 Z

−

2121111 I Z I Z V

+= 2 221 21 2 I Z I Z V

+=

Z- Parameters

(Background)

Z- parameter

circuit

LF< 1 GHz

For

calculating

performance

like:

A

V

Z

IN

etc.



1V 11Y 212V Y 1 21V Y 22Y 2V

2121111 V Y V Y I += 2 221 21 2 V Y V Y I +=

Y- parameter

circuit

LF< 1 GHz

For

calculating

performance

like:

A

V

Z

IN

etc.

Y- Parameters

(Background)



Question?

How the performances like A

V

, Z

IN

etc.

can be calculated for µwave

devices/circuits?

Convert S to circuit defin ing parameters like Z/Y/H S

Y

H

Z

Answer



Nomenclature

Frequencies above 20kHz acquire radiating

nature and they are terms as "Radio Frequency"

Various Bands

LF: 30- 300kHz ; MF: 300kHz- 3MHz

HF: 3- 30 MHz ; VHF: 30- 300MHz

UHF: 1 - 3GHz

SHF: 3- 30 GHz

EHF: 30- 300 GHz

µwave: 1 - 300GHz

λ: 30cm ~ 1mm

µwave



Unit-I:

µ

Wave

Components and Measurements

Guided Wave Propagation

Wave guide Components

Wave guide tuning, matching and loading

Directional coupler, Isolator, Circulator and Detector

Modeling of microwave components: S-parameters-----Finished

Measurements of microwave quantities

µ

waves

components and their working

Topics

Purpose



Guided Wave Propagation

Guided media, which provides a conduit from one

device to another includes: Wave guide, optical

fibers, tr. lines etc

They are hollow metallic tubes (rectangular or

circular) of uniform cross section for sending out

the

µ

waves

Waveguides

Rectangular

Circular

a

b

Waveguides are powerful media to

guide high power (KWs/MWs)µwaves

Their size are particularly

manageable in 3-100GHz range

Ref: Chapter 10 of Kennedy (4th ED) and Chapter 4 of Lio Book (3rd ED)



µwaves Propagation

Angle of incidence(A) Angle of reflection (B)

(A = B)f

µwaves propagate through successive reflections from the inner

walls of the guide

There are two modes of propagation: TE & TM

They are designated as TEmn or TMmn

Where m= no. of half- wave along x; n= no. of half- wave along y

TM: H is

⊥

to direction of propagationE: E is

⊥

to direction of propagation



Field

Distribution

=

a

x sin E E

y0 y

π

=

a

x cos H H

z0 z

π

=

a

x sin H H

x0 x

π

x

y

z

TE

1 H

H

H

H 2

x0

2

x

2

z0

2

z=

x

y z

E

Y

H

x

H

Z

A line model

x

y

z

a

b

H has

been

skipped out

due to

simplicity

TE Mode



Higher Mode

TE

30

a

x

y

z

E

20

a

b

Practice for

higher order

x

y

E

E- field

Half- wave

variation=02

x

y

E

E- field

half- wave

variation=03

H- field

x

z

H- field

x

z



TM Mode

Use M axwell’s equation to derive other field components

0 E E Z

2

Z

2

=

γ 0 E ;0 H Z Z ≠

Wave

Equation

TM: H is

⊥

to direction of propagation

z j

z0 z e y

b

n sin x

a

m sin E E −

=

Solution

+z direction

z

z

β

β

π

π

j

y0 y

j

x0 x

e b

y n sin

a

x m cos H H

e b

y n cos

a

x m sin H H

−

−

=

=

+z direction

a t x

b t y

z

z

=

=

Boundar

y

conditions

z

z

β

β

π

π

j

y0 y

j

x0 x

e b

y n cos

a

x m sin E E

e b

y n sin

a

x m cos E E

−

−

=

=

Page 112 of Lio Book

Field Distribution can be similarly Plot ted

If m= 0 or n= 0, the field intensities ALL vanish. So, there is NO , TM

01

or TM

1 0

.

TM

1 1

is the Lowest Mode

Try expressions for fc,

λ

g, vg ; See Lio Book; pp. 1 09 & 1 1 2 & Kennedy Book



GATE 2 7

H- field

x

z

x

y

z

E

20

a

b

x

y

E

E- field

No. of h alf-wave

variation=02

E- field in rectangular guide of dimension a

×

b is

given as:

z j

y e a

x K E ' 2

sin β

−

=

z

0 cossin β j

y y e b

y n

a

x m E E −

=

Compare the given expression with standard

expression

Ans: TE

20

mode

Determine the mode of propagation in the guide

Try questions: 4. 1 , 4. 4, 4. 5, 4. 1 2; See Lio Book;

pp. 1 61 - 1 62



Waveguide Components

Regulate Flow Of Power in

µ

wave System

Types

Hybrid Tee (Magic Tee)

Hybrid Rings (Rat- Race)

Corners, bends and twists- plane & H- plane Tees

Directional Couplers

Circulators and Isolators



A- B

A

- B

Difference

Sum

A+ B

A

B

How to Regulate?

Various Possibilities are:



Contd.

A

A/2

A/2

No

Unique

A

A/2

-A/2

qual half

(- )

A

A/2

A/2

qual half

(+ )



Study

Plan

Construction

How do they work?

Applications aspects

Wave guide Components



E & H-plane tees

These are the three port passive

devices

E-plane tee outputs are out of phase

H-plane tee outputs are in phase

Tees are used, when it is required to

combine two signals or split signal into

two parts in a µwave system

Ref: Kennedy Book; pp. 343-344 and Lio Book; pp. 144-146



Operation

Case-I: Feed in side arm

In

Out

Out

1

2

3

While passing

through the

junction, E-lines of

force bend as a

result of this, field

o f op po site p ola rity

emerge from t he two

main arms.

A

A/2

-A/2

F n . Dia gr am:

Outputs are equal but out of phase



Contd.

A/2+A/2 =A

A/2

A/2

3

21

A/2+A/2

A/2

A/2

Case-II: T wo feeds in main arm

Outputs (Sum)



H-plane tee—

Construction

An H-plane tee is

designed by

fastening a small

piece waveguide to

the narrow er arm of

the main waveguide

Side arm axis is

parallel to the

planes of H-field of

main guide

Side

arm

Main

arm

3

1 2



3

1

2

Operation

Reason Being…..

While passing through the junction (H-plane) the

E-field d oes not suffer any bending and consequently

th e ju nction split on e wav e in two equal h alf (in phase)

Case-I: Feed in side arm

Outputs are equal b ut in p ha se

A

A/2

A/2

F n . Dia gr am:



Contd.

.

Out

In

In

3

1

2

Case-II: T wo feeds in main arm

Outputs (Sum)



Hybrid tee

(Magic Tee)

4-port low loss passive device

Combined E-plane and H-plane tees

Power divided/combined among various

ports in peculiar way

Magic ≡ unusual manner

a

a/2

a/2

0

(

a+b)/2

a

b

(

a- b)/2

Power divided in Unusual way Power combined in Unusual way

Ex:



4

2 3

1

E-arm

H-arm

Hybrid tee (Magic

Tee)--Construction

H yb rid T ee = E+H t ee s

E-arm feed is not noticed

a t H -a rm a nd v ic e v er sa.



4

2

3

1

a/2

a

a/2

0

Operation

Wh y no output at ″4″ ?

No O/ P at "4"as side wall SHORT

The Wave

Case-I: Feed at Port 1

Half o/p at 2 and 3

(In Phase)

No O/P in

″

4

″

TE

1,0

operation assumed

a

x

y

z

″1″

E-field



4

2

3

1

a

-a/2

No

a/2

Contd..

Case-II: Feed in E - arm ″4″

O utputs are equal but

out of phase in ″2″ & ″3″

No O/P in ″1″

HW

No O/P at “1"as Broader wall

SHO RT The Wave

F n . D iagr am



4

2 3

1

a

b

Sum/2

Difference/2

E-

arm

H-

arm

Contd..

Case-III:

Feed in E- & H

both

″3″output (Sum)

″2″

output (Difference)

Hybrid

Tee

a

b

(a+b)/2

(a- b)/2

Fn . D iagr am



4

2 ,

1

a/2

a

No

a/2

Contd..

Hybrid

Tee

a

No

+a/2

+a/2



4

2 3

1

- a /2

a

No

a/2

Contd..

Hybrid

Tee

a

No

+a/2

-a/2

F n . D iagr am



Applications

Use for high power

applications

As a Mixer in RADAR receivers

Can be used to add two Tx

power to achieve higher range



Add 2-Tx Power

T

x1

T

x2

T

x2

+ T

x1

TeeS

T

x1

T

x2

T

x1

T

x2

T

x2

+ T

x1

2-Tx

powers

have

been

Added



Receiver Section

Mixer section in RADAR

Extreme ly high isolation between LO and received signal

What does

mixing means?

Difference of

two signals

Tx

LO

Hybrid Tee

Received Signal

Sum

F



Directional Coupler

A four-port passive low loss

device

Used to split some of the power of

main guide into secondary guide

Used for monitoring of the

RF/Microw ave pow er flow in main

guide line while introducing

minimum perturbation

Ref: Lio Book (3rd ED); pp. 149-154



Construction

λ/4

ThroughInput

Main waveguide

Auxiliary waveguide

21

43

Isolat ed

coupled

Slot/Cut

L=(2n+1)λ/4

Cancelled

DC

FDC BDC

FDC=Forward DC;

when feed is at 1

BDC=Backward DC;

when feed at 2



Signal Coupling

Signal gets coupled through

slot/cut/aperture and the

amount depends on size of cut

Slot/cut

Wave in

Wave out

Showing actual

mechanism



Symbol

Ex: T=Through 0.99Pin ; C=C oupled 0.01Pin ; I=Isolated 0.0

T = Most of the power ; C = Fraction of the power ; I = Almost no power

3

4

1

2

Pin

I

T

C



Working

1

3

2

4

C

Electronic Instrument

T

in

Added

Cancelled

Signals at ″C ″are added up constructively ; ″

C

″

collects ONLY 1%

of ″T″ due to sma ll cut (a perture)

Signals at

″

I

″

are added up destructively and NO output

appears 0.0



Slot/Cut

Signal gets coupled through

slot/cut/a perture and the a mount of

signa l coupled depends on size of cut

lot/cut

Wave in

Wave out

Showing actual

mechanism



FoM

×

=

3

4

4

1

3

1

P

P

P

P

P

P

4110 P Plog10C(dB) =

Coupling factor (C) - The ratio of input power to the coupled power

3 410 P Plog10 D(dB)=

Directivity (D)- The ratio forward power (coupled port ) to the

backward power (isolated port)

3110 P Plog10 I(dB)=

Isola tion factor (I) – The ratio of input power to power at the isolated port

C D I

Expressed

in dB

P erformance of DC is d ecid ed by C , D & I



With known value of ″C″

(manufacturer Supplied)

Application

(Pow er M onitoring)

A fraction of power measured

at

″

P

4

″

could Determine the

Main power

Try problem 4-26 of Lio Book (3rd ED); pp. 164-165



Hybrid rings

(Rat-Race )

Four port passive low loss device

Constructed from rectangular

guide but molded into circular

shape

Used in high power RADAR and

communications equipments



Construction

1

4

2

3λ/4

λ/4

λ

/4

λ/4

Looks

quite

different

from

magic tee

But

perform

very

similar to

magic tee

S hape is lik e a rin g

a/2

Fn. Diagram



4

2

3

3

λ

/4

λ

/4

λ

/4

λ

/4

a

a/2No

a/2

Operation

F eed in p or t

″

1

″

Output at ″4″ as

signals are added up

constructively

at given f

N o output at

″

3

″

as


destructively

at given f

Output at ″

2

″

as


constructively

at given f

Hybrid

rings

a

No

a/2

Power divides as uniquely as

in Magic Tee



W hy the name Rat-

Race?

O/P is the net

results of

two signal

races -- one

clockwise and

other in anti

clockwise

O/P



Application

4

2

3

3

λ

/4

λ

/4

λ

/4

λ/4

Tx

Antenna

No

Load

Tx Power is divided up into

Antenna & Load



Bends & Corners

Transition through the bend and corner are made gradually

to…….

…. Minimize reflection and loss of power

Bends &

Corners

θ

These components are used to ALTER the direction of the

wave by an arbitrary angle…

They are E- type, when bends along E- plane and H- type

when bends a long H- plane…



Bends

These components bend smoothly a long E or H- pla ne

E- bends bend along E- pla ne, wherea s H- bends along H- pla ne.

E- plane

bend

H- fields a re disturb as bend is

a long shorter wall

H- plane

bend

E- fields are disturb as bend

is a long broader wa ll

Bends are designed with radius r> 2

λ

……

…. . Minimize reflection



Corners

L=(2n+1)

λ

/4 n= 0, 1 , 2, 3, ……. to minimize reflection

Facilitates change along E- plane Facilitates change along H- plane

Purpose of corner is same as that of bend i. e. to change the

direction of the µ wave by an arbitrary angle

L

E- plane

corner

L

H- plane

corner

For the larger wavelength a bend is rather clumsy, and a corner is used

instead

Like Bends, Corners are also of E & H- type



Twists

Broader wall of guide

″

a

″

E

a

E

Bends/corners turns the wave direction without altering

E- field orientation.

E-field

E-field

Twists are used to a lter E- field orientation.

By what angle the E- field has been rotated? Ninety degree (90

0

)



µ

wave

source

Ex:

Bend

Bends used ALTER the direction of flow of wave

Probe

arrangement

µ

wave source: generates high frequency signal

Probe arrangement: for the purpose of monitoring of power flow



In µwave system, load reflects power and affects the generatorstability, in such scenario devices like Circulator & Isolator are usedbetween generator and load to improve the system stability

Generator

Load

R

L

Stability Issue

These are non-reciprocal passive µwave devices Improve the stability by providing unidirectional power flow




Symbol

3 4

1

4

3

2

1

2

3

4

Circulator

µwave circulator is a non-reciprocal Multi-port passive device Work on Sequential transmission, where input applied at port

″

n″

comes out at “next i.e. n+1 port″ but not out at ANY other port

3 4

Ref: Lio Book (3rd

ED); pp. 158-161



Sequential Flow

3

4

2

1



Working

Signal transferred from 1 to 2

but not from 2 to 1

1

2

1

2

4

3

From 1 to 2 : R= 0 but from

2 to 1 ; R=

∞



1

4

3

2 2 3

Signal transferred from 2 to 3

but not from 3 to 2



1

4

3

2

3 4

Signal transferred from 3 to 4 but not

from 4 to 3



1

4

3

2 1 4

Signal transferred from 4 to 1 but

not from 1 to 4



Circulator with N=3

1 2 3 1

HW

a signal applied to port 1 only comes out of port 2; a signal

applied to port 2 only comes out of port 3; a signal applied to

port 3 only comes out of port 1



Applications

Signal transmission: Tx power goes to antenna

Antenna

Tx

Load

Rx

Tx



Signal Reception

Antenna power goes to receiver

Antenna

Tx

Load

Rx

Rx

Tx & Rx connected to a single antenna have been isolated



(Example showing

use

of both DC and circulator)

Ex:

Performance

assessment

Load

enerator

Power is being made available at input of DC

using circulator

Using C port of DC, spectrum analyzer and

oscilloscope a re connected to MON ITER the flow

of power in the system

Determine the S- parameters of 3- port circulator shown.

S



2

1

3

0&1

221

302 =

=

a a a

bS

50

Ω

50Ω

S

1 1

= S

22

= S

33

= 0

2

1

3

50Ω

0&2

332

301 =

=

a a a

bS

Assume that ports a re matched

Excitation

esponse

mn

S

mn



Excitation

esponse

2

1

3

0Ω

50

Ω

0&3

113

201 =

=

a a a

bS

=

0 1 0

0 0 1

1 0 0

S

Final result

S

mn

Determine the S- parameters of 3- port circulator

shown. Assume that ports are matched



2

1

3

1

0

312312

133221

=

=

SSS

SSS

0&2

112

301 =

=

a a a

bS

0&3

223

201 =

=

a a a bS

0&1

331

302 =

=

a a a

b

S

=

0 0 1

1 0 0

0 1 0

S

Excitation

esponse

HW

S

1 1

= S

22

= S

33

= 0



Isolator

Isolator is a 2-port passive

device

Allows one way flow of power

in µwave system

Improve the stability of

µ

wave

generator




L

E

E

×

×

×

×

×

×

×

×

×

×

×

θ

H

Working

Angle of rotation

θ

depends on:

length of ferrite rod

diameter of rod

strength of applied magnetic field

strength “H”

Ferrite rod

Works on the concept of Faraday Rotation

Ferrite rod could be designed to make θ= 45

0

When e. m. waves are launched through some specia l ferrite

materia l, then their pola rization is rotated by an angle θ

These materia ls are Magnese Ferrite (MnFe2O3), Zinc Ferrite (ZnFe2O3)

ISOLATOR



x

y

z

E

E

E

E

Lossy vane

Ferrite rod

H

Lossy vane

I/P

Output waveguide

1

2

Input waveguide

O/P

Load

Lossy vane

Coated with carbon

material; wave gets along

when ⊥ a nd lost when

1

2

R= 0

: How signal is transferred from 1 to 2?



x

y

z

E

E

E

E

Lossy vane

Ferrite rod

H

Lossy vane

I/P

Output waveguide

1

2

Input waveguide

O/P

Isolator

Load

1

2

R= 0

Field propagates

as E is

⊥

to lossy

vane

E is rotated

by 45

0

Vane is also rotated by

45

0

thus making as E

⊥

to resistive vane

Waveguide

rotated as well

by 45

0

to

facilitates the

wave flow

Finally wave

collected at load

Generator feeds

in power

As reverse signa l is a ligned to lossy va ne

and no signa l rea ch to the genera tor



x

y

z

Lossy vane

Ferrite rod

H

Lossy vane

Input waveguide

Output waveguide

Load

1

2

ref wave

ref wave—add 45

0

ref wave—LOST

No signal transfer from 2 to 1

1

2

=∞

Reflected wave get

in to O/P guide

Ferrites rod further

rotate the wave by

an angle of 45

0

E now become parallel

to vane and get LOST

All waves are not

collected a nd some of

them a re ref ba ck

ref waves do not

reach the Gen

These devices have Loss

1 dB and Isola tion

40dB



W hat Next?

Learn the Concepts Matching and Load in

context with Wave Guide System >1Ghz)

Impedance Matching is a technique through which

circuit/device impedance level is appropriately

altered to ensure better flow of power

MN is quite often rea lized using LOSSLESS L & C Components

Z

0

Z

L

Z

L

collect less power; Z

L

≠

Z

0

Tr. line with Z0

Z

0

Z

L

&C

Matching Network (MN)

Z

L

collects

more power

Tr. Line with Z

0

Ex:

Ref: Kennedy Book (4

th

Ed.) ; pp.

347- 352



Ex:

If Z

L

= Z

0

, then N O r eflection occurs ----Ideal line with NO

loss of power



Standing w ave pattern results w hen Z

L

≠ Z

0

--- N ot m atched

a nd p ow er loss d oe s o cc ur

Ex:

Standingwave



W aveguide System

Like transmission line, wave guide systems (> 1 GHz) are to be

impedance matched to the loads………in order to minimize

reflection

For frequency < 1 GHz, matching elements are realized using

lumped L & C……

How these elements (L& C) are realized at µwave (> 1 GHz)?

These are rea lized using wave guide components ca lled ″IRIS″



IRIS

Wave

guide

′C ′ is realized

The obstacle (IRIS), which a lter E- field w ill rea lize capacitance.

″

C

″

obta ined is related with the size of obstacle

C



Types

Unsymmetrical

Centrally

located

Symmetrica

l

Evenly

located

Both configurations will realize

″

C

″

C



Fixed Type

Attenuation (dB)= 10*log(P

in

/ P

out

)

Output wave, P

OUT

Input wave, P

IN

Coating of

Aquadag

Reduce wave power by a fixed amount

Aquadag ≡ Glass coated with carbon

R

Variable Type



Input wave

Output wave

Pivot

Carbon

Flap

Attenuation a s high as

∼

80dB could be realized through techniques

Carbon flap descend into the guide is adjustable (variable)

Wave power reduced can be adjusted

R

W aveguide Loads



Taper edge gives rise gradua l impedance transition and reduced reflection

Load is similar to attenuator but normally kept at the end of guide

If tapered on both the ends, then it called double tapered (DT)

Load depends on dielectric of lossy materia l used

R

≈ 2λ

≈ λ/2

Lossy

material

Single

tapered



Basic rules

Know which quantity you wish to measure

Proper test arrangement i. e. equipments

required

sources: oscillator…. .

detectors: power meter, spectrum analyzer, network

analyzer…. .

auxiliary devices: attenuator, directional coupler…. .

Should be familiar with how to carry out a

particular experiment

Learn how to interpret various results

Take appropriate precaution due to high

frequency involved



Types



Sensor Techniques

Calorimeter

Bolometer

Thermocouple

Themistor

NTC (-

R)

Barreter

PTC (+

R)

Measure (+

T)

Measure (

±

V )

Measure (

±

R )

NTC e.g. thermister & PTC e.g. barreter

Thermistor → Meta l oxide of

Ni, Mn, Co etc.

Baretter →

Metal like

platinum etc.



Calorimeter

Used for high power

Work on absorption of microwave

power by fluid usually water

Measure the rise in temperature of

the fluid due to absorption of

rf/microwave power

Poor response time

Less accurate



Bolometer

Temperature sensor resistor

Work on bridge circuit concept

Used to measure low power (< 1 mW)

Higher accuracy

Better sensitivity

Faster response time



Working



First ba lanced the bridge

Apply

µ

wave power to one arm of

the bridge

record the potential difference, which is

corresponding to change in resistance

R

R can be calibrated to measure

µwave powers

P

ABC

Calibration

curve



Working

Temperature difference at junctions induce

potentia l difference ( v) proportiona l to absorbed

power (P

ABC

) i. e. P

ABS

∝ v

Difference in voltage generated can be ca librated

to measure

µ

wave power

v

P

ABC

Calibration

curve

VSWR

MAX V

MIN V



VSWR gives

measure of

degree of

mismatch on line,

which manifests

in terms of SWP

Standing wave

pattern results

when Z

L

≠

Z

0

, and

it indicates power

loss

VSWR at

µ

wave

is measured using

SLOTTED LINE

=

MIN

MAX

V

V VSWR

(Concept)

SWP

L ZO Z

Slotted Line

An arrangement to sample wave on SWP



It includes:

Sliding base fitted with probe to sample wave on Waveguide/Tr. line system ---- then sampled wave value is measured through µmeter.

Slotted Line

Fn. Diagram

E- probe

SWP

µmeter

Waveguide

Load

Outcome of pink and

green waves

enerator

Incident power

Reflected power



Wavelength



)(22

21

21

x x

x x

−

−

λ

λ

x

1

= first minima

x

2

= next consecutive

minima

Sample 2- consecutive

minima using sliding

probe and determine

λ

Similar set up like VSWR can be used to measure

λ

measuredis

Set up with sca le attached

µmeter

λ/2 SWP



Theory. .



=

2

1log10 P P IL

IL is the characteristics of DUT used

If DUT input port is matched, then P

4

= 0, then Return Loss (RL)

=Attenuation Loss (AL)

−

−

=

−

×

− 41

1

2

41

2

41

41

1 log10log10log10 P P

P

P

P P

P

P P

P P

P IL

IL

RL

AL

Let us develop set up for AL & RL

RLALIL +

Set up for AL



Loada2=0DC1

DUT

DC3

BolometerP1

SignalGenerator

Bolometer

P2C2

Bolometer

P4

−

= 2

41

P

P P

AL

Measure

feed power

Measure

reflected

power

Measure

transmitted

over power

It Includes:

DC, Bolometer etc.



Concluding Remarks



Fundamentals about µwaves were covered

Various

µ

wave components and their working

were taken up

Set up to measure

µ

wave quantities of

interest were explained

Question?



IRIS

Wave

guide

C L

What is realized by the IRIS arrangement shown? Assume TE

1 , 0

mode

microwave unit 1

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