4ece mw networks

7/31/2019 4ece MW Networks

1/79

MICROWAVE NETWORKS

Dr L.Anjaneyulu

NIT, Warangal

[email protected]


2/79


3/79

Network ports

What is the difference between the port of

low frequency network and microwave

frequency network ?

For low frequency network a port is a pair

of terminals where as for a microwave

network a port is reference planetransverse to the length of microwave

transmission line


4/79

Network Parameters

Z, h, Y and ABCD parameters are difficultto measure for microwave networkbecause at microwave frequencies the

physical length of the component or line iscomparable to or much greater than thewavelength.

so the voltage and current are not welldefined at a given point for a microwavecircuit


5/79

Why Z, Y,h and ABCD parameters are

difficult to measure for MW circuit ?

1) Non- availability of terminal voltage and

current measuring equipment

2) Short circuit and open circuits are not

easily achieved for a wide range of

frequencies

3) Presence of active devices makes the

circuit unsuitable for short and open circuit


6/79


7/79


8/79

A photograph of the Hewlett-

Packard HP8510B Network

Analyzer. This test instrument

is used to measure the

scattering parameters

(magnitude and phase) of a

one- or two-port microwave

network from 0.05 GHz to

26.5 GHz. Built-in

microprocessors provideerror correction, a high

degree of accuracy, and a

wide choice of display

formats. This analyzer can

also perform a fast Fourier

transform of the frequencydomain data to provide a time

domain response of the

network under test.

Courtesy of Agilent

Technologies.


9/79


10/79


11/79


12/79


13/79


14/79


15/79


16/79


17/79


18/79


19/79


20/79


21/79


22/79

Properties of S - Parameters

a) Zero diagonal elements for perfectmatched network

For an ideal N-port network with matchedtermination sii= 0 since there is no reflectionfrom any port

so under perfect patched conditions thediagonal elements of [S] are zero


23/79

Properties .

b) Symmetry of [S] for a reciprocal network

A reciprocal device has the same

transmission characteristics in eitherdirection of a pair of ports ischaracerized by a symmetric matrix

Sij = Sji ( i not equal to j)


24/79

Properties

c)Unitary property for a lossless junctionFor any lossless network the sum of theproducts of each term of any row or of any

column of the S matrix multiplied by itsconjugate is unity

If all


25/79


26/79

Phase shift property

Device S

1 1 2 2

2221

1211

SS

SSS

Complex S-parameters of anetwork defined with respect tothe positions of the port orreference planes

For unprimed reference planes the Sparameters havedefinite complex values


27/79

Phase shift property cont..

222

111

l

l

Device S

1 1 2 2

If reference planes 1 and 2are shifted outward to 1and 2 by electrical phase

shifts

2

1

2

1

0

0

0

0'

j

j

j

j

e

eS

e

eS

The new S matrix is given by


28/79


29/79


30/79


31/79


32/79


33/79


34/79


35/79


36/79


37/79


38/79


39/79


40/79

Several Losses in Microwave

circuits

The losses in a microwave circuit can be

expressed in terms of S-parameters

Insertion Loss

(dB)

Pi = Power fed at Port 1; Pr = Power reflected at the same port


41/79

Losses

Transmission Loss

or Attenuation (dB)

Reflection Loss

(dB)


42/79

Losses ..

Return Loss (dB)


43/79

S parameters for some microwave

components


44/79

Wave guide sections

01

10S

The S-Matrix for

ideal sections are

Examples of S matrices: 2-ports (1)


45/79

Bends


46/79

Adopters

Between series adapter (WR-51 to WR-42)

Waveguide to coax adapter

(WR-62 to type N)


47/79

Flexguide (non-twistable)


48/79



49/79



50/79


51/79

S Matrix for Wave guide - Tees

Wave guide tees are three port

components. They are used to

connect a branch or sections of the

waveguide in series or parallel with

the main waveguide transmission line

for providing means of splitting andalso of combining power in a

waveguide system


52/79

Two basic types of Tees

E-plane T H-plane T

S t f E l d H


53/79

S-parameters of E-plane and H-

plane -T

E-plane H-plane

Because of the

symmetry Sij = Sjij = 1.2

332313

231112

131211

SSS

SSS

SSS

S


54/79

E l T


55/79

E-plane T

S31 = S13= - S23 = -S32

S12=S21

ai = incident power

bi = reflected power

02/12/1

2/12/12/1

2/12/12/1

2

13

2

33 2)1( SS If S33 =0 ,S13 = 1/ 2

I/p power =o/p power


56/79

H-plane Tee

In a H-plane tee if two waves arefed into port 1 and port 2 of thecollinear arms the output wave atport 3 will be in phase andadditive.

Reversely an input wave at port 3 will be equally divided into port1and port 2 in phase.

02/12/1

2/12/12/1

2/12/12/1

S


57/79


58/79

Hybrid -T


59/79


60/79

Cross guide couplers


61/79

Directional Coupler

The coupling factor is defined as:
http://en.wikipedia.org/wiki/Image:6-4ep2.gifhttp://en.wikipedia.org/wiki/Image:6-4ep2.gif


62/79

S-parameters of DC

Insertion Loss (IL) = 10*log(P1/P2)=-

20*log(S21)

Coupling Factor (CF) = 10*log(P1/P4)=-

20*log(S41)

Isolation (I) = 10*log(P1/P3) = -20*log(S31)

Directivity (D) = 10*log(P4/P3)=-

20*log(S31/S41)


63/79

DC

COUPLERS


64/79

COUPLERS

0 1 1 0

1 0 0 1.

1 0 0 12

0 1 1 0

jS

0 1 0

0 0 111 0 02

0 1 0

,

j

jSj

j

The quadrature hybrid (or branch-line hybrid) is

a 3 dB coupler. The quadrature term comesfrom the 90 deg phase difference between the

outputs at ports 2 and 3.

The coupling and insertion loss are both equal

to 3 dB.

Ring hybrid (or rat-race) couplerQuadrature hybrid Coupler

A microwave signal fed at port 1 will split evenly

in both directions, giving identical signals out of

ports 2 and 3. But the split signals are 180 deg

out of phase at port 4, the isolated port, so they

cancel and no power exits port 4.

The insertion loss and coupling are both equal to

3 dB. Not only can the ring hybrid split power to

two ports, but it can add and subtract a pair of

signals.

Filters


65/79

Filters

Filters are two-port networks used to attenuate undesirable frequencies.

Microwave filters are commonly used in transceiver circuits.

The four basic filter types are low-pass, high-pass, bandpass and bandstop.

Low-pass High-pass

BandstopBandpass

Filters


66/79

A low-pass filter is characterized by the insertion loss

versus frequency plot in Figure. Notice that there may

be ripple in the passband (the frequency rangedesired to pass through the filter), and a roll offin

transmission above the cutoff or corner frequency, fc.

Simple filters (like series inductors or shunt capacitors)

feature 20 dB/decade roll off. Sharper roll off is

available using active filters or multisection filters.

Active filters employ operational amplifiers that arelimited by performance to the lower RF frequencies.

Multisection filters use passive components (inductors

and capacitors), to achieve filtering.

The two primary types are the Butterworth and the

Chebyshev. A Butterworth filter has no ripple in the

passband, while the Chebyshev filter features sharperroll off.

Low-pass Filters

Lumped Element Filters


67/79

Low-pass Filters

High-pass Filters Band-pass Filters

p

Some simple lumped element filter circuits are shown below.



68/79

Low-pass Filter Example

p

2

,l

L

o

v

PR

.2

o

l s

o

R

v vR j L

20log 1 .2

o

j LIL

R

The 3 dB cutoff frequency, also termed the corner frequency, occurs where

insertion loss reaches 3 dB.

1,2

o

L

R

20log 1

23

o

j L

R

3

201 10 22

o

j L

R

.oc

Rf

L

2

2 22

.4

s

l s

A

o o o

v

v vP

R R R

10log L

A

ILP

P

Power delivered to the load

Insertion Loss

Maximum available Power:



69/79

Low-pass Filter Example

Example 10.12: Let us design a low-pass filter for a 50.0 system using a

series inductor. The 3 dB cutoff frequency is specified as 1.00 GHz.

p

.oc

Rf

L

The 3 dB cutoff frequency is given by

950

15.9 .1 10 1

oR H

L nHf sx s

Therefore, the required inductance value is

Filters


70/79

The insertion loss for a bandpass filter is shown in

Figure. Here the passband ripple is desired small.

The sharpness of the filter response is given by theshape factor, SF, related to the filter bandwidth at 3dB

and 60dB by

60

3

.dB

dB

BWSF

BW

A filters insertion loss relates the power delivered to

the load without the filter in place (PL) to the power

delivered with the filter in place (PLf):

10log .L

Lf

PIL

P

Band-pass Filters

Amplifier Design


71/79

p g

Microwave amplifiers are a common and crucial component of wireless transceivers.

They are constructed around a microwave transistor from the field effect transistor

(FET) or bipolar junction transistor (BJT) families.A general microwave amplifier can be represented by the 2-port S-matrix network

between a pair of impedance-matching networks as shown in the Figure below. The

matching networks are necessary to minimize reflections seen by the source and to

maximize power to the output.


72/79


73/79


74/79


75/79


76/79

Example : Output Matching Network


77/79

Step 1: Plot the reflection coefficient

Step 3:Intersection points on 1+jb Circle

Step 4:Open-Circuited Stub Length

Step 2: Find the Admittance yL

Shunt Stub Problem:

Admittance Calculation

61876.0L

L

1

2

3

4

3

4

2 3 4

Example : Input Matching Network234


78/79

Step 1: Plot the reflection coefficient

Step 3:Intersection points on 1+jb Circle

Step 4:Open-Circuited Stub Length

Step 2: Find the Admittance ys

1

2

3

4Shunt Stub Problem:Admittance Calculation

120.01 d

5.311 jy

206.01

123872.0s

S

X

Ignore

Treat as a load

234


79/79

4ece mw networks

Documents