EKT341 Antenna and Propagation
Universiti Malaysia Perlis, UniMAP
Experiment 1
Half Wavelength Dipole Antenna
1. OBJECTIVES



Understanding the basic functions of a half wavelength Dipole antenna.
Measuring radiation pattern of E plane and H plane of a half wavelength Dipole antenna.
Measuring voltage standing wave ratio, input impedance and reflection coefficient of a
half wavelength Dipole antenna.
2. THEORY
A half wavelength Dipole antenna is a resonant type antenna and its input impedance is about
70 + j0 Ω. Radiation resistance of the half wavelength Dipole antenna is about 70 Ω as the
resistance component of input impedance is radiation resistance. Input impedance can be
transformed into direct resistance by adjusting the length of the antenna. Following formula
explains current rush of a half wavelength Dipole antenna with λ/2 in length.
Figure 1.1 shows a general half wavelength Dipole antenna structure and its current
distribution. In Figure 1.1 (a), the total length is half wavelength and in Figure 1.1 (b),
current distribution shows maximum at the feeding point and 0 at both ends.
(a)
Figure 1.1
(b)
Half wavelength Dipole antenna structure and its current distribution
Figure 1.2 shows the definition of plane in radiation pattern measurement. E plane and H
plane here are conveniently named for the better understanding and their real radiation
pattern planes are defined in the coordinate system. Figure 1.2 (a) is the definition of the
coordinate system and the thick black line is a Dipole antenna. Figure 1.2 (b) shows a front
1
area radiation pattern measured at the x-z plane when ø = 00 and θ rotates from 00 to 3600.
Measurement results showed maximum at θ = 900 and minimum at θ = 00 and 1800. Figure
1.2 (c) shows a front area radiation pattern measured at the x-z plane when θ is fixed at 900
and ø rotates from 00 to 3600. Measurement results showed omni directional characteristics as
ø is consistent at every angle.
z
0
θ=0
θ = 0 ~ 360
0
Ø=0
0
θ = 90
y
θ = 180
x
(a) Dipole antenna and coordinate system
(b) E (x-z) plane measurement
180
270
0
Ø = 0 ~ 360
0
θ = 90
0
0
Ø=0
(c) H (x-y) plane measurement
Figure 1.2 Dipole antenna E(x-z) plane and H(x-y) plane
Dipole Antenna Characteristics
Half wavelength Dipole antennas used in this experiment are two types: 914.5125 Mhz and
2.45 GHz and their wavelengths are as follows:
Frequency used: 914.5125 MHz
Wavelength λ = c / f = 3 X 108 / 915 X 106 = 328.04 mm
Half wavelength = λ / 2 = 164.02 mm
Frequency used: 2.45 GHz
Wavelength λ = c / f = 3 X 108 / 2.45 X 109 = 122.45 mm
Half wavelength = λ / 2 = 61.22 mm
* From hereinafter, 914.5125 MHz will be contracted to 914 MHz
2

Sleeve Dipole antenna
Figure 1.3 Data measured through 914 MHz Sleeve Dipole antenna.

PCB pattern type Dipole antenna
Figure 1.4 (a) shows the coordinate system and a PCB pattern type half
wavelength Dipole antenna resonating at 2.45 GHz frequency. Figure 1.4 (b) is E
(xy) plane radiation pattern and Figure 1.4 (c) is H (xz) plane radiation pattern.
PCB in this experiment is FR4 with dielectric permittivity of 4.6 and was
designed using 1.6 mm thick dielectric substance.
z
0
Ø = 0 ~ 360
0
θ=0
0
y
x
Ø=0
(a) Half wavelength Dipole antenna coordinate system
(b) E (x-y) plane radiation pattern
θ=0
0
θ = 0 ~ 360
0
Ø=0
0
(c) H (x-z) plane radiation pattern
Figure 1.4 PCB pattern type λ/2 Dipole antenna
3
3. COMPONENT AND EQUIPMENT
Wave and Antenna Training System (WATS 2002)
 2.45 GHz Yagi antenna
 2.45 GHz half wavelength dipole antenna
 914 MHz half wavelength Sleeve Dipole antenna
4. PROCEDURE
a) E Plane Radiation Pattern Measurement
1. Connect the system as shown in Figure 1.5. 50 Ω terminator needs to be
connected to the open antenna bracket.
Figure 1.5 System connection diagram for a half wavelength Dipole antenna
Radiation Pattern measurement
2. Mount a 2.45 GHz Yagi antenna to the side of the bracket of the transmitting
antenna to produce horizontal polarization wave.
3. Mount a 2.45 half wavelength dipole antenna to the top bracket of the receiving
antenna to produce horizontal polarization wave.
4. Keep the transmitting antenna in parallel with the receiving antenna and the distance
of 120 cm between them.
5. Turn on the power of the computer.
6. Click on the WATS2002 icon from the desktop to start the program.
7. Select COM1 for a serial port and the main screen of WATS2002 will appear.
8. Turn on the power of the system.
Note: Reset button should be pressed to be able to select menu from the computer screen.
4
9. Press Rad.P icon to measure radiation pattern.
10. Select 2.45 GHz frequency after the WATS2002 Radiation Pattern screen
appears on the computer screen.
11. For a maximum wave reception, adjust angle and the heights for both
transmitting and receiving antennas. It should be taken into consideration that
the transmitting antenna and the receiving antenna be paralleled.
12. Click on the CAL icon. Then the receiving antenna rotates right and left to
find the position for the maximum wave reception. This position is considered
as a basic angle of 0 degree. However 0 degree basic angle may not be
achieved due to the interference from the surrounding wave environment.
13. Select a value for AGC Calibration in CAL screen and record the value.
Select a value slightly less than the maximum radiation pattern value of -10
[dBm] and press OK button.
14. Click on the AUTO button to measure the radiation pattern. Then the
receiving antenna rotates 360 degrees automatically to check the reception
level and displays on the screen. Please record all the value with referring
to the template given in ‘RESULTS AND OBSERVATIONS’ section.
* Reset button needs to be pressed to stop the operation during the measurement. The computer
will turn to the main screen.
15. Press Normalize button to check the standardized radiation pattern type.
16. Record the angle at which the maximum electric power was received. If there
is more than one angle, choose either one.
17. Record the right and left half power point angles -3 [dB] lower than the
maximum power.
18. Calculate half power beam width (difference in angle between the right and
left power point).
19. Return to the original measurement data by pressing Normalize button again.
20. Press Reset button to return the motor to its original status. Then a message
asking to save measured data will pop-up.
21. Select YES and assign file name such as [E-horz] and save in the desired
directory. On completion of data saving, the reception motor returns to its
original position.
22. If selecting NO, the reception motor will return to its original position without
data saving.
23. Press OK button when the motor returns to its original position.
24. Press Find button to confirm the receiving level at a desired angle. As shown
in Figure 1.6, enter a desired angle and press enter button. Then the receiving
power intensity at a desired angle will be displayed on the right side of the
screen.
Figure 1.6 Find screen
5
b) Opposite polarization (Vertical / Cross Polarization) wave receiving experiment
1. Rotate the transmitting antenna 90 degrees upward to get vertical polarization and
keep the receiving antenna at its original position as shown in Figure 1.7.
Figure 1.7 Polarization experiment between receiving and transmitting antennas
in vertical relationship
2. Rotate the receiving antenna horizontally 360 degrees and measure receiving wave
levels. [E-vert] data measured now may not show clearly in the radiation pattern
screen as its value is minimal compared to the transmitting antenna rotating at 90
degrees. Also its radiation pattern may be strained due to the influence from the
surrounding environment. Please record all the value with referring to the
template given in ‘RESULTS AND OBSERVATIONS’ section.
3. Record the maximum level value of [E-vert] data shown on the right side of the
screen. Press Normalize data button to view standardized radiation pattern.
4. Calculate following [k] which is a comparative ratio of wave level received through
antennas at the equal calibration condition.
k = E-horz (max) / E-vert (max)
c) H Plane Radiation Pattern Measurement
H Plane radiation pattern refers to the x-y plane radiation pattern in Figure 1.2.
1. As shown in Figure 1.8, replace both receiving and transmitting antennas with 914
MHz half wavelength Sleeve Dipole antennas and connect to the top brackets to form
vertical polarization. 50 Ω terminator needs to be connected to the open antenna
bracket
6
Figure 1.8
System configurations for H plane measurement
2. Press Rad.P icon to measure radiation pattern.
3. Select 914 MHz and click on the CAL icon to start calibration.
4. Select a value for ACG Calibration in CAL screen and record the value. Select a
value slightly less than the maximum radiation pattern value of -10[dBm] and press
OK button.
5. Select AUTO button and rotate the receiving antenna 360 degrees horizontally. This
is an H plane radiation pattern and it shows consistent value in all direction. Please
record all the value with referring to the template given in ‘RESULTS AND
OBSERVATIONS’ section.
6. Press Normalize button to observe the standardized wave form pattern and press
Normalize button again to return to its original status.
7. Press RESET button to save currently measured data as [H-vert] and exit.
7
d) Antenna Characteristics Measurement
1. Connect the system as shown on Figure 1.9
Network
Analyzer
PCB
antenna
Figure 1.9 System chart for antenna characteristics measurement
2. Start calibration by selecting desired frequency and connector in the network
analyzer.
3. Connect the 2.45 GHz Dipole antenna used in the experiment to the network analyzer
port.
4. Measure and analyze antenna’s reflection coefficient at the resonant frequency. Save
and include this graph in your report.
5. Measure the input impedance at the resonant frequency of the antenna in the
experiment using Smith Chart. Save and include this graph in your report.
6. Measure the Standing Wave Ratio (SWR) at the resonant frequency. Save and include
this graph in your report.
7. Repeat Steps 1until 6 by using 914 MHz Sleeve Dipole antenna.
8
RESULTS AND OBSERVATIONS (REPORT GUIDELINES)
a) E plane Radiation Pattern (Horizontal Polarization) :
Value for ACG Calibration = _____________ dB
Please take and note the data as the following:
Maximum receiving power = _____________ dB, Angle = _______ 0
Left half power point angle = _________ 0
Right half power point angle = _________ 0
Half power beam width = _________ 0
9
b) Opposite Polarization (Vertical / Cross Polarization) wave receiving experiment:
Value for ACG Calibration = _____________ dB
Please take and note the data as the following:
Maximum receiving power = _____________ dB
k = _____________
Compare the size of the comparative radiation pattern of currently measured
[E-vert] data to that of previously measured [E-horz] data. You can plot both
radiation patterns on the same graph to see the differences.
10
c) H Plane Radiation Pattern (Vertical Polarization) :
Value for ACG Calibration = _____________ dB
Please take and note the data as the following:
Maximum receiving power = _____________ dB, Angle = _______ 0
Left half power point angle = _________ 0
Right half power point angle = _________ 0
Half power beam width = _________ 0
d) Antenna characteristics measurement:

2.45 GHz Dipole antenna

914 MHz Sleeve Dipole antenna
Please note and capture the figure of measurement (from VNA) of all the following:
o Resonant Frequency
o Input Impedance
o SWR
11