Chapter 1 part 2 - UniMAP Portalportal.unimap.edu.my/portal/page/portal30/Lecturer Notes... ·...

MICROWAVE ENGINEERINGChapter 1 (Part 2)

EKT 345

1.3 Microwave Components

1. Directional Couplers

2. Detectors

3. Mixers

4. Quadrature hybrids

5. Circulators and isolators

6. Attenuators

7. Power dividers

8. Filters

9. Antennas

1.3.1 Directional Coupler

� A component which allows two microwave circuits to be combined

into one integrated system in one direction, while being completely

isolated from each other in opposite direction.

Cont’d…

http://www.asia.ru/en/ProductInfo/1140822.html

www.aptecelectronics.com

Cont’d…

Cont’d…

� dual directional coupler

� Monitor forward and

reflected power at the

same time

� Obtaining data from a

device indicates the input

match

1.3.2 Detectors

� Reliable, trouble free system

� heart of detector – diode

� Obtain maximum power transferred

� Filter – eliminate high frequency

ripple, allow dc at the output

www.hitechtech.com

www.anritsu.com

Cont’d…

� Detector sensitivity curve

� RF power applied to the

detector’s input, another is the

DC output voltage.

� The DC voltage produced at the

output for a specific power

input – how much power

required to produce

certain voltage

Cont’d…

� To control or to convert an RF signal to a DC

voltage for display purposes.

� Others

� Monitoring an RF line

� Leveled power – swept measurement

� View signals at certain frequencies:

�Eg: above 100MHz

Cont’d…

Cont’d…

1.3.3 Mixers

� The frequencies is not the

one needed – too low or

too high

� To produce new

frequencies

Cont’d…

� Configurations:

a. Single diode mixer

b. Balance diode mixer

c. Image rejection mixer

Cont’d…

� Applications

� a receiver front end

� an up-converter in a transmitter

� a balanced modulator

� down convert signal for NF measurement

1.3.4 Quadrature Hybrids

� a directional coupler whose two outputs equal in amplitude and separated from one another by a constant 90º phase.

http://www.webstore.com/T2OT6-Narda-Microwave-4035

http://www.rfglobalnet.com/doc.mvc

Cont’d…

�Applications

� Mixer

� Matched detector

� RF and DC combination

� Combining amplifiers

� SPDT pin switch

1.3.5 Circulators and

isolators

� Both use the unique

properties of ferrites in a

magnetic field

� Isolator passes signals in

one direction, attenuates

in the other

� Circulator passes input

from each port to the next

around the circle, not to

any other port

Circulator illustration

Cont’d…

www.saisum.com

www.made-in-china.com

Cont’d…

Circulator construction

1.3.6 Attenuators

� To less the value

� To diminish the power of a

signal while keeping the

waveform of the signal intact.

An attenuator introduces a

known amount of loss when

functioning between two

resistive impedances: Input

Impedance, Zin and Output

Impedance, Zout

� Fixed, variable and pin

attenuators

http://article.wn.com

Cont’d…

� Fixed attenuators

� Use in reducing voltage and in dissipating power

� Use in improving impedance matching

� Temperature compensation

� Measuring gain/loss of a device

Cont’d…

� Variable attenuators

� Continuously attenuators

� Piston, variable card, T, variable coupler, low-loss

cut-off, lossy wall

� step attenuators

� pin attenuators

� Variable attenuator that provides either step or

continuous attenuation without the use of piston

etc – use pin diode

� Attenuation – this amount that by which the

input signal is decreased when the pin diodes are

fully biased (maximum current drawn)