Goals
In this experiment, it was aimed to research circular and square loop antennas, to have information about these antennas, to design and simulate these antennas using the CST Studio program within the obtained information. Then, it is aimed to compare the theoretical knowledge learned with the simulation results.
Introduction
1.
General Information
A
loop antenna is a type of radio antenna that consists of a wire loop or coil,
tubing that receives primarily the magnetic portion of an electromagnetic wave,
or another electrical conductor that is normally fed by a balanced source or
feeding a balanced load. There are two types of antennas described in this
physical description:
Figure 1. A Shortwave Loop Antenna [1]
As compared to the working wavelength, small loop antennas have a small perimeter. They can be used for both transmission and reception, but antennas that are small in comparison to the wavelength are inefficient radiators and are thus only used for reception. The ferrite (loopstick) antenna used in most AM broadcast radios is an example. A small loop antenna's radiation pattern has two sharp nulls in opposite directions. Small loops are used for radio direction finding (RDF) to identify radio signal sources because of their portability and directional pattern.
1.1.
Frequency
Range
The loop antenna's operating frequency spectrum is about 300 MHz to 3 GHz. This antenna operates in the UHF frequency spectrum.
1.2.
Large Loop Antennas
Resonant
antennas are large loop antennas that are tuned to a certain frequency. They
have a high quality in terms of radiation. These antennas are about the same
length as the expected wavelength.
Where,
· λ is the wavelength of light· L is the antenna's length.
The perimeter length of this antenna, which should be around a wavelength and sealed, is the most important parameter. Meandering the loop to minimize its size is not a smart idea because it improves capacitive effects and reduces performance.
1.3.
Small Loop Antennas
Magnetic
loop antennas are another name for small loop antennas. These have a lower
resonance. Usually, they are used as receivers. These antennas are one-tenth of
a wavelength in height.
L = λ / 10
Where,
· λ is the wavelength of light· L is the antenna's length.
Small
loop antennas have the following characteristics:
· The radiation resistance of a small loop antenna is minimal. High radiation resistance can be obtained by using multi-turn ferrite core constructions.
· It has a compact design and is small in size and weight.· Owing to high losses, it has a poor radiation quality.
Its
impedance is difficult to align with the transmitter due to its high reactance.
This impedance mismatch would be a major issue if the loop antenna were to
serve as a transmission antenna. As a result, these loop antennas function well
as receiver antennas [2].
1.4.
Shape of Loop Antenna
Loop
antennas may be shaped like a circle, rectangle, or some other closed geometric
form with a diameter marginally greater than one wavelength. The quad antenna,
also known as a "quad," is a self-resonant loop in a square shape
that can be made out of wire strung over an X-shaped frame. As parasitic
elements, one or two additional loops can be stacked parallel to the first,
rendering the antenna system unidirectional with improved gain. This pattern
can also be rotated 45 degrees and supported on a ‘+' shaped frame to create a
diamond shape. Since they only need one elevated reinforcement, triangular
loops have also been used for vertical loops. [1] When used as a single unit, a
rectangle twice the height of its width has marginally increased gain and
matches 50 ohms directly.
Unlike a dipole antenna, a loop antenna's polarization is determined by the feed point (where the transmission line is connected) and whether it is run as a 1, 2, or 3 wavelength loop. When a vertically oriented loop is fed at its 1 wavelength frequency from the bottom, it becomes horizontally polarized; when fed from the edge, it becomes vertically polarized.
1.5.
Frequently Used Loops
There
are two kinds of small loop antennas.
· Antennas of a circular cord
· Antennas for square loops
These
two loop antenna types are the most common. Other shapes (rectangular, delta,
elliptical, and so on) are rendered to the designer's specifications as well.
Figure 1 represents circular loop antennas and Figure 2 shows the square loop antenna example.
Figure 2. Square Loop Antenna [2]
Circular
(Figure 1) and square (Figure 2) loop antennas are seen in the examples above.
Because of their high signal-to-noise ratio, these antennas are usually used as
AM receivers. They're also conveniently tunable in radio receivers' Q-tank
circuit [2].
1.6.
Polarization of Loop
Depending on the feed position, the polarization of the loop antenna would be vertical or horizontal. Based on the form of the ring antenna, the vertical polarization is given at the center of the vertical side and the horizontal polarization is given at the center of the horizontal side. In most cases, a short loop antenna is linearly polarized. When a small loop antenna is placed on top of a portable receiver, the output of which is attached to a meter, it becomes a powerful direction finder [2].
1.7.
Radiation Pattern
The figure above depicts the radiation pattern for thin, high-efficiency loop antennas. The radiation patterns for various looping angles are also clearly depicted in the diagram. Vertical polarization is indicated by the tangent line at 0°, while horizontal polarization is indicated by the line at 90°.
Figure 3. A Quad Antenna [1]
1.8.
Advantages
The
benefits of using a loop antenna are as follows:
· The scale is small.
· Directivity is high.
1.9.
Disadvantages
The
below are some of the loop antenna's drawbacks:
· It's possible that impedance matching isn't really a smart idea.
· Has a high efficiency factor for resonance.
1.10.
Applications
The
applications of the Loop antenna are as follows:
· RFID (radio frequency identification) devices
· MF, HF, and short wave receivers use it.
· For path finding in aircraft receivers.
· UHF transmitters use it. [2]
Method
Question 1
In Figure 4, a typical circular loop antenna has been designed using the Torus modeling method in the CST program. The radius of this circular loop antenna is 29.5 mm and this antenna is made of copper material. In addition, a discrete port has been defined to feed this circular loop antenna.
Figure 4. Designed Typical Circular Loop Antenna Using Torus Modeling Method
Figure 5.Designed Typical Circular Loop
Antenna Using Cylinder Modeling Method
Question 2
A typical square loop antenna is designed
in Figure 6. The width and length of the square loop antenna is 42 mm, and the
thickness is 1 mm. In addition, a 1 mm gap was created to feed the antenna and
a discrete port was defined from this gap. Square loop Antenna is made of
copper material.
Figure 6.Designed Typical Square Loop
Antenna
Question 3 (Homework 1)
In addition to the design
in question 1, 2 more typical circular loop antennas connected to s and m
parameters have been added in Figure 7. The purpose of this design is to
increase the performance of the circular loop antenna and achieve better
results.
Figure 7. Performance enhancement of
Circular Loop Antenna
Question 4 (Homework 2)
In addition to question 2, a planar plane is placed inside the square loop antenna. This design is shown in Figure 8. This was done by changing the dimensions of the added plane in order to obtain a better performance and result compared to the results found in the second question.
Figure 8. Performance enhancement of
Square Loop Antenna
Results
Result
1
Figure 9 is simulated and then Figure 10 shows s-parameter of designed typical circular loop antenna using Torus modeling method. Resonance Frequency is 1.746 GHz and resonance value of it is -6.807 dB, according to Figure 10.
Figure 9. S- parameter of Designed
Typical Circular Loop Antenna Using Torus Modeling Method
Figure 10. Resonance Frequency and Value Typical
Circular Loop Antenna Using Torus Modeling Method
According to Figure 11, circular loop
antenna works between 1.568 GHz and 1.985 GHz at -3 dB. Bandwidth of this
antenna is 0.417 GHz (1.985 – 1.568) at -3 dB. Under this conditions, there is not
s-parameter circular loop antenna at -10 dB because its resonance value - 6.807
dB, it cannot pass over -10 dB.
Figure 11. Values of S-Parameter of
Circular Loop Antenna Using Torus Modeling Method
at -3 dB
Figure 12. Efficiency of Circular Loop
Antenna Using Torus Modeling Method
Figure 13 shows farfield 3D plotting of circular loop antenna using Torus Modeling Method without directivity at 1.75 GHz (resonance frequency).
Figure 13.Farfield of Circular Loop
Antenna Using Torus Modeling Method without directivity at 1.75 GHz.
Figure 14 shows farfield 3D plotting of circular loop antenna using Torus Modeling Method with directivity at 1.75 GHz (resonance frequency).
Figure 14. Farfield of Circular Loop Antenna Using Torus Modeling Method with directivity at 1.75 GHz.
The H and E plane of circular loop antenna using Torus
Modeling Method cuts are shown in Figure 15.
Figure 15.The H and E plane of Circular Loop Antenna Using Torus Modeling Method
Figure 5 is simulated and then Figure 16
shows s-parameter of designed typical circular loop antenna using Cylinder
modeling method. Resonance Frequency is 1.785 GHz and resonance value of it is
-6.319 dB, according to Figure 17.
Figure 16. S- parameter of Designed
Typical Circular Loop Antenna Using Cylinder Modeling Method
Figure 17.Resonance Frequency and Value
Typical Circular Loop Antenna Using Cylinder Modeling Method
According to Figure 18, circular loop antenna works between 1.5942 GHz and 2.0333 GHz at -3 dB. Bandwidth of this antenna is 0.4391 GHz (2.0333 – 1.5942) at -3 dB. Under this conditions, there is not s-parameter circular loop antenna at -10 dB because its resonance value - 6.391 dB, it cannot pass over -10 dB.
Figure 18.Values of S-Parameter of
Circular Loop Antenna Using Cylinder Modeling Method at -3 dB
According to Figure 19, total efficiency
of circular loop antenna using Cylinder Modeling Method is maximum at resonance
frequency (1.78 GHz). Its value is approximately 75%.
Figure 19.Efficiency of Circular Loop
Antenna Using Cylinder Modeling Method
Figure 20 shows farfield 3D plotting of circular loop antenna using Cylinder Modeling Method without directivity at 1.78 GHz (resonance frequency).
Figure 20.Farfield of Circular Loop
Antenna Using Cylinder Modeling Method without directivity at 1.78 GHz.
Figure 21 shows farfield 3D plotting of circular loop antenna using Cylinder Modeling Method with directivity at 1.78 GHz (resonance frequency).
Figure 21. Farfield of Circular Loop
Antenna Using Cylinder Modeling Method with directivity at 1.78 GHz.
The H and E plane of circular loop antenna
using Cylinder Modeling Method cuts are shown in Figure 22.
Figure 22.The H and E plane of Circular Loop Antenna Using Cylinder Modeling Method
Result 2
After the simulation of the square loop
antenna designed in Figure 6, the s-parameter result of its design is shown in
Figure 23.
Figure 23. S- parameter of Typical Square Loop Antenna
Resonance Frequency is 2.07 GHz and resonance value of it is -6.913 dB, according to Figure 24.
Figure 24.Resonance Frequency and Value
Typical Square Loop Antenna
According to Figure 25, square loop antenna works between 1.8301 GHz and 2.2263 GHz at -3 dB. Therefore, bandwidth of this antenna is 0.3962 GHz (2.2263 – 1.8301) at -3 dB.
Figure 25. Values of S-Parameter of Square
Loop Antenna at -3 dB
In Figure 26, total efficiency of square
loop antenna is shown. According to Figure 26, total efficiency of square loop
antenna is maximum at resonance frequency (2 GHz). Its value is approximately 79.6%.
Figure 26.Efficiency of Square Loop
Antenna
Figure 27 shows farfield 3D plotting of square
loop antenna without directivity at 2 GHz (resonance frequency).
Figure 27. Farfield of Square Loop Antenna
without directivity at 2 GHz
Figure 28 shows farfield 3D plotting of square loop antenna with directivity at 2 GHz (resonance frequency).
Figure 28. Farfield of Square Loop Antenna
with directivity at 2 GHz
The H and E plane of circular loop antenna
using Cylinder Modeling Method cuts are shown in Figure 29.
Figure 29. The H and E plane of Square Loop Antenna
Result
3
While
designing in the Enhancement of Circular Loop Antenna part, our simulation is
applied until it reaches the appropriate value by changing the s and m
parameters. When s = 2.25 and m = 3 values are suitable for this antenna
design. The figure 30 expresses the s-parameter for these values.
Figure 30. Enhancement of Circular Loop Antenna s-parameter with s = 2.25 and m = 3
According to Figure 31, if the s-parameter in the design is interpret that for the first homework given in more detail is made, it can be seen that designed antenna has a bandwidth of 0.44 GHz, ie 440 MHz at -3 dB. This value is good value for a 440 MHz bandwidth antenna. It is especially good compared to antennas made on PCBs. The fact that designed antenna can be operated up to -59 dB is proof that the efficiency of the antenna is good.
Figure 31. Enhancement of Circular Loop Antenna s-parameter with s = 2.25 and m = 3 bandwidth at -3 dB
According to Figure 32, when bandwidth of the antenna is looked at -10 dB, it is found that the range is very low. Approximately 150 MHz is not a very good value. Being able to make this part wider would have been a good trend for the antenna's design. However, this was the last result we got with the parameters, and this result represents the best result we have.
Figure 32. Enhancement of Circular Loop Antenna s-parameter
with s = 2.25 and m = 3 bandwidth at -10 dB
Generally,
if the s parameter of the antenna is interpreted, the antenna can operate with
efficiency up to -58 dB. This is really a desired value. Of course, this value
is not as much in real life, but getting this value in simulation is proof that
it will be gotten a good result in real life. The operating resonance frequency
of the antenna was found to be approximately 1.57 GHz.
When the value of m is changed, the s parameter characteristic shown by the antenna is as in the Figure 33. Here the red, green and blue plots represent the values of m = 2,3 and 4 respectively. If the results are interpreted, it can be said that the value of m = 3 behaves more efficiently and therefore the dB value is lower. In other words, for the red wave, the efficiency is the least for the value of m = 2 and we can say that the resonance frequency shifts slightly. For the value of m = 4, the resonance frequency has shifted the most, but this value is not preferred because the efficiency is lower than m = 3.
Figure 33. Enhancement of Circular Loop
Antenna s-parameter with changing m value
To interpret efficiencies for the value of m = 2,3 and 4, the
statements which it is mentioned earlier, are valid here. The efficiency is
higher for m = 3, according to Figure 34.
Figure 34. Total Efficiency
of Enhancement of Circular Loop
Antenna s-parameter with changing m value
In Figure 35, the red, blue and green colors represent the values of s = 2, 3 and 4 respectively. As seen in the graph, since the dB value of the s = 3 value is lower, we can take this value as a reasonable value. For this value, it can be said that the bandwidth is approximately 400 MHz. However, it can be said that the value of dB before and after the value s = 3 is sharply rising and it can be observed that these values are not good values for the design of the antenna.
Figure 35. Enhancement of Circular Loop Antenna s-parameter with changing s value
According to Figure 36, to interpret the
effect shown for s = 2, 3 and 4 values, it can be said that the efficiency of
the antenna is high at s = 3. It is mentioned this observation in the previous
graph.
Figure 36. Total Efficiency of Enhancement
of Circular Loop Antenna s-parameter with changing s value
According to Figure 37, in order to make antenna is designed better and to obtain the optimum result, it is tested the system in s = 2 to 4 and m = 2 to 4 in simulation environment and obtained approximately 25 different results. When it is compared results, it is observed that m = 3 and s = 2.25 gives the ideal dB and s parameter result.
Figure 37. Enhancement of Circular Loop
Antenna s-parameter with changing s and m values
Designing and finding that results are yielded an efficient result for s = 2.25 and m = 3 values. The s parameter for these values is as in the Figure 38.
Figure 38. S-parameter of Enhancement of Circular Loop
Antenna with s = 2.25 and m = 3
According
to Figure 39, to interpret the s parameter, it is obtained for the design at
the specified values, designed antenna works at -3 dB between 1.47 GHz and 1.84
GHz values. In other words, designed antenna works with approximately 370 MHz
bandwidth. The resonance frequency it operates continues to operate at
approximately 1.51 GHz and at -40 dB.
Figure 39. Enhancement of Circular Loop
Antenna s-parameter with s = 2.25 and m = 3 bandwidth at -3 dB
In Figure 40, designed antenna works between 1.52 and 1.65 GHz for at -10 dB. In other words, it works at approximately 300 MHz bandwidth.
Figure 40. Enhancement of Circular Loop
Antenna s-parameter with s = 2.25 and m = 3 bandwidth at -10 dB
For this design, the operating resonance of designed
antenna is 1.593 GHz and it operates at approximately -40 dB at this frequency
as regard Figure 41.
Figure 41. Resonance Frequency and Value Enhancement
of Circular Loop Antenna
According
to Figure 42, if the efficiency graph of the design is interpreted, it works in
the 98% band of total and radiation efficiency in this design. This is an ideal
result for an antenna design.
Figure 42. Total Efficiency of Enhancement of Circular Loop Antenna
Figure 43 and 44 show the results of the farfield result of the antenna in dB and linear type. If the visuals are interpreted, the system's directivity at 1.59 GHz is -3.8 dB, that is, 2.4 in linearly. This is a really good value for loop antenna design. It can be thought that the system is oriented up and down due to the design made and it can be said that the farfield result came out as expected in our research.
Figure 43. Farfield of Enhancement of Circular Loop Antenna in dB Scalar
Figure 44. Farfield of Enhancement of Circular Loop Antenna in Linear Scalar
The
Figure 45 and 46 above are the farfield results of designed antenna at θ = 90°
and Φ = 90°. To interpret the results, it has a main lobe magnitude of 2.42.
For θ =90°, there is an orientation of 81.2° at 3 dB, and for Φ = 90°, we can
state that there is a dB orientation of 111.7°.
Figure 45. Radiation
Pattern of Enhancement of Circular Loop
Antenna
Result
4
In order to find a better result,
s-parameter graphs that change depending on the n parameter are shown in
Figures 46 and 47. In Figure 46, the value of n has the values of 4, 5, 6 and
7, respectively.
Figure 46. S-parameter of Performance enhancement of Square Loop antenna for n =3, 4, 5, 6 respectively
Figure 47. S-parameter of Performance
enhancement of Square Loop antenna for n =2, 3, 4 respectively
Figure 48 shows the total efficiency
values of n = 2, 3 and 4 values.
Figure 48. Total efficiency values of n =
2, 3 and 4 values
After some simulations, the best result was obtained when n = 3. When n = 3, s-parameter graph is given in Figure 49. In Figure 50, the graphic which in Figure 49 has resonance frequency and resonance value.
Figure 49. S- parameter of Performance enhancement of Square Loop Antenna when n=3
Figure 50. Resonance Frequency and Value of
Performance enhancement of Square Loop Antenna when n=3
According to Figure 51, Performance
enhancement of Square Loop Antenna when n=3 works between 1.7984 GHz and 2.1201
GHz at -3 dB. Bandwidth of this antenna is 0.3218 GHz (2.1201 – 1.7984) at -3
dB.
Figure 51. Values of S-Parameter of
Performance enhancement of Square Loop Antenna when n=3 at -3 dB
According to Figure 52, Performance enhancement of Square Loop Antenna when n=3 works between 1.8933 GHz and 2.0034 GHz at -10 dB. Bandwidth of this antenna is 0.1101 GHz (2.0034 – 1.8933) at -10 dB.
Figure 52. Values of S-Parameter of
Performance enhancement of Square Loop Antenna when n=3 at -10 dB
According to Figure 53, total efficiency of Performance enhancement of Square Loop Antenna when n=3 is maximum at resonance frequency (1.948 GHz). Its value is approximately 100%.
Figure 53. Total efficiency of Performance
enhancement of Square Loop Antenna when n=3
Figure
54 shows farfield 3D plotting of Performance
enhancement of Square Loop Antenna when n=3
without directivity at 1.948 GHz (resonance frequency).
Figure 54.Farfield of Performance
enhancement of Square Loop Antenna when n=3 without directivity at 1.948 GHz
Figure 55 shows farfield 3D plotting of
Performance enhancement of Square Loop Antenna when n=3 with directivity at
1.948 GHz (resonance frequency).
Figure 55.Farfield of Performance enhancement of Square Loop Antenna when n=3 with directivity at 1.948 GHz
The H and E plane of Performance enhancement of Square Loop Antenna when n=3 cuts are shown in Figure 56.
Figure 56. H and E plane of Performance enhancement of Square Loop Antenna when n=3
Conclusion
To sum up the experiment, in this
experiment we saw the loop antenna design. We tested 4 different antenna
designs on the CST Studio program and we observed the results by changing the
parameters of each antenna we created and designed our antennas at the optimum
value of the results. Before starting our studies, we have thoroughly
researched loop antennas and learned about the behavior of the antenna in the
literature. Then, we continued our work by following the steps stated in the
experiment sheet. Our experiment consists of 4 steps. In the first step of the
experiment, we examined the circular loop antenna and evaluated the results. In
Experiment 2, we designed a square loop antenna and observed the results. The
remaining parts of the experiment were given as homework and necessary actions
were taken. In Experiment 3, we examined a loop antenna with interlocking
loops. We examined the behavior of the antenna by changing the m and s values
of the designed antenna, namely the thickness of the circle and the distance
between the circles. In Experiment 4, the Enhancement of Square Loop antenna
was examined. In Experiment 2, we put a square plate inside the design we made
and set the distance between this plate and the outer plate as n. Then we
observed the results by changing the value of n. In this section, we have
stated our comments in our report. In this way, we completed our report and
finished our experiment. In this experiment, we gained knowledge about loop
antennas with the necessary equipment in square and loop antenna types.
References
[1]
Wikipedia, 2021, Loop Antenna, reached by the site https://en.wikipedia.org/wiki/Loop_antenna
[2]
Tutorialspoint, 2021, Antenna Theory-Loop, reached by the site https://www.tutorialspoint.com/antenna_theory/antenna_theory_loop.htm
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