WAVE PROPAGATION AND ANTENNAS Introduction

ANTENNA DEFINITION

• Webster’s Dictionary: “a usually metallic device (as a rod or wire)

for radiating or receiving radio waves.”

• The IEEE Standard Definitions of Terms for Antennas (IEEE Std 145–
1983): defines the antenna or aerial as “a means for radiating or
receiving radio waves”
 ANTENNA SYSTEM

• Source èwaveguide/transmission line è Antenna

è Propagation through free space
ANTENNA EQUIVALENT
CIRCUIT MODEL
• ZC = transmission line impedance

ZC
• ZA = Antenna Impedance

• Rr = radiation resistance

• RL = Load resistance

• XA = Antenna reactance

• Zg= internal source resistance

TYPE OF ANTENNAS
Wire Aperture

Microstrip
TYPE OF ANTENNAS
Reflector Lens
 Array

TYPE OF ANTENNAS
 TYPE OF ANTENNAS
Second Largest reflector antenna Largest reflector antenna
Puerto Rico – 305 m diameter China – 500 m diameter
 CAUSE OF RADIATION
1. If a charge is not moving, current is not created and there is no
radiation.
2. If charge is moving with a uniform velocity:
a. There is no radiation if the wire is straight, and infinite in extent.
b. There is radiation if the wire is curved, bent, discontinuous,
terminated, or truncated.
3. If charge is oscillating in a time-motion, it radiates even if the wire
is straight.
 CAUSE OF RADIATION
1. If a charge is not moving, current is not created and there is no
radiation.
2. If charge is moving with a uniform velocity:
a. There is no radiation if the wire is straight, and infinite in extent.
b. There is radiation if the wire is curved, bent, discontinuous,
terminated, or truncated.
3. If charge is oscillating in a time-motion, it radiates even if the wire
is straight.
WAVE PROPAGATION AND ANTENNAS Introduction
 TWO WIRES

• A voltage source is connected to two wires

• Electric fields are created

• Waves are detached such as water droplet in a pond

 DO WE NEED CONTINUES CHARGES TO
SUSTAIN THE FIELDS?

Electric charges are required to excite the fields

but are not needed to sustain them and may
exist in their absence.
 DIPOLE ANTENNA

• If the spacing between the wires S<<λ è

fields are cancelled

• Once flared the fields are not cancelled

è radiation
TRANSMISSION LINES
The standing Eave Ratio is given by:

Propagating wave Vs. Standing wave

Propagating wave Standing wave

CURRENT DISTRIBUTION OF A DIPOLE
 HISTORICAL ADVANCEMENT

Please read section 1.5 page 20 of the book for the

historical development of antennas
WAVE PROPAGATION AND ANTENNAS Fundamental Parameters
RADIATION PATTERN

• “a mathematical function or a graphical

representation of the radiation properties
of the antenna as a function of space
coordinates”

• In the far field region

• Field pattern/power pattern

LINEAR/LOGARITHMIC SCALE

HPBW = Half Power Beamwidth

 RADIATION PATTERN LOBES

• Major lobe/ Main lobe

• Minor lobe

• Side lobe

• Back lobe
ISOTROPIC ANTENNA PATTERN
ANTENNA PATTERN
Omnidirectional Directional
EXAMPLE OF A 10 ISOTROPIC ELEMENT ANTENNA
 FIELD REGIONS

1. Reactive near-field
2. Radiating near-field (Fresnel)
3. Far-field (Fraunhofer) regions

D is the largest dimension of the antenna

FIELD REGIONS
 RADIAN/STERADIAN
• One radian = “the plane angle with its vertex at the center of a
circle of radius r that is subtended by an arc whose length is r”

• The circumference of a circle of radius r is C = 2πr, there are 2π

rad (2πr/r) in a full circle.

• The measure of a solid angle is a steradian.

• One steradian = the solid angle with its vertex at the center of a
sphere of radius r that is subtended by a spherical surface area
equal to that of a square with each side of length r.

• The area of a sphere of radius r is A = 4πr2, there are 4π sr

(4πr2/r2) in a closed sphere.
RADIATION POWER DENSITY
 RADIATION INTENSITY

Radiation Intensity = the power radiated

from an antenna per unit solid angle
 SIMULATION EXERCISE
1) Find the input impedance of the dipole, when the source impedance is:
a) 70 ohms
b) 30 ohms

2) Change the frequency range from 0.5 GHz to 30 GHz, then:

a)Plot the S11

b))find the frequencies that corresponds to purely resistive input impedance
c) change the source impedance Zs to the impedance found in part (b) and plot the S11.
d) Compare the S11 results found in (a) and (c). Discuss the findings with your group members.
WAVE PROPAGATION AND ANTENNAS Fundamental Parameters
 BEAMWIDTH
• The beamwidth = “the angular separation between
two identical points on opposite side of the pattern
maximum”

• HPBW = Half Power Beamwidth

• FNBW = First Null Beamwidth

• When the beamwidth The side lobes

 DIRECTIVITY
• The ratio of the radiation intensity in a given direction from
the antenna to the radiation intensity averaged over all
directions
• it is a measure that takes into account the directional
capability of the antenna
 ANTENNA EFFICIENCY

e0 = total efficiency (dimensionless)

er = reflection(mismatch) efficiency = (1 − |Γ|2)(dimensionless)
ec = conduction efficiency (dimensionless)
ed = dielectric efficiency (dimensionless)
 GAIN
Gain è It accounts for the losses due to the antenna only (ec
and ed) and assume the mismatch loss = 0.
the ratio of the intensity, in a given direction, to the
radiation intensity that would be obtained if the
power accepted by the antenna were radiated
isotopically.

it is a measure that takes into account the efficiency

Absolute Gain è it counts for all losses including the mismatch
of the antenna as well as its directional capabilities
losses
 BANDWIDTH

the range of frequencies within which the

performance of the antenna, with respect to some
characteristic, conforms to a specified standard.

Narrow band antennas è expressed as percentage

from center frequency

(fmax + fmin)/2
 BANDWIDTH

Wide band antennas è expressed as the ratio of

upper frequency to lower frequency

E.G of upper freq = 12 GHz

Lower Freq = 1 GHz

Then the bandwidth is expressed as 12:1 banswidth

WAVE PROPAGATION AND ANTENNAS Fundamental Parameters
 ANTENNA POLARIZATION

“property of an electromagnetic wave describing the

time-varying direction and relative magnitude of the
electric-field vector”
ANTENNA POLARIZATION
CIRCULAR POLARIZATION

For a circular polarized wave:

a. The field must have two orthogonal linear components, and

b. The two components must have the same magnitude, and
c. The two components must have a time-phase difference of odd multiples of 90◦
POLARIZATION LOSS FACTOR (PLF)
Let the incident field be, and the polarization of the E field for the receiving
antenna be,

Where , and are the unit vectors ( or the polarization vector) of the incoming wave
and the receiving antenna
SENSE OF POLARIZATION CIRCULAR

https://antennatestlab.com/wp-content/uploads/2017/09/CP-Explained-Without-Math.pdf

• GPS è RHCP
• Mobile/wireless application è circular polarization

• From Circular to linear polarization, 3dB loss

SENSE OF POLARIZATION CIRCULAR

https://medium.com/illumination/how-do-3d-glasses-work-12304df48757
 SIMULATION EXERCISE 2
Design an inset fed patch antenna operating at 2.4 GHz.
1) Compare the radiation pattern of the patch antenna with the dipole antenna designed in tutorial 1
2) Compare the gain and directivity of the patch antenna with the dipole antenna designed in tutorial 1
3) What is the bandwidth of the antenna?
4) Plot the axial ratio, what is the polarization of the antenna
WAVE PROPAGATION AND ANTENNAS Fundamental Parameters
 ANTENNA INPUT IMPEDANCE (TX)

Maximum power delivery è

 RADIATION EFFICIENCY

Remember!!!

Antenna efficiency è

Radiation efficiencyè
ANTENNA INPUT IMPEDANCE (TR)
ANTENNA APERTURE

S(Watts/m2) = P(watts) / A(m2)

Incident Wave
ZL with Poynting
A(m2) = the aperture area
Vector S
(watts/m2)

A = It is an aperture over which the antenna extracts

power from an incoming wave

The effective aperture is related to the directivity by:

Receiving
antenna

4πA
D= !
!
FRIIS EQUATION

! %
!! = (!$)x( ) x(Gt)x(Gr)xPLF
"#$

assuming 1) no reflection
2) polarization matched
3) aligned transmitter with receiver at maximum directivity
!
!! = (!$)x("#$)%x(Gt)x(Gr)
ANTENNAS Impedance matching
 QUARTER WAVE TRANSFORMER
• Very simple but it can match real loads ONLY!
EXAMPLE
 IMPEDANCE MATCHING
• Impedance matching is used to Maximize power delivery to the load
• It is most of the time possible to match at a single frequency. However, a wideband matching network is
possible but challenging sometimes!
 LUMPED ELEMENTS MATCHING (L-NETWORK)
• Impedance matching is used to Maximize power delivery to the load
• It is most of the time possible to match at a single frequency. However, a wideband matching network is
possible but challenging sometimes!

Inside 1+JX circle Outside 1+JX circle

 IMPEDANCE MATCHING ( SINGLE STUB )
• Can be fabricated as part of the circuit. No need to solder components.

Shunt stub Series stub

 SHUNT SINGLE STUB
• Normalize the load impedance and plot it in smith chart.
• Locate the corresponding admittance
• Move from the YL point towards the generator until you intersect the 1+jb circle.
• The corresponding travel distance is the distance between the load and the stub (d).
• The length of the stub is the distance starting from the short circuit ( or the open circuit) until you reach the
-jb point.
• Another solution exists by taking the length d which intersects the constant 1+jb circle from the lower part
of the smith chart. Then, take the other stub from the short circuit ( or the open circuit) until the +jb point.
EXAMPLE
SOLUTION 1
SOLUTION 1
WAVE PROPAGATION AND ANTENNAS Feeding Network
FEEDING OF MICROSTRIP LINE
Inset feed edge feed

Antenna-Theory.com Antenna-Theory.com
FEEDING OF MICROSTRIP LINE
Coax feed coupled feed

Antenna-Theory.com Antenna-Theory.com
FEEDING NETWORK
 FEEDING NETWORK
200 Ω 200 Ω

Design a 5.8 GHz 2 to 1 feeding network.

50 Ω