Goals
In
this experiment, monopole antenna will be designed by using CST Studio.
Fundamental characteristics of the monopole antenna will be understood and
studied. Results of monopole antenna are examined how to change as regard width
(w) and length (l). Also, a Planar Inverted-F antenna (PIFA) will be searched
and studied and designed for a mobile phone.
Introduction
A monopole antenna is part of a
dipole antenna and is nearly invariably positioned over a ground plane. Figure
1 illustrates the case of an L-length monopole antenna mounted over an infinite
ground plane.
Figure 1.Monopole above a
PEC (a), and the equivalent source in free space (b). [1]
The
fields above the ground plane can be detected using image theory by using an analogous
source (antenna) in free space, as seen in Figure 1. (b). This is actually a
double-length dipole antenna. Figure
1(a) shows the fields above the ground plane, which are the same as the fields
in Figure 1(b). In Figure 1(a), the monopole antenna fields below the ground
plane are zero. The dipole result also shows the radiation pattern of monopole
antennas above a ground plane. The only difference to be aware of is that a
monopole antenna's impedance is half that of a true dipole antenna. Since the
impedance of a quarter-wave monopole (L=0.25*λ) is half that of a half-wave
dipole, Zin = 36.5 + j21.25 Ω. This is understandable since a
monopole antenna needs half the voltage to move the same current as a dipole
antenna. The monopole antenna's impedance is halved since Zin = V/I.
A
monopole antenna's directivity is proportional to that of a dipole antenna. If
the directivity of a dipole of length 2L is D1, the directivity of a monopole
antenna of length L would be D1+3 [decibels]. That is, a monopole antenna's
directivity (in linear units) is twice that of a dipole antenna of the same
length. The explanation for this is that no radiation exists below the ground
plane, resulting in the antenna being half as "directive".
Monopole
antennas are half the size of dipole antennas, making them appealing when a
small antenna is needed. Older mobile phone antennas were typically monopole
antennas with an infinite ground plane approximated by the phone's shell
(casing).
1.1.
The Monopole Antenna and the Consequences of a Finite
Scale Ground Plane
Monopole
antennas are used on finite-sized field planes in practice. This has an
influence on the monopole antennas' properties, especially the radiation
pattern. For ground planes of at least a few wavelengths in size around the
monopole, the impedance of a monopole antenna is minimally influenced by a
finite-sized ground plane. A finite sized ground plane, on the other hand, has
a significant impact on the monopole antenna's radiation pattern. The resulting
radiation pattern radiates out from the horizontal plane in a
"skewed" direction. The following Figure 2 provides an example of the
radiation pattern for a quarter-wavelength monopole antenna (oriented in the +z
-direction) on a ground plane with a diameter of 3 wavelengths.
Figure 2.Radiation Pattern
of Monopole Antenna [1]
It's
worth noting that the monopole antenna's resultant radiation pattern is still
omnidirectional. However, the peak-radiation path has moved from the x-y axis
to an angle above the plane. In general, the greater the ground plane, the
lower the overall radiation direction; as the ground plane reaches infinite
scale, the x-y plane radiation pattern approaches a maximum.
1.1.
History of the Monopole Antenna
Radio
pioneer Guglielmo Marconi designed and patented the monopole antenna in 1895
during his historic first work in radio communication. He started by using
Heinrich Hertz's dipole antennas, which consisted of two parallel horizontal
wires terminating in metal plates. Through experimenting, he discovered that
instead of using a dipole, he could transmit for longer distances by connecting
one side of the transmitter and receiver to a wire hanging overhead and the
other side to the Earth. The monopole is also known as a Marconi antenna,
despite the fact that Alexander Popov independently developed it at the same
time.
Figure 3.Marconi’s Patent
First Monopole Antenna [2]
Drawing
from Marconi's 1896 patent depicting his first monopole antennas, which consisted
of suspended metal plates (u, w) fixed to the transmitter (left) and receiver
(right), with one hand grounded (E). He later discovered that the plates were
pointless and that a suspended wire sufficed.
Figure
4 demonstrates the first monopole transmitter of Marconi’s antenna.
Figure 4.Marconi’s First
Monopole Transmitter [2]
A
small metal plate hanging from a wooden arm with a long wire going down to the
transmitter in the building was one of Marconi's early monopole antennas at his
Poldhu, Cornwall transmitting station in 1900.
Figure 5.Marconi’s Cornwall
transmitting station
1.1.
Radiation pattern
The
omnidirectional radiation pattern of a monopole antenna is similar to that of a
dipole antenna: it radiates with equal power in all azimuthal directions
perpendicular to the antenna. The radiated power, on the other hand, varies
with elevation angle, with zero radiation at the zenith of the antenna axis. It
emits radio waves that are vertically polarized. A monopole can be visualized
(right) as a vertical dipole receiving wire (c) with the foot half supplanted
by a conducting plane (ground plane) at right points to the remaining half. The
radio waves from the remaining upper half of the dipole (a) transmitted from
the ground plane would tend to originate from a picture antenna (b) forming the
missing half of the dipole, leading to the direct radiation to create a dipole
radiation pattern if the ground plane is wide enough. So the design of a
monopole with a flawlessly conducting, interminable ground plane is
indistinguishable to the beat half of a dipole design, with its greatest
radiation within the level course, opposite to the radio wire. Since it
transmits as it were into the space over the ground plane, or half the space of
a dipole radio wire, a monopole radio wire will have a pick-up of twice (3 dB
more prominent than) the pick-up of a comparative dipole receiving wire, and a
radiation resistance half that of a dipole. Since a half-wave dipole has a gain
of 2.19 dB and a radiation resistance of 73 Ω, a quarter-wave monopole, which
is the most common kind, would have a gain of 2.19 + 3 = 5.19 dB and a
radiation resistance of around 36.8 Ω if installed over a good ground plane.
Figure 6.Radiation Pattern
of Monopole Antenna over Perfect Ground [2]
Figure
6 represents appearing the monopole radio wire has the same radiation design
over culminate ground as a dipole in free space with twice the voltage.
Electrically
small field planes, as well as imperfectly conducting earth grounds, have the
effect of tilting the highest radiation path up to higher height angles.
1.1.
Types of Monopole Antenna
The Earth is typically the ground plane for monopole antennas working at lower frequencies, below 20 MHz; in this situation, the antenna is mounted on the ground and one side of the feedline is attached to an earth ground at the antenna's base. A circular network of buried wires extending outward from the antenna is commonly used in transmitting antennas to minimize ground resistance. The mast radiator transmitting antennas used for radio broadcasting in the MF and LF bands are based on this configuration. At lower frequencies, the antenna mast is electrically small, resulting in a very low radiation resistance, so capacitively top loaded monopoles like the T-antenna and umbrella antenna are used to improve efficiency.
Figure 7.Radiation pattern
of 3/2 wavelength monopole [2]
Figure
7 shows radiation design of 3/2 wavelength monopole. Monopole radio wires up to
1/2 wavelength long have a single "projection", with field quality
declining monotonically from a greatest within the flat heading, but longer
monopoles have more complicated designs with a few funnel shaped
"flaps" (radiation maxima) coordinated at points into the sky.
Since
the ground plane needed at VHF and UHF frequencies is smaller, artificial
ground planes are used to allow the antenna to be placed above the ground. A
common sort of monopole radio wire at these frequencies comprises of a
quarter-wave whip radio wire with a ground plane comprising of a few wires or poles
emanating on a level plane or askew from its base; this is often called a
ground-plane receiving wire. At gigahertz frequencies the metal surface of a
car roof or plane body makes a great ground plane, so car cell phone radio
wires comprise of brief whips mounted on the roof, and airplane communication receiving
wires as often as possible comprise of a brief conductor in an aerodynamic
fairing anticipating from the fuselage; usually called an edge radio wire.
Monopole
antennas include quarter-wave whip and rubber ducky antennas used in mobile
radios like walkie-talkies and compact FM radios. The inverted - F antenna,
which is a version of the inverted - L monopole, is used in mobile phones.
Bowing over the receiving wire spares space and keeps the it inside the bounds
of the mobile's case but the radio wire at that point features an exceptionally
low impedance. To make strides the coordinate the radio wire is not nourished
from the conclusion, or maybe a few halfway point, and the conclusion is
grounded instep.
The
antenna in these portable devices lacks an adequate ground plane, and the
transmitter's ground side is simply attached to the ground link on its circuit
board. The antenna/ground combination which act more like an asymmetrical
dipole antenna than a monopole since the circuit board ground is always smaller
than the antenna. The person carrying them would be able to
use his or her hand and body as a makeshift ground plane.
Some
of the time, monopole radio wires are printed on a dielectric substrate to form
it less delicate and they may be manufactured effortlessly utilizing the
printed circuit board advances. Such radio wires are known as printed monopole receiving
wires. They are appropriate for different applications such as RFID and remote
organizing.
Figure 8.VHF ground plane
antenna [2]
Above
figure is VHF ground plane radio wire, a sort of monopole radio wire utilized
at high frequencies. The three conductors anticipating descending are the
ground plane.
1.1.
PIFA - The Planar Inverted - F Antenna
An
inverted - F antenna is a type of wireless communication antenna. It consists
of a monopole antenna that is grounded at one end and runs parallel to a ground
plane. The antenna is fed from a distance away from the grounded end, at an
intermediate stage. The antenna is shorter and more compact than a simple
monopole, and the impedance matching can be operated by the manufacturer
without the need for additional matching parts.
Figure 9. An Inverted-F
Antenna in a DECT [3]
Patch antennas are a type of patch
antenna. There are several variations of this, as well as other types of
inverted - F antennas, that implement wideband or multi-band antennae. Coupled
resonators and the insertion of slots are examples of techniques. The
inverted - F antenna was first conceived as a bent-wire antenna in the 1950s.
However, because of its space-saving properties, it is most often used as a
planar inverted - F antenna (PIFA) in handheld wireless applications. PIFAs can
be printed within the microstrip format, which may be a commonly utilized
innovation that empowers printed RF components to be delivered nearby other
components on the same printed circuit board.
Figure
10.
The Planar Inverted-F Antenna (PIFA) [4].
Because of the shorting pin at the top,
the PIFA is resonant at a quarter-wavelength. The feed is positioned between
the open and shorted ends, controlling the input impedance. A plate can be used
as a shorting pin in PIFAs, as seen in Figure 11:
Figure 11. The Planar
Inverted-F Antenna (PIFA), with a shorting Plane [4].
We
have a PIFA with a length of L1 and a width of L2. The W-width shorting pin (or
shorting post) starts at one side of the PIFA, as seen in Figure 11. The feed
point is on the same edge as the illustration. D is the difference between the
feed and the shorting pin. From the ground plane, the PIFA is at a height of h.
As with the patch antenna, the PIFA rests on top of a dielectric with
permittivity ɛr. The feed distance to the short pin may be used to
monitor the PIFA's impedance (D). The impedance decreases as the feed gets
closer to the shorting pin; the impedance increases as the feed gets farther
away from the short tip. This parameter can be used to adjust the impedance of
the PIFA. The PIFA's resonant frequency is determined by W. If W=L2, the
shorting pin will run the length of the patch [4].
Assume W=0, which means the short is just
a pin (or assume W L2). The PIFA is then resonant at:
In common, we will inexact the thunderous
length of a PIFA as a work of its parameters as:
To
make things concrete, in our example, L1 = 20 mm, L2 = 10 mm, W = 2 mm, D = 0.2
mm and epsilon is 3.8.
L1
+ L2 – W = 28 mm = 0.028 m= 
As a result, the resonance frequency is 1.374 GHz which is calculated result.
Method
Question
1
A
ground made of copper is made for the construction of monopole antenna. The
width of the ground is 238 mm, and the length of the ground is 238 mm. The
thickness of the ground is 0.03 mm. Figure 12 shows ground plane.
Figure 12. Ground plane
A
wire was placed in the middle of the ground. The high of the wire is 70 mm and
the thickness of the wire is 2 mm. A gap of about “g” (1 mm) is left between
the wire and the ground to feed the wire. This is shown Figure 13.
Figure
13.
Wire which placed ground.
Question
2
All of the steps in question 1 were done again in question 2. One coaxial cable was added and the coaxial cable was positioned from -10 to 0 on the y-axis. This is shown in Figure 14.
Figure
14.
Coaxial Cable was placed.
Dielectric material was added to the inner coaxial cable, and then the outside of the cable was covered with PEC. This is shown in Figure 15.
Figure
15.
Outside of Coaxial Cable
Question
3 (Homework)
Last question of this experiment, PIFA
antenna was designed for mobile phones. Firstly, a ground was designed and its
dimension is 30 mm, 30 mm and 0.03 mm, respectively. It made of PEC. Then, a block
was designed above ground. Its dimensions are 20 mm, 10 mm and 4 mm,
respectively. It made of a special material which εr is 3.8. Top of
brick was covered a PEC material. In addition, a feed point was designed and it
was feed a discrete port. Also, a short port was designed to complete circuit.
All things what are done is shown in Figure 16.
Figure
16.
Designed PIFA Antenna
Results
Result
1
In first question of experiment, monopole antenna was
designed as Figure 13 and it was simulated. S- Parameter of monopole antenna is
shown in Figure 17. Resonance Frequency is 0.99772 GHz and resonance value
of it is -17.108 dB, according to Figure 18.
Figure
17.
S- Parameter of monopole antenna
Figure
18.
Resonance frequency and value monopole antenna
According to Figure 19, monopole antenna
works -10 dB at 0.92467 GHz and 1.0929 GHz. Therefore, bandwidth of this
antenna is 0.16823 GHz (1.0929 – 0.92467) at -10 dB. At -10 dB, efficiency of monopole
antenna is 90%.
Figure
19.
Values of S-Parameter at -10 dB
According to Figure 20, monopole antenna
works -3 dB at 0.80391 GHz and 1.5279 GHz. Bandwidth of this antenna is 0.724
GHz (1.5279 – 0.80391) at -3 dB. At -3 dB, efficiency of antenna is 50%.
Figure
20.Values
of S-Parameter at -3 dB
In Figure 21 is seen S - Parameters of monopole antenna with changing W (width) from 222 mm to 238 mm. Figure 22 is more detailed version of Figure 18.
Figure
21.
S - Parameters of monopole antenna with changing W (width)
According
to Figure 22, as the width of the ground increases, the operating intensity of
the monopole antenna increases. To comment the figure, more width caters more
efficient to the system. Therefore, as in the figure, when width equals to 238,
it has the best efficiency.
Figure
22.
More detailed version of Figure 17
In Figure 23, total efficiency of monopole antenna with changing W (width) is
shown. According to Figure 23, total efficiency is maximum at resonance
frequency (0.99 GHz). Its value is approximately % 98.
Figure
23.
Efficiency of Monopole Antenna with changing W (width)
Figure 24 is more detailed version of Figure 23. It can be seen that, the wider of ground, the more efficiency of monopole antenna in Figure 24.
Figure
24.
More detailed version of Figure 19
Since the lower plane is not infinite, the farfield of monopole antenna looks like an apple in Figure 25. If the plane were infinite, the farfield would look like half an apple.
Figure 25. Farfield of Monopole Antenna at 1 GHz.
The H and E plane of monopole antenna cuts are shown
in Figure 26.
Figure 26. The H and E plane of monopole antenna
In Figure 27 is seen S - Parameters of monopole
antenna with changing L (length) from 222 mm to 238 mm. Figure 28 is more
detailed version of Figure 27.
Figure 27. S - Parameters of monopole antenna with changing L (length)
According to Figure 28, as the length of the ground increases, the operating intensity of the monopole antenna increases.
Figure 28. More detailed
version of Figure 24
In Figure 29, total efficiency of monopole antenna with changing L (length)
is shown. According to Figure 29, total efficiency is maximum at resonance
frequency (0.99 GHz). Its value is approximately % 98.
Figure 29. Efficiency of Monopole Antenna with changing L (length)
Figure 30 is more detailed version of Figure 29. It can be seen that, the longer of ground, the more efficiency of monopole antenna in Figure 30.
Figure 30. More detailed version of Figure 26
The H and E plane of monopole antenna cuts are shown
in Figure 28.
Figure 31. The H and E plane of monopole antenna
Result
2
In second question of experiment, monopole antenna with coaxial port was designed as Figure 15 and it was simulated. S- Parameter of monopole antenna with coaxial port is shown in Figure 32. Resonance frequency is 1.0041 GHz and resonance value of it is -16.8424 dB, according to Figure 33.
Figure 32. S- Parameter of monopole antenna with coaxial port
Figure
33.Resonance
frequency and value monopole antenna with coaxial port
According to Figure 34, monopole antenna
with coaxial port works -10 dB at 0.93071 GHz and 1.1405 GHz. Therefore,
bandwidth of this antenna is 0.20979 GHz (1.1405 – 0.93071) at -10 dB. At -10
dB, efficiency of monopole antenna is 90%.
Figure
34.
Values of S-Parameter at -10 dB
According to Figure 35, monopole antenna
with coaxial port works -3 dB at 0.82641 GHz and 1.6462 GHz. Bandwidth of this
antenna is 0.81979 GHz (1. 6462 – 0. 82641) at -3 dB. At -3 dB, efficiency of
antenna is 50%.
Figure
35.
Values of S-Parameter at -3 dB
In Figure 36, total efficiency of monopole antenna with coaxial port is
shown. According to Figure 36, total efficiency is maximum at resonance
frequency (1 GHz). Its value is approximately % 98.
Figure
36.
Efficiency of Monopole Antenna with coaxial port
Figure 37 shows farfield 3D plotting
of monopole antenna with coaxial port at 1 GHz (resonance frequency).
Figure 37. Farfield of
Monopole Antenna with coaxial port at 1 GHz.
The H and E plane of monopole antenna cuts are shown
in Figure 38.
Figure
38.
The H and E plane of monopole antenna with coaxial port
Result
3 (Homework)
When
the w (width) is changed from 0.5 to 4 with the step size 0.5, CST Studio gives
us below result. What we understood from Figure 39 is that when the width which
equals to 3, gives better efficiency for PIFA (The Planar Inverted - F)
antenna.
Figure 39. The S Parameters
of PIFA Antenna by Changing Width
The
maximum efficiency for the PIFA antenna is when the w = 3 mm. The return loss
value for that is represented Figure 40.
Figure 40. The S Parameter
of the PIFA Antenna when w = 3 mm
From the Figure 41, the resonance frequency of the PIFA antenna is 1.77 GHz and its efficiency is -26.619 dB.
Figure 41. Detail Information of the S parameter of PIFA Antenna
Figure 42 shows the farfield representation of the PIFA antenna at 2.5 GHz and θ = 90°. According to the Figure 42, the main lobe magnitude is 0.883 dB and its direction is 95°. Angular width at the half efficiency is 113.1°. The side lobe level is 2.3 dB.
Figure 42. The PIFA Antenna
Farfield Representation when w = 3 mm and θ = 90
Figure
43 shows the farfield representation of the PIFA antenna at 2.5 GHz and Φ = 90°.
According to the Figure 43, the main lobe magnitude is 0.874 dB and its
direction is 86°. Angular width at the half efficiency is 134.1°. The side lobe
level is 2.7 dB.
Figure 43. The PIFA Antenna
Farfield Representation when w = 3 mm and Φ = 90
Figures
44 and 45 show the results when we change the distance (d). According to figures,
we perceive that when the distance (d) approach to 0, it gives more effective
results. Therefore, it is perceived that the low distance is better choice when
we design PIFA antennas.
Figure 44. S Parameters of
the PIFA when w = 3 mm by Changing d
Figure 45. S Parameters of
the PIFA when w = 3 mm by Changing d with 0.1
Step Size
Figure
46 represents the result when d = 0.1 and width w = 3. It gives that resonance
frequency is 1.685 GHz and its efficiency value is 15.815 dB.
Figure 46. S Parameters of
the PIFA when w = 3 mm and d = 0.1 mm
The
total efficiency and radiation efficiency of the PIFA antenna is represented Figure
47. Green color represents Total efficiency and red color represents radiation
efficiency. Total efficiency is derived by radiation coefficient and radiation
efficiency of antenna. Figure 47 shows that, at 1.77 GHz, the efficiency is
below the half efficiency level.
Figure 47. Radiation and
Total Efficiency of the PIFA Antenna
The
farfield representations of PIFA antenna is shown in Figure 48. According to Figure
48(a), when θ = 90°, main lobe magnitude is 0.235 dB. Main lobe means that the
lobe containing the higher power. As we can understand the Figure 48(a), main
lobe direction is 131° and represented by blue color in Figure 48(a). When Φ = 90°,
main lobe magnitude is 0.314 dB and it means radiated signal strength reaches
maximum point here. According to the Figure 48 (b), its degree is 157° and blue
color line shows its direction.
Figure 48. The Farfield Represantations
of the PIFA Antenna
Conclusion
Monopole
antenna and PIFA antenna were investigated. Using the CST program, monopole
antenna and monopole antenna with coaxial port were designed and how the
results change according to w (width) and l (length) were examined. The working
principle of the PIFA antenna was investigated and various simulations of the
designed PIFA antenna were made to determine the optimum range for the PIFA
antenna to operate. The results of PIFA were compared according to both l
(length) and w (width). The use of the PIFA antenna in daily life was learned.
1- Antenna Theory, The Monopole Antenna, 2021, reached by site https://www.antenna-theory.com/antennas/monopole.php
2- Wikipedia, Monopole antenna, 2021, reached by site https://en.wikipedia.org/wiki/Monopole_antenna
3- Wikipedia, Inverted-F antenna, 2021, reached by site https://en.wikipedia.org/wiki/Inverted-F_antenna
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