Department of Science and Technology Institutionen för teknik och naturvetenskap
Linköping University Linköpings universitet
g n i p ö k r r o N 4 7 1 0 6 n e d e w S , g n i p ö k r r o N 4 7 1 0 6 -E S
LiU-ITN-TEK-G--16/068--SE
Antenna Study for IoT Devices
Rickard Hedlund
2016-06-13
Antenna Study for IoT Devices
Examensarbete utfört i Elektroteknik
vid Tekniska högskolan vid
Linköpings universitet
Rickard Hedlund
Handledare Magnus Karlsson
Examinator Adriana Serban
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Bachelor of Science Thesis
Examiner: Adriana Serban Supervisor: Magnus Karlsson 29 June 2016
i
ABSTRACT
Linköping University of Technology Hedlund, Rickard: Title
Bachelor of Science Thesis, 30 pages June 2016
Bachelor: RF Electronics
Examiner: Associate Professor Adriana Serban
Keywords: Antenna , Patch, Meandered Inverted-F, Inverted-F
This thesis investigates the possibility to design printed circuit board (PCB) anten-nas with a maximum area size of 30 x 30 mm2
at 2.4 GHz. The resulting antenna parameters are compared to those of a commercial, more costly chip antenna, i.e., Antenova A5645. The antenna parameters that were evaluated were the antenna efficiency, the return loss and the voltage standing wave ratio(VSWR).
Three types of antennas were firstly selected to be designed, i.e., the patch antenna, Inverted-F antenna and Meandered Inverted-F antenna. Using basic antenna theory, general RF knowledge and through simulations performed with the dedicated soft-ware tool ADS, five antenna designs were finally selected to be manufactured. After manufacturing, the antennas were tested in a radiation chamber. At 2.4 GHz, the best simulated antenna efficiency was 78.7%, the return loss was -33.91 dB and the VSWR was 1.041. Not all these simulated values have been proven experimentally through measurements due to insufficient equipment at the moment of performing the experiments. However, the three types of antennas were evaluated in the radia-tion chamber for their polarizaradia-tion and these measurement results are very close to the equivalent simulation results.
1. Introduction 1 1.1 Purpose . . . 1 1.2 Background . . . 1 2. Antenna parameters 3 2.1 Reflection coefficient . . . 3 2.2 Return loss . . . 3
2.3 Voltage Standing Wave Ratio . . . 3
2.4 Radiation Efficiency . . . 4
2.5 Antenna Polarization . . . 4
3. Methodology 5 3.1 Antenna design limitations . . . 5
3.2 Antenna substrate . . . 5
3.3 Patch antenna . . . 6
3.3.1 Patch antenna equations . . . 7
3.3.2 Simulation . . . 9
3.4 Inverted-F antenna . . . 10
3.4.1 Simulation Results . . . 12
3.5 Meandered inverted-F antenna . . . 14
3.5.1 Simulation . . . 14 4. Result 17 4.1 Antennas . . . 17 4.2 Measurement setup . . . 18 4.3 Measurement Results . . . 20 4.3.1 Patch antenna . . . 20 4.3.2 Inverted-F antenna . . . 21
4.3.3 Meandered Inverted-F antenna . . . 23
5. Discussion 26
6. Conclusion 29
iii
TERMS AND DEFINITIONS
EDA Electrical Design Automated
ADS Advanced Design System (Simulation Software)
PCB Printed Circuit Board
VSWR Voltage Standing Wave Ratio
IFA Inverted-F Antenna
MIFA Meandered Inverted-F Antenna
W Width
L Length
h height
c Speed of light
f0 operation frequency
ǫr Relative dielectric constant
ǫef f Effective dielectric constant
λ Wavelength Ω Ohm R Distance DC Direct Current RF Radio Frequency dB Decibel
1.
INTRODUCTION
Technology is advancing fast towards smaller components with maintained or better efficiency through innovative new methods that combines components and makes the module more dense. However, when size is not the biggest issue, one can still argue that bigger components are just as beneficial, or even better, for obtaining equal results in order to lower manufacturing cost.
The research group ComElec at ITN, Linköping University is building a position-ing network for hospital equipment and is currently usposition-ing Antenova A5645 (chip antenna) at 2.4 GHz.[5] Chip antennas are expensive and ComElec wants to re-duce cost but maintain performance. This thesis work compares a chip-antenna against three types of individually PCB antennas of limited area. After studying and simulation of the selected antenna types, some other designs were selected for manufacturing, real-life testing and comparison with the previously mentioned chip-antenna. The aim was to determine if it is possible to manufacture a PCB antenna within the given area limitations with equal, or better, performance than those of the chip-antenna.
1.1
Purpose
The purpose of this thesis is to design, simulate and manufacture at least one PCB antenna and compare it to a specified chip-antenna, Antenova A5645. For this to be a successful thesis at least one of the antennas should have equal or better performance than the chip antenna. Reference values for the Antenova A5645 are displayed in Table 3.
1.2
Background
In order to establish any form of wireless electrical connection, antennas are required in each end of the system. An antenna is basically a conductor exposed in space, an electrical component that converts electrical power into radio waves and vice versa. For a receiving antenna, the oscillating electromagnetic field of an incoming radio wave affects the electrons in the antenna elements, thus creates oscillating currents in the antenna. Antennas have a wide spectrum of usage, from short wave walkie-talkies to ultra wide broadband transceivers. An antenna is what can be called an
1. Introduction 2
application specific component. This means that it is designed for a specific type of transmission or receiving frequencies. For an antenna to be an efficient radiator its length must be at least comparable with its desired frequency of operation.[4] To understand the thesis and the design aspects of an antenna, literature recom-mended by the supervisor was studied. The intention is to learn how an antenna actually works, is designed for the given specifications and which mathematical ex-pressions are necessary for the task at hand [1][2][3].
The research group in Communication electronics, ComElec at ITN, Linköping University has implemented a positioning network for hospital equipment and is currently using Antenova A5645 at 2.4 GHz. Chip antennas are expensive and the group is interested in reduce costs but maintain performance.
After some consideration, the antennas chosen to analyze and design were; the monopole patch antenna, the F antenna (IFA) and the meandered inverted-F antenna (MIinverted-FA). These antennas were recommended in the thesis proposal. They are cheap to manufacture and have proven to have good efficiency during other projects. Moreover, the choice of these antennas is very useful and well suited to the better understanding of the antenna subject from operation to design and mea-surements.
The patch antenna was chosen because of its simpleness and for the fact that it could be physically implemented on a PCB board at the available facilities at ITN, LiU. Because of this feature it was also taken into consideration that the patch an-tenna would only be radiating in one direction, which could have an effect on the efficiency of the antenna. The IFA and MIFA were chosen because of the recom-mendation from the thesis proposal and also for the fact that they, similar to the patch antenna, can be manufactured at LiU. One distinct feature from the patch antenna is that the IFA and MIFA are placed in conjunction with the ground plane connected with a ground stub. This feature allows the antenna to radiate in a 360◦
radius, which can be useful due to the device being moved around as opposed to its connection gateway.
2.
ANTENNA PARAMETERS
This section briefly describes some important theoretical parameters that are used in this thesis.
2.1
Reflection coefficient
The reflection coefficient, denoted by gamma(Γ) or S11, determines the mismatch between the antenna and the system. It can be calculated from the values of the complex load impedance and the transmission line characteristic impedance which in principle could also be a complex number.
Γ = Z0− ZL Z0+ ZL
(2.1) Note that the magnitude of the reflection coefficient does not depend on the length of the line, only the load impedance and the impedance of the transmission line. The reflection coefficient value spans from -1 to 1 where -1 mean total reflection and all of the signal is reflected. The value 0 mean no reflection and that all of the power is transferred to the load [3].
2.2
Return loss
Return loss (RL) is defined as the amount of power which is reflected from the antenna. In other words, how much of the signal that is lost to the load and does not return as reflection [2]. Return loss is commonly displayed in decibel(dB) and determined by Equation 2.2.
RL(dB) = −20log|Γ| (2.2)
where the reflection coefficient Γ is defined in Equation 2.1.
2.3
Voltage Standing Wave Ratio
When electrical- or electromagnetical waves are propagating through circuits and, generally, through media, reflections might occur. The reflected waves combine with the incident waves resulting in standing waves determined by minimum and maxi-mum values of the voltage, current or fields. Voltage standing wave ratio(VSWR)
2. Antenna parameters 4
is defined as the ratio of the maximum voltage to the minimum voltage in standing wave pattern along the length of eg. a transmission line.
VSWR is determined using the reflection coefficient Γ, defined in Equation 2.1, and will always be a real and positive number [3]. The VSWR formula is displayed in Equation 2.3.
V SW R= 1 + |Γ|
1 − |Γ| (2.3)
When the reflection coefficient goes to zero, the VSWR is equal to one, which means that all of the applied power converts to radiated power. However, a rule of thumb is that a VSWR lower than three is fully acceptable in real-life-applications.
2.4
Radiation Efficiency
Efficiency is a measurement of how well a device converts one energy source to another. The higher the efficiency of the device, the less energy is lost in the con-version. Efficiency is often quoted as either percent (%) or decibels (dB) and it comes in many forms which focuses on efficiency from different aspects. Radiation efficiency is calculated with the formula displayed in Equation 2.4
eRad=
PRad
Pin
(2.4) where PRad is the power radiated from the antenna and Pin is the power applied to
the antenna [1].
2.5
Antenna Polarization
Polarization is one of the fundamental characteristics of any antenna, and refers to the the plane in which the electric field is oriented. Depending on its physical struc-ture and its orientation, the antenna polarization will have vastly different results. Thus, an antenna will have one polarization when mounted vertically and a different polarization when mounted horizontally.
The concept of polarization is important for antenna to antenna communication. It is important to notice the orientation of the antenna will have a great impact on the communication. For example, a vertically polarized antenna will not communicate with a horizontally polarized antenna, since antennas transmit and receive in exactly the same manner. Hence, a horizontally polarized antenna transmits and receives horizontally polarized fields, and vice versa. Thus, there will be next to no commu-nication if the transmitting and the receiving antenna is of different polarization. [1]
3.
METHODOLOGY
This chapter describes the design process of the antennas under investigation. The Electrical Design Automated(EDA) tool Advanced Design System (ADS) was used as the sole platform for building and simulating the antenna designs. The work focused on one antenna at the time. The work frequency for this project was specified to 2.4 GHz.
Before introducing the methodology one must first consider the antenna which this thesis is being compared to, the Antenova A5645. In Table 3 som values from the datasheet is summarized.
Table 3.1: Values for the Antenova A5645
Characteristics
Average Efficiency 65%
Maximum VSWR 1.8:1
Maximum Return loss -11dB
One must note that the Antenova A5645 has a frequency span from 2.4 GHz to 2.5 GHz, and the values in Table 3 are given over this span, and not specifically for 2.4 GHz which is the selected operation frequency for this project.
The polarization plots are found in the datasheet for the Antenova A5645. [2]
3.1
Antenna design limitations
It was a requirement that the total size of the antenna should have a maximum size of 30mm by 30mm. The total size includes the antenna itself as well as the attached ground plane. There are no lower limit, but through the theoretical study one can assume that the efficiency levels will decrease rapidly if the size of the antenna becomes small.
3.2
Antenna substrate
The substrate used for this project is a fire resistant material called FR-4. FR-4 is a fiberglass woven material that is embedded in epoxy resin. FR-4 is one of the most
3. Methodology 6
common substrate types upon which the majority of printed circuit boards (PCBs) are produced. FR-4 copper-clad sheets are fabricated with circuitry interconnections etched into copper layers to produce printed circuit boards. A thin layer of copper foil is laminated to one or both sides of an FR-4 glass epoxy panel.
In conjunction with a past course in RF electronics(TNE088), the dielectric constant for FR-4 used in this project is 4.6.
3.3
Patch antenna
The microstrip antenna, also known as a printed antenna or patch antenna, is ba-sically a transmission line which is mounted upon a grounded substrate. However, instead of finding the specifics for matching the microstrip, the specifics are designed in order to create resonance.
The patch antenna is the most popular type of microstrip antenna and it comes in many different forms and configurations. In this project the rectangular, single-polarized patch antenna will be discussed.
Figure 3.1: Patch antenna
A patch antenna, including definition for its length(L) and width(W) is shown in Figure 3.1 It was decided that the patch antenna were to be the first antenna to handle because of the existing theory behind it and its straight-forward design. In other words, a good introduction to the crafting of microstrip antennas. Basically, the patch antenna consist of three major parts; ground plane, the actual antenna and finally the microstrip transmission line. The microstrip transmission line often goes by the name power feed line, or simply feed line.
Advantages of microstrip antennas include: • Low cost to fabricate
• Conformal structures are possible (it’s easy to form curved surfaces, as long as the curve is in one plane only)
Disadvantages include:
• Limited bandwidth (usually 1 to 5%, but much more is possible with increased complexity)
• Low power handling
In this thesis, the top priority is the low cost and with as high antenna performance as possible. However, patch antennas have narrow frequency bandwidth which might make it difficult to design a patch antenna with the given specifications.
3.3.1
Patch antenna equations
Using Equations 3.1 - 3.11 for a patch antenna, calculations were made in order to find first value estimations för the width(w) and length(L) of the patch antenna for 2.4 GHz. These calculations were made without regard of the limitation of 30 x 30 mm2 ground plane. W = c (2 ∗ f0∗ q εr+1 2 ) (3.1) εef f = εr+ 1 2 + εr− 1 2 [1 + 12 h W] −12 (3.2) Lef f = c (2 ∗ f0∗ √ εef f) (3.3) ∆L = 0.412h(εef f + 0.3)( W h + 0.264) (εef f − 0.258)(Wh + 0.8) (3.4) L= Lef f − 2∆L (3.5) Z0 = η0 √ǫ ef f[wh + 1.393 + 2 3ln( w h + 1.444)] (3.6) Yin(z) = 2G cos2(βz) + G2+B2 Y0 sin 2 (βz)2 − B Y0 sin(2βz) (3.7) Zin(z) = Zin(0) cos 2 (πz l) (3.8) k0 = 2π λ0 (3.9) β = 2π λ = 2π√ǫef f λ0 (3.10)
3. Methodology 8
η0 =
r µ0
ǫ0
= 377Ω (3.11)
With 2.4 GHz as the operation frequency and the relative dielectric constant εr set
to 4.6. This gave the following result;
• W = 37.4 mm • L = 29 mm
The w and L values are the start point of the patch antenna design., Remained is the problem of the feed line. The practical solution to this is to attach a transmission line with 50Ω impedance to the input port of the patch antenna.
A second problem is that the calculated dimensions exceed the given limitations of 30 x 30 mm2
. From here on, an experimental search for a "good enough" patch antenna within the limitations started. In order to do this experimental search, two features in ADS called ’Parameter Sweep’ and ’Transient Sweep’ were used. These features basically allow the user to sweep over specific parameters which can be var-ied in different combinations in order to find a suitable size for the patch antenna. In this case, the parameters chosen to be swept were the length and width of the patch, and the depth of the feed line. The depth of the feed line is basically how far into the patch that the feed connects to the antenna. This is done in order to match the edge impedance of the antenna to the feed line.
There is one major flaw with this method, time. Using sweeps for different pa-rameters result in long ADS run-times. In the end, this approach of good-enough did work out poorly and the patch antenna within the limitations was put aside. In order to still have a patch antenna, the patch antenna based of the theoreti-cally estimated values of w and L was designed. The thought process was that It was considered worth to have a reference design of a patch antenna. After some experimentation the result became the following:
Figure 3.2: Layout view of the patch antenna
Figure 3.2 shows a patch antenna which occupies a larger area than the specified limitation of 30 x 30 mm2
, and is closer to the calculated values from theory. Even though the simulation results are not ideal, its purpose to act a reference is fulfilled.
3.3.2
Simulation
The simulation results from the patch antenna are presented in Figures 3.3 and 3.4. In 3.3, the frequency response in shown.
2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 Frequency(Hz) ×109 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 Magnitude(dB) X: 2.4e+09 Y: -16.76
Figure 3.3: Frequency response of the patch antenna: |S11| 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 Frequency(Hz) ×109 0 10 20 30 40 50 60 70 80
Voltage standing wave ratio(VSWR)
X: 2.4e+09 Y: 1.34
Figure 3.4: VSWR plot for the patch an-tenna
3. Methodology 10
Figure 3.5: Polarization plot of the patch antenna
In Figure 3.4, the simulation results show a VSWR of 1.34 and a acceptable attenuation of -16.76 dB. In Figure 3.5, the polarization plot of the simulated patch antenna is shown. This will be used as a comparison against the manufactured patch antenna.
3.4
Inverted-F antenna
A second antenna type that will be analyzed and designed is the inverted-F antenna. The inverted-F antenna, shortened IFA, is an evolved type of a standard monopole antenna which is popular in wireless communication. It consists of a monopole antenna running parallel to a ground plane. The antenna is grounded at one end and fed from an intermediate point at a specific distance from the grounded end. The feed is placed from the ground plane to the upper arm of the IFA.
Figure 3.6: Reference picture of inverted-F antenna
In comparison to a regular monopole antenna, the inverted-F has some distinct advantages. The antenna is shorter, more compact and the impedance matching can be controlled by the designer without the need for matching components. The upper arm of the IFA has a length that is roughly a quarter of a wavelength. Since there are no specific equations on how to create an Inverted-F antenna, the designs were created through experiment directly in ADS. The foundation for this was taking a microstrip line with 50 Ω impedance with a length of roughly a quarter of a wavelength and putting it together with a feed line and a stub connected to a ground plane. From here on, virtual experimentats in ADS were made to alter the design in order to get a desired simulation result.
Because the patch is shorted at the end, the current at the end of the patch an-tenna is no longer forced to be zero. As a result, this anan-tenna actually has the same current-voltage distribution as a half-wave patch antenna. However, the fringing fields which are responsible for radiation are shorted on the far end, only the fields nearest the transmission line radiate. Consequently, the antenna gain is reduced, but the patch antenna maintains the same basic properties as a half-wavelength patch, but is reduced in size.
3. Methodology 12
Figure 3.7: Layout view of the wider IFA Figure 3.8: Layout view of the narrower IFA
Figure 3.7 and Figure 3.8 show the final layout of the two inverted-F antennas. Figure 3.7 show an IFA designed with a maximum size ground plane. Figure 3.8 show an IFA with a smaller ground plane to investigate the difference.
3.4.1
Simulation Results
For simplicity when referring to the different antennas they will be called IFA-1 and IFA-2, where IFA-1 refer to the larger antenna and IFA-2 refer to the smaller version of and inverted-F antenna.
The simulation results are shown in Figures 3.9 to 3.12:
Figure 3.9: Frequency respone of IFA-1: |S11|
Figure 3.11: Frequency respone of IFA-2: |S11|
Figure 3.12: VSWR of the IFA-2
Figures 3.9 and 3.11 show the frequency responses of the two antennas in terms of |S11|. They predict that the antenna will operate at the frequencies around 2.4 GHz
Figures 3.10 and 3.12 show the VSWR of the IFA’s. Polarization plots for the inverted-F antenna are presented in Figures 3.13 and 3.14:
Figure 3.13: Polarization plot of IFA-1 Figure 3.14: Polarization plot of IFA-2 Figure 3.9, 3.10, 3.11, and 3.12 show that even though the antennas are similar, the result is quite different. IFA-1 has a larger bandwidth but lower attenuation aswell as a slightly higher VSWR. IFA-2 is narrow in bandwidth, similar to the patch antenna, and the VSWR is very close to ideal.
3. Methodology 14
3.5
Meandered inverted-F antenna
The meandered inverted-F antenna is another type of antenna that is frequently used in many wireless communication types. The MIFA is basically a progression of the standard inverted-F antenna. In order to save space but keep the performance, one came up with the idea to "fold" the transmitting arm. With this comes a few more variables to consider during design, in addition to the variables mentioned in Section 3.4 such as the capacitance between each fold.
Figure 3.15: Layout view of the wider MIFA
Figure 3.16: Layout view of the narrower MIFA
Both of the MIFA’s is similar in shape and the number of folds. It was tried multiple times to make the antennas more unequal, but there were not any successful simulations.
3.5.1
Simulation
For simplicity when referring to the different antennas they will be called MIFA-1 and MIFA-2, where MIFA-1 refer to the larger antenna and MIFA-2 refer to the smaller version of and inverted-F antenna.
Figure 3.17: Frequency respone of MIFA-1: |S11|
Figure 3.18: VSWR of MIFA-1
Figure 3.19: Frequency respone of MIFA-1: |S11|
Figure 3.20: VSWR of MIFA-2
Figures 3.21 and 3.22 present the polarization plots for the meandered inverted-F antennas:
3. Methodology 16
Figure 3.21: Polarization plot of MIFA-1 Figure 3.22: Polarization plot of MIFA-2 As expected, the simulations for 1 and 2 and very similar. MIFA-1 has a bit better VSWR but also has more narrow bandwidth. Also, both of the antennas has their magnitude peak a few MHz off from the intended working frequency 2.4GHz.
4.
RESULT
This Section shows the antennas achieved after manufacturing in the PCB laboratory and testing in the radiation chamber. After the design in ADS, Gerber files were generated. Using the facilities offered by the PCB lab at LiU, the antennas were manufactured. The prototypes are shown in Figures 4.1 to 4.5.
All antennas are manufactured with FR-4 substrate
4.1
Antennas
This displays the manufactured antennas soldered with an SMA contact.
4. Result 18
Figure 4.2: Manufactured 2.4 GHz IFA, wide arm (IFA-1)
Figure 4.3: Manufactured 2.4 GHz IFA, narrow arm (IFA-2)
Figure 4.4: Manufactured 2.4 GHz MIFA, wide arm (MIFA-1)
Figure 4.5: Manufactured 2.4 GHz MIFA, narrow arm, (MIFA-2)
4.2
Measurement setup
Each test were made by mounting the antenna onto a platform which rotated from -180◦ to 180◦ in order to span over 360◦. The antenna was connected to a Vector
then transmitted the data to the VNA for display.
Figure 4.6: Simple sketch of measurement setup
In the radiation chamber two types of measurements were made. Impedance matching and polarization. For the polarization measurements, four different se-tups were used in order to be as thorough as possible. Polarization measurements were done with the antenna in horizontal and vertical position. Additionally, the receiver was used in 0◦ and 90◦ rotation.
4. Result 20
Figure 4.7: Front view of setup Figure 4.8: Above view of setup Figure 4.7 shows the setup from behind, with the antenna pointing 180 ◦ from
the receiver. The receiver is seen in the back. Figure 4.8 shows how the antenna was mounted in the vertical position. For the horizontal measurements, the antenna was mounted by fixating the cable through the plastic, thus leaving the antenna in the correct position.
4.3
Measurement Results
This Section presents the resulting polarization plots for each antenna when mea-sured in the radiation chamber.
4.3.1
Patch antenna
Results from measurements of the manufactured patch antenna. Receiver in starting position, turned 0◦.
0° 15° 30° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.9: Polarization plot of vertical position 0° 15° 30° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.10: Polarization plot of hori-zontal position
Receiver in second position, turned 90◦.
0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.11: Polarization plot of verti-cal position 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.12: Polarization plot of hori-zontal position
4.3.2
Inverted-F antenna
Results from measurements of the manufactured F antennas. The inverted-F antenna was made in two copies with different size and shape. inverted-For easy reference, the antenna with the narrower arm will be called IFA-1, and the wider IFA-2. The result for IFA-1: Receiver in starting position, turned 0◦.
4. Result 22 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.13: Polarization plot of vertical position 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.14: Polarization plot of hori-zontal position
Receiver in second position, turned 90◦.
0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.15: Polarization plot of vertical position 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.16: Polarization plot of hori-zontal position
0° 15° 30° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.17: Polarization plot of vertical position
Since the IFA antennas are very similar, it was concluded that it was important to do thorough measurements for only one of the inverted-F antennas. This was motivated since it is the same antenna type and that thorough measurements for both antennas would give minor differences. Thus, thorough measurements were done for IFA-1, and only a vertical measurement was done for IFA-2.
4.3.3
Meandered Inverted-F antenna
Results from measurements of the manufactured Meandered inverted-F antenna are presented in 4.3.3. The meandered inverted-F antenna was made in two copies with the same ground plane but different arm size and shape. For easy reference, the antenna with the narrower arm will be called MIFA-1, and that with wider arm MIFA-2.
4. Result 24 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.18: Polarization plot of vertical position 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.19: Polarization plot of hori-zontal position
Receiver in second position, turned 90◦.
0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.20: Polarization plot of vertical position 0° 15° 30° 45° 60° 75° 90° 105° 120° 135° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.21: Polarization plot of hori-zontal position
0° 15° 30° 150° 165° ±180° -165° -150° -135° -120° -105° -90° -75° -60° -45° -30° -15° -8 -6 -4 -2 0
Figure 4.22: Polarization plot of vertical position
As the two MIFAs are very similar, measurements were done only for one of these. The antennas are of the same type. Moreover, the MIFA’s are of similar size and shape, which suggest that the results should not differ greatly and that further measurements is unnecessary.
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5.
DISCUSSION
This thesis concludes that PCB antennas are, although not an ideal choice, a reason-able substitute for a chip antenna if there is enough room in order to decrease cost. Due to lack of time, the antennas could not be fully tested after manufacturing. Each antenna was designed and simulated adopting a specific order from patch an-tennas to meandered inverted-F anan-tennas.
After acquiring antenna theory knowledge, including the types of antennas and antenna parameters the design work was started. The existing theory for the patch antenna gave a good platform which served as introduction to antennas. There are equations which states clearly how to find the proper size of the patch if the designer knows the substrate material and operation frequency. As stated, the calculated val-ues for the optimal size patch antenna exceeded the specified dimensions. However, it was considered of worth to design and manufacture the patch antenna.
For the inverted-F antenna and the meandered inverted-F antenna there are no analytical models i.eg. equations to permit first hand calculation of the antenna geometrical dimensions. Instead, one had to use RF knowledge in order to find the expected result. This means taking into account wavelength, size of the transmit-ting arm, placement of the feed line, and capacitance between ground plane and the transmitting arm etc. In order to find a reasonable result from these antenna types, much of the design and simulation work was more of an experimental approach. Trying different variations, shapes and forms finally gave two results for both the inverted-F and the meandered inverted-F antennas. Although they are similar in size, when measured upon they gave different results.
Before manufacturing, each of the antennas had their initial design altered in order to be able to attach the SMA contact to the PCB. This was done by attaching a 50 Ω microstrip line to the fed line end point, extending the feed by some length. Also, the pin of the SMA contact which was soldered to the antenna in order to connect to the feed line contributed with elements that deviate from the simulation results. In addition, there are other factors that affects the antenna performance such as sta-tistical variation in the manufacturing process, e.g. quality of manufacturing gear,
After manufacturing, each antenna was tested in a radiation chamber. Unfortu-nately, the instruments were calibrated for polarization plots and not for the explicit parameters that were given from the datasheet of the chip antenna.
When looking at the simulation results and comparing them to the Antenova A5645 parameters, it can be said that the designed antennas are are close to the chip antenna parameters. The comparison is summarized in Table 5.1:
Table 5.1: Values for the Antenova A5645
Antenna Efficiency Return Loss VSWR
Antenova A5645 65% -11dB 1.8:1 Patch antenna 44.1% -16.758dB 1.340:1 IFA-1 78.7% -33.91dB 1.041:1 IFA-2 74% -15.236dB 1.419:1 MIFA-1 75.7% -9.235 2.055:1 MIFA-2 78.5% -8.456 2.205:1
As seen in Table 5.1, four of the antennas are exceeding the Antenova in terms of efficiency. However, one should keep in mind that the value for the chip antenna is an average value and not the peak value as for the designed antennas. The peak value for the Antenova is for 2.45 GHz, meaning that the average value is a bit mis-leading. Additionally, the average values for the chip antenna is measured in "good environment" on a reference board measured value. Whereas for the designed an-tenna the values are from the simulated models.
This thesis has handled the design of antennas at 2.4 GHz. The only restrictive specification was the permitted area, which the rest of antenna parameters were targeted to the best achievable in this work. Under other time limitations and more specific limitations given for the thesis work, the project has however shown that custom-designed antennas can achieve commercial antenna performance. Further work is thus encouraged by the results presented in this thesis.
Analyzing the return loss, the inverted-F antennas exceed the performance of the chip antenna.. The IFA’s still exceed the chip antenna, but the MIFA’s does not. This might be depending on the layout of the MIFA. This could be because a curved arm has more capacitive contributions, which forces an increase in the inductive ele-ment in order to keep balance. This might lead to a point where reflection increases due to mismatch in any of the two parts, thus increasing the loss in the antenna.
5. Discussion 28
Finally, looking at the VSWR for each antenna the IFA’s are showing a VSWR well below 1.8:1, but the MIFA’s are exceeding the value. However, as earlier stated, a rule of thumb is that a VSWR below 3:1 is considered good when manufactured. With that in mind it can be considered that both antennas present good results. With better planning, the experimental search for a patch antenna below 30x30mm could have ended sooner and the thesis could have made a better progress and thus leaving more time to design the remaining antennas. If more time had been spent on the latter, perhaps an even better antenna could have made its way to manu-facturing. However, looking back at the results, there are results implying that an antenna which are on pair with the Antenova A5645 is within reach.
As we look back upon the results there one should make the conclusion that based of the simulation results there is a good chance that one of the models can have equal or better performance than the Antenova A5645. However, that it just speculations and must be tested thoroughly before stating it as definite.
6.
CONCLUSION
In this thesis work, several antenna designs and their implementations are presented. The antennas were Patch antenna, Inverted-F antenna and Meandered Inverted-F antenna. They were designed for operation frequency at 2.4 GHz.
Firstly, the antenna were designed in ADS. Simulation results were evaluated and compared to Antenove A5645, a commercial antenna. The simulation results were compared with the reference antenna. To more accurately characterize the antenna designs, they were manufactured and tested. As compared to simulation results, the measured parameters presented differences that can be explained through a variety of causes, e.g. statistical variation of the geometrical parameters and other kind of variety due to the manufacturing process. To succeed, further design work is necessary. However, this thesis work demonstrates the need of custom-designed antennas for lower-cost when other antenna parameters are secondary.
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REFERENCES
[1] Vincent F. Fusco, Antenna Theory and Techniques, Pearson, 2005
[2] David M. Pozar, Microwave and RF design of wireless systems, Pearson, 2005 [3] R. Ludwig et al, RF Circuit Design - Theory and Applications 2nd ed
[4] Antenna Fundamentals (2016, June 20). Antenna Basics. Retrieved from http://www.antenna-theory.com/basics/main.php
[5] Antenova Ltd, Antenova A5645, Datasheet: http://www.antenova-m2m.com/wp-content/uploads/2015/11/Mica-A5645-PS-1.11.pdf
