1

SCHOOL OF COMPUTER &COMMUNICATIONS ENGINEERING

 

EKT 341/4 ANTENNAS AND PROPAGATION

Lecturer:En. Rosmizi bin Abd RahimDr. Mohd Faizal Bin Jamlos

PLV:Puan Hazila Othman

2

Marks allocation:

Final Exam : 50%Written Tests : 20%Mini Project : 10%

Laboratory : 15%Quiz, Assignment & others : 5%

3

Introduction

Agilent Technologies offers a wide range of both scalar and vector network analyzers for characterizing components from DC to 110 GHz. These instruments are available with a wide range of options to simplify testing in both laboratory and production environments.

Network Analyzer

4

Types of Network AnalyzerScalar• Magnitude only

• Broadband Detector with higher noise floor

• Lower Price

• Normalization – Less Accurate

• Measures RL, SWR, Gain/Loss

Vector• Phase and Magnitude

• Tuned Detector with lower noise floor

• Higher Price

• Complete Error Correction – More Accurate

• Measures all

5

Network Analyzers Vs Spectrum Analyzers .

Am

plit

ude

Rat

io

Frequency

Am

plit

ude

Frequency

8563A

SPECTRUM ANALYZER 9 kHz - 26.5 GHz

Measures known signal

Measures unknown signals

Network analyzers: measure components, devices,

circuits, sub-assemblies contain source and receiver display ratioed amplitude and

phase(frequency or power sweeps)

offer advanced error correction

Spectrum analyzers: measure signal amplitude characteristics

carrier level, sidebands, harmonics...) can demodulate (& measure) complex signals are receivers only (single channel) can be used for scalar component test (nophase) with tracking gen. or ext. source(s)

6

Why Use S-Parameters?

relatively easy to obtain at high frequencies hard to measure total voltage & current at the device ports at high

frequency measure voltage traveling waves with a vector network analyzer don't need shorts/opens which can cause active devices to oscillate or

self-destruct relate to familiar measurements (gain, loss, reflection coefficient ...) for RF design, S-parameters are easily imported and used for circuit

simulations in electronic-design automation (EDA) tools like Agilent's Advanced Design System (ADS). S-parameters are the shared language between simulation and measurement.

Vector Network Analyzer 7

Measuring S-Parameters

S 11 = Reflected

Incident=

b1

a 1 a2 =0

S 21 =Transmitted

Incident=

b2

a 1 a2 =0

S 22 = Reflected

Incident=

b2

a 2 a1 =0

S 12 =Transmitted

Incident=

b1

a 2 a1 =0

Incident

TransmittedS

21

S11

Reflectedb1

a1

b2

Z0

Loada2 =0

DUTForward

Incident

Transmitted S

12

S22

Reflected

b2

a2b

a1=0

DUTZ0

Load Reverse

1

8

Basic Antenna Parameters

Antenna Parameters 9

• Radiation Pattern

• Input Impedance and Impedance Matching

• Return Loss / Reflection Coefficient ?

• Bandwidth

• VSWR

•Demo

10

HPBW (3dB Beamwidth) : The half power beamwidth (HPBW) can be defined as the angle subtended by the half power points of the main lobe.

Main Lobe: This is the radiation lobe containing the direction of maximum radiation.

Minor Lobe:All the lobes other then the mainlobe are called the minor lobes. These lobes represent the radiation in undesired directions.

Back Lobe: This is the minor lobe diametrically opposite the main lobe.

Side Lobes: These are the minor lobes adjacent to the main lobe and are separated by various nulls. Side lobes are generally the largest among the minor lobes.

***In most wireless systems, minor lobes are undesired. Hence a good antenna design should minimize the minor lobes.

Antenna Parameters

11

The input impedance of an antenna is defined as “the impedance presented by an antenna at its terminals or the ratio of the voltage to the current at the pair of terminals ”.

An ideal antenna solution has an impedance of 50 ohm all the way from the transceiver to the antenna.

Hence the impedance of the antenna can be written as:

where

Antenna Parameters

12

Smith Chart Review

Z = ZoL

= 0

Constant X

Constant R

Smith chart

LZ = 0

=±180 O1

(short) Z = L

= 0 O

1

(open)

Antenna Parameters

13

The Return Loss (RL) is a parameter which indicates the amount of power that is “lost” to the load and does not return as a reflection.

RL is a parameter similar to the VSWR to indicate how wellthe matching between the transmitter and antenna has taken place.

The RL is given as :

For perfect matching between the transmitter and the antenna,Γ = 0 and RL = ∞ which means no power would be reflected back, whereas a Γ = 1 has a RL = 0 dB, which implies that all incident power is reflected.

Return Loss (RL)

14

Return Loss (RL)

Return Loss

A very good antenna might have a value of -10dB (90

% absorbed & 10 % reflected).

15

BandwidthThe range of frequencies on either side of the center frequency where the antenna characteristics like input impedance, radiation pattern, beamwidth, polarization, side lobe level or gain, are close to those values which have been obtained at the center frequency.

The bandwidth of a broadband antenna can be defined as the ratio of the upper to lower frequencies of acceptable operation.

The bandwidth of a narrowband antenna can be defined as the percentage of the frequency difference over the center frequency.

The equations as follows:

Antenna Parameters

16

Bandwidth

Bandwidth (BW) can be

measured by looking at the

frequency range where

reflection coefficient value

dropped below than -10 dB.

Antenna Parameters

Antenna Parameters 17

VSWRVSWR is a measure of impedance mismatch between the transmitter and the antenna. The higher the VSWR, the greater the mismatch. The minimum VSWR, i.e., that which corresponds to a perfect impedance match, is unity.

The result is presented as a figure

describing the power absorption

of the antenna. A value of 2.0:1

VSWR, which is equal to 90 %

power absorption, is considered

very good for a small antenna.

Vector Network Analyzer 18

Vertical Position

Horizontal Position

Half Wave Dipole Antenna

hazila_2010

Radiation Pattern

Vector Network Analyzer 20

Radiation Pattern

Yagi Antenna

Vector Network Analyzer 21

THE END