Lightweight Silver Ink Printed Circular Ring Microstrip Patch

LIGHTWEIGHT SILVER INK PRINTED CIRCULAR RING
MICROSTRIP PATCH ANTENNA FOR WLAN APPLICATIONS
by
Bobak Beheshti
Senior Project
ELECTRICAL ENGINEERING DEPARTMENT
California Polytechnic State University
San Luis Obispo
2015
i
TABLE OF CONTENTS
TITLE PAGE ................................................................................................................................................ i
TABLE OF CONTENTS ............................................................................................................................. ii
LIST OF TABLES ...................................................................................................................................... iii
LIST OF FIGURES .................................................................................................................................... iv
ABSTRACT ................................................................................................................................................. 1
I. INTRODUCTION .................................................................................................................................... 2
II. SYSTEM REQUIREMENTS AND SPECIFICATIONS ........................................................................ 6
III. SYSTEM DESIGN AND ANALYSIS ................................................................................................... 7
IV. SYSTEM TESTING AND RESULTS ................................................................................................. 14
V. CONCLUSION ...................................................................................................................................... 20
VI. BIBLIOGRAPHY ................................................................................................................................ 21
APPENDICES
A. PARTS LIST AND COSTS ...................................................................................................... 22
B. ANALYSIS OF SENIOR PROJECT DESIGN ........................................................................ 23
ii
LIST OF TABLES
Table I: WLAN Operating Frequency Ranges and Applications ................................................................. 2
Table II: Circular Ring Patch Antenna Percentage Bandwidth Relative Factors ......................................... 4
Table III: Circular Ring Patch Antenna Specifications ................................................................................ 6
Table IV: Circular Ring Patch Antenna Design Parameters ........................................................................ 7
Table V: HFSS Circular Ring Patch Antenna Physical Dimensions ............................................................ 8
Table VI: HFSS Circular Ring Patch Antenna Electrical Dimensions.......................................................... 8
Table VII: Measured Circular Ring Patch Antenna |S11| (dB) at WLAN Frequencies ............................... 16
Table VIII: Circular Ring Patch Antenna Materials and Costs .................................................................. 22
Table IX: Circular Ring Patch Antenna Single Unit vs. Bulk Materials and Costs ................................... 24
iii
LIST OF FIGURES
Figure 1: HFSS Circular Ring Patch Antenna Model, Radii = 27.9mm and 59mm, Copper Substrate,
Silver Patch (Top View) ................................................................................................................................ 3
Figure 2: HFSS Circular Ring Patch Antenna Model, Length and Width = 123.9mm (Bottom View) ....... 3
Figure 3: HFSS Circular Ring Patch Antenna Model (Side View) Inner Conductor to Patch (Left) and
Outer Conductor to Ground (Right) ............................................................................................................. 4
Figure 4: Receiving Circular Ring Patch and Transmitting Horn Antenna Co-Pol Test Setup..................... 7
Figure 5: HFSS Circular Ring Patch Antenna Model (Top View) ................................................................ 9
Figure 6: HFSS Circular Ring Patch Antenna Probe Feed ........................................................................... 9
Figure 7: HFSS Circular Ring Patch Antenna |S11| (dB) vs. Frequency (GHz) without DGS .................... 10
Figure 8: HFSS Circular Ring Patch Antenna Model with DGS ............................................................... 10
Figure 9: HFSS Circular Ring Patch Antenna |S11| (dB) vs. Frequency (GHz) with DGS ........................ 11
Figure 10: HFSS Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB), f = 2.4GHz,
φ = 90°, 180° < θ < 180° ............................................................................................................................ 11
Figure 11: HFSS Circular Ring Patch Antenna Directivity (dB) vs. Frequency (GHz), f = 2.4GHz ........ 12
Figure 12: HFSS Circular Ring Patch Antenna Directivity Radiation Pattern (dB), f = 2.4GHz,
φ = 90°, -180° < θ < 180° (Above Patch) .................................................................................................. 12
Figure 13: HFSS Circular Ring Patch Antenna Directivity Radiation Pattern (dB), f = 2.4GHz,
φ = 90°, -180° < θ < 180° (Below Patch) ................................................................................................... 13
Figure 14: Circular Ring Patch Antenna (Top View) ................................................................................. 14
Figure 15: Circular Ring Patch Antenna (Bottom View) ........................................................................... 14
Figure 16: Test Fixture Mounted Circular Ring Patch Antenna in Anechoic Chamber ............................. 14
Figure 17: HFSS Coordinate Axes for Test Fixture Mounted Circular Ring Patch Antenna with Probe
Feed ............................................................................................................................................................ 15
Figure 18: Measured Circular Ring Patch Antenna |S11| (dB) vs. Frequency (GHz) ................................. 15
iv
Figure 19: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB), f = 2.4GHz,
φ = 90°, -180° < θ < 180° .......................................................................................................................... 16
Figure 20: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB), f = 2.7GHz,
φ = 90°, -180° < θ < 180° .......................................................................................................................... 17
Figure 21: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB), f = 3.1GHz,
φ = 90°, -180° < θ < 180° .......................................................................................................................... 17
Figure 22: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB), f = 4.6GHz,
φ = 90°, -180° < θ < 180° .......................................................................................................................... 18
Figure 23: HFSS vs. Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB),
f = 2.4GHz, φ = 90°, -180° < θ < 180° ...................................................................................................... 18
v
ABSTRACT
Wireless communications systems include the internet, mobile phones, navigation, public safety
and industrial processes. Many of these applications are managed under IEEE 802.11 WLAN (wireless
local area network) protocols. WLAN connects communication devices over a short range (< 100m) and
includes 2.4-5GHz bands.
This paper presents a probe fed planar microstrip patch antenna design for 2.4-5GHz WLAN
applications. Compact and lightweight antennas are favored for applications involving portable
electronics such as laptops. Directional antennas receive stronger signals from a signal source at a known
location, e.g. a laptop antenna and a router, than omnidirectional antennas. A planar microstrip patch
antenna is directional (between 5dB and 8dB) and can be flush mounted on flat surfaces. Developing
patch antennas with exceptionally thin (< 0.003λ) substrates allow users to mount a lighter, more compact
antenna to many portable devices. However, exceptionally thin substrates (thickness h < 0.003λ) decrease
impedance bandwidth.
Circular ring patch antennas exhibit up to twice the impedance bandwidth of similarly sized
generic rectangular patch antennas. A circular ring patch is designed for 2.4GHz operation with inner and
outer radii of 1.090” and 2.320”, respectively. DGS (defected ground structure), formed by partially
removing the ground plane, widens impedance bandwidth by increasing ground plane current distribution
and decreasing shielding to increase electromagnetic wave propagation in the substrate. A 1mm radius
circular ring DGS is formed by removing the ground plane around the probe feed location, yielding an
UWB (ultra-wideband) receiving antenna.
The circular ring patch is modeled using Ansys HFSS (High Frequency Structural Simulator).
The patch is screen printed using conductive silver ink, a process performed in the Cal Poly Graphic
Communications Special Resources Laboratory, and the ground plane is constructed with copper adhesive
tape to afford relative ease of creating and modifying the DGS. The Cal Poly Electrical Engineering
Department’s Microwave Laboratory and anechoic chamber with vector network analyzers and Labview
AMS (Antenna Measurement System) software are used for antenna testing.
The fabricated antenna achieves a 20dB return loss bandwidth from 2.313-5.550GHz, wider than
the target 2.4-5GHz bandwidth. The simulated radiation pattern at 2.4GHz has maximum 5.7dB
directivity above the patch and 1.4dB directivity below. The fabricated patch antenna’s radiation pattern
above the patch has maximum 7.1dB directivity, an improvement relative to the simulation.
1
I. INTRODUCTION
Table I: WLAN Operating Frequency Ranges and Applications
Frequency (GHz)
2.412-2.462
Description
802.11b/g/n; Wi-Fi internet, Bluetooth, Zigbee, majority of consumer
applications.
3.658 -3.693
802.11a; Industrial controls.
5.180-5.825
802.11a/ac/n; Public safety resources, additional bandwidth for 2.4GHz
applications.
Table I lists IEEE 802.11 WLAN operating frequency ranges requiring less than 100m distance
range at low power [1]. The 2.4GHz band is used for internet, Bluetooth and Zigbee. Bluetooth enables
communication between mobile phones or computers to peripheral devices, automatic device
synchronization and home controls. Zigbee uses wireless networks in which all nodes are utilized to relay
information and in home and building controls. The 3.7GHz band is reserved for industrial controls such
as industrial Bluetooth and Zigbee. Industrial Bluetooth automates manufacturing and connects
manufacturing facility sectors to remote locations and industrial Zigbee self-guides vehicles, monitors
energy and connects proprietary radios for industrial equipment communication. The 5GHz frequency
band allocates 5.180-5.825GHz for 2.4GHz Wi-Fi applications and enables public safety applications
such as surveillance, emergency communications and security networks.
Many of these WLAN applications are mobile. A portable, mountable and directional antenna
with low power consumption is favorable. Planar microstrip patch antennas fulfill the criteria listed.
Patch antennas include two planar conductive materials, a radiating patch on top and ground plane
underneath, separated by a dielectric substrate. Figure 1 and Figure 2 display a probe fed planar
microstrip patch antenna’s top and bottom views respectively. Figure 1 shows the radiating ring patch on
a substrate with a probe feed. Figure 2 shows the ground plane and coaxial probe feed with a concentric
annular ground defect around the probe feed. Figure 3 shows the coaxial probe feed’s outer and inner
conductors, connected to the ground and patch respectively depicted as cylinders connected to the top
patch on the left patch antenna and bottom ground plane on the right patch antenna.
2
Figure 1: HFSS Circular Ring Patch Antenna Model, Radii = 27.9mm and 59mm, Copper Substrate, Silver Patch (Top
View)
Figure 2: HFSS Circular Ring Patch Antenna Model, Length and Width = 123.9mm (Bottom View)
3
Figure 3: HFSS Circular Ring Patch Antenna Model (Side View) Inner Conductor to Patch (Left) and Outer Conductor to
Ground (Right)
The typical patch antenna substrate thickness h is between 0.003λ and 0.050λ (15mil to 246mil at
2.4GHz). A patch antenna for which h < 0.003λ is considered an electrically thin antenna. Decreasing
substrate thickness h decreases percentage bandwidth %BW as follows, where w and l are patch antenna
width and length respectively and A is the proportionality constant:
% =
ℎ
λ0 √ε

√
(1)
Equation (1) expresses direct proportionality between h and %BW and Table II shows possible
values of A in terms of other factors in (1) [2]:
Table II: Circular Ring Patch Antenna Percentage Bandwidth Relative Factors

 √
A
≤ 0.045
180
≤ 0.075
200
≥ 0.075
220
The patch is printed on 14mils thick 100% PET (polyethylene terephthalate), a lightweight plastic
(εr = 3.2). Equation (1) demonstrates that the use of a thin substrate necessitates design approaches which
focus on impedance bandwidth improvement.
4
Bergman and Schultz originally proposed the popular circular ring patch antenna in 1955 as a
wideband radiator [3]. DGS, created by deliberately removing a portion of the ground plane and exposing
the substrate, widens impedance bandwidth by breaking ground plane current shielding, resulting in the
excitation of electromagnetic waves. DGS reportedly achieves UWB performance and can potentially
access all 2.4-5GHz WLAN frequency bands [4].
5
II. SYSTEM REQUIREMENTS AND SPECIFICATIONS
Table III: Circular Ring Patch Antenna Specifications
Specifications
Justification
Substrate height h < 0.003λ
Substrate is thinner than typical patch antenna
substrates.
Nominal 50 driving point impedance
Impedance is matched to 50 coaxial connector.
Minimum 20dB return loss from 2.4-5GHz
Operating bandwidth includes 2.4-5GHz WLAN
frequency bands.
Directional radiation pattern: 5dB < DdB < 8dB
toward user direction
Portable applications receive stronger radiation
directed towards the user. Typical patch antennas
exhibit between 5dB and 8dB directivity [5].
HPBW (H-plane):  < 360°
Omnidirectional in H-plane.
 =
HPBW (E-plane): 18.205° <  < 36.237°
41,253
 
(2)
3.162 <  < 6.310
Equation (2) relates directivity to HPBW (E-plane) [5].
Table III summarizes project specifications. DdB is the main lobe (directional part of radiation
pattern containing max radiated power) max directivity (max power density in direction of max radiated
power). HPBW (half-power beamwidth) is the angular separation between two points where power
measures 3dB lower than the max radiated power.
6
III. SYSTEM DESIGN AND ANALYSIS
Figure 4: Receiving Circular Ring Patch and Transmitting Horn Antenna Co-Pol Test Setup
Figure 4 illustrates the vertically polarized antenna under test and E-plane (YZ) and H-plane
(XZ). A broadband, directional and linearly polarized horn antenna transmits. The circular ring patch
antenna’s y-axis aligned probe feed results in the corresponding E-plane orientation.
Table IV: Circular Ring Patch Antenna Design Parameters
Parameter
Value
Description
11
2.4GHz
Resonant frequency for dominant TM11 mode
ɛr
3.2
PET dielectric constant
 =
′ 
2
(3)
1.841
11 √ɛ
= 20.460
(4)
 = 2
0.350 >
 −
 +
→  < 42.490
(5)
7
Table IV defines design parameters for a PET substrate at 2.4GHz resonant frequency. Equation
(3) defines TMmn mode circular ring patch resonant frequencies based on the uniform circular loop patch
cavity model [6]. ′ is the zero of the mth derivative Bessel function Jm(x) for mode TMmn, c is the
speed of light in a vacuum and ri and ro are the circular ring patch inner and outer radius. Equations (4)
and (5) define conductive patch inner and outer radii, respectively, assuming dominant TM11 mode [3].
HFSS optimization indicates greatest return loss occurs using ri = 27.600mm (4.53λ and circumference
173.410mm) with outer radius ro = 59.000mm (2.120λ and circumference 370.700mm). Probe feed
radius and center HFSS optimization determines the probe feed location at (0.000mm, 51.200mm,
0.000mm). Table IV lists antenna width and height RSize, antenna thickness ZSize and probe feed and
circular ring patch inner and outer radii Radius.
Table V: HFSS Circular Ring Patch Antenna Physical Dimensions
Structure
RSize
[mm]
ZSize
[mm]
Radius
[mm]
Center (X, Y, Z) [mm]
Inner Ring
-
-
27.600
0.000, 0.000, 0.000
Outer Ring
-
-
59.000
0.000, 0.000, 0.000
Substrate
123.900
0.360
-
0.000, 0.000, 0.000
Ground
123.900
0.000
-
0.000, 0.000, 0.000
Probe Feed
-
0.360
0.700
0.000, 51.200, 0.000
Table VI: HFSS Circular Ring Patch Antenna Electrical Dimensions
Structure
RSize [λ]
ZSize [λ]
Radius
[λ]
Center (X, Y, Z) [λ]
Inner Ring
-
-
4.530
0.000, 0.000, 0.000
Outer Ring
-
-
2.120
0.000, 0.000, 0.000
Substrate
1.010
351.500
-
0.000, 0.000, 0.000
Ground
1.010
0.000
-
0.000, 0.000, 0.000
Probe Feed
-
351.500
178.600
0.000, 2.440, 0.000
8
Figure 5: HFSS Circular Ring Patch Antenna Model (Top View)
Figure 6: HFSS Circular Ring Patch Antenna Model Probe Feed
Tables V and VI summarize HFSS specifications. Figure 5 shows the HFSS patch antenna model
top view with coordinate axes. Figure 6 shows the Probe Feed within the substrate.
9
Figure 7: HFSS Circular Ring Patch Antenna |S11| (dB) vs. Frequency (GHz) without DGS
Figure 7 shows |S11| vs. frequency from 1.5GHz to 3.5GHz without DGS. Return loss simulations
verify 54.508dB 50 impedance matching at the 2.4GHz resonant frequency.
Figure 8: HFSS Circular Ring Patch Antenna Model with DGS
Figure 8 shows the simulated 1mm radius annular ground defect’s location on the ground plane.
The coaxial inner and outer conductors connect to the patch and ground plane, respectively.
10
Figure 9: HFSS Circular Ring Patch Antenna |S11| (dB) vs. Frequency (GHz) with DGS
Figure 9 demonstrates the effect of a 1mm radius annular ground defect centered at the probe feed
position and shows that resonance shifts from 2.4GHz to 2.3GHz while return loss increases within higher
frequency bands.
Figure 10: HFSS Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB), f = 2.4GHz,
φ = 90°, -180° < θ < 180°
Figure 10 presents the Co-Pol E-plane radiation pattern (dB) with fixed φ at 90° and θ swept
from -180° to 180°. Radiation patterns were simulated with DGS implemented.
11
Figure 11: HFSS Circular Ring Patch Antenna Directivity (dB) vs. Frequency (GHz), f = 2.4GHz
Figure 12: HFSS Circular Ring Patch Antenna Directivity Radiation Pattern (dB), f = 2.4GHz, φ = 90°, -180° < θ < 180°
(Above Patch)
12
Figure 13: HFSS Circular Ring Patch Antenna Directivity Radiation Pattern (dB), f = 2.4GHz, φ = 90°, -180° < θ < 180°
(Below Patch)
Figure 11 shows the directivity frequency response (dB), with maximum 5.7dB directivity, within
the typical 5-8dB range for patch directivity. E-plane HPBW is 39°, greater than the expected 36°
E-plane HPBW listed in Table III. Figure 12 and Figure 13 display three dimensional directivity radiation
patterns (dB) above and below the patch, respectively. The color map in Figure 13 indicates the radiation
pattern below the patch has maximum 1.4dB directivity.
13
IV. SYSTEM TESTING AND RESULTS
Figure 14: Circular Ring Patch Antenna (Top View)
Figure 15: Circular Ring Patch Antenna (Bottom View)
Figure 14 and Figure 15 show the fabricated circular ring patch antenna and ground layers. The
HFSS design from Figure 5 is converted to a .dwg layout for fabrication in the Cal Poly graphic
communications electronics screen printing facility. The silver ink circular ring patch is screen printed
onto the top layer. Copper foil adhesive tape covers the bottom-side ground plane.
Figure 16: Test Fixture Mounted Circular Ring Patch Antenna in Anechoic Chamber
14
Figure 17: HFSS Coordinate Axes for Test Fixture Mounted Circular Ring Patch Antenna with Probe Feed
Figure 16 shows patch antenna placement in the anechoic chamber. The antenna is mounted to
the wood and plastic test fixture. Figure 17 shows the test setup orientation in the HFSS coordinate
system. Tests are conducted in the Microwave Laboratory (20-116) anechoic chamber with the Labview
AMS software. The anechoic chamber minimizes reflections with RF (radio frequency) absorbent foam
interior lining. A standard gain horn antenna transmits toward the receiving patch antenna.
Figure 18: Measured Circular Ring Patch Antenna |S11| (dB) vs. Frequency (GHz)
Figure 18 displays return loss characteristics from 1-6GHz. The 20dB return loss bandwidth
includes 2.313-5.550GHz, an 82.335% fractional bandwidth relative to the 3.932GHz center frequency.
15
Table VII: Measured Circular Ring Patch Antenna |S11| (dB) at WLAN Frequencies
Operating Frequency (GHz)
|S11| (dB)
Description
2.313
20.178
Lower 20dB return loss
bandwidth frequency bound
2.400
19.661
WLAN designated frequency
3.700
35.256
WLAN designated frequency
5.000
25.314
WLAN designated frequency
5.550
20.489
Upper 20dB return loss
bandwidth frequency bound
Table VII lists |S11| points of interest.
Figure 19: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB),
f = 2.4GHz, φ = 90°, -180° < θ < 180°
16
Figure 20: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB),
f = 2.7GHz, φ = 90°, -180° < θ < 180°
Figure 21: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB),
f = 3.1GHz, φ = 90°, -180° < θ < 180°
17
Figure 22: Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB),
f = 4.6GHz, φ = 90°, -180° < θ < 180°
Figure 23: HFSS vs. Measured Circular Ring Patch Antenna E-Plane Co-Pol Radiation Pattern (dB),
f = 2.4GHz, φ = 90°, -180° < θ< 180°
18
Figures 19-22 display E-plane co-polarized radiation patterns (dB) at WLAN operating
frequencies. The radiation patterns are directional at the fabricated antenna’s resonant frequencies
2.788GHz, 3.213GHz (maximum observed directivity) and 4.488GHz (maximum observed sidelobe
level). The radiation pattern at 2.4GHz achieves 7.1dB directivity. Figure 23 overlays measured and
simulated radiation patterns at 2.4GHz frequency. Figure 23 indicates the measured radiation pattern has
an approximately 40° HPBW from -70° to -110°.
19
V. CONCLUSION
Table VII lists measured resonant frequencies and corresponding return losses. The fabricated
circular ring patch antenna with ground defect achieved 3.237GHz 20dB return loss bandwidth from
2.313-5.550GHz, an 82.335% fractional bandwidth (see Figure 18). Figures 19-22 confirm directional
radiation patterns at each WLAN operating frequency. The measured radiation pattern achieves 7.1dB
directivity at 2.4GHz. HPBW (E-plane) is approximately 40°.
The measured 20dB return loss bandwidth is 12.033% wider than the target 70.270% fractional
bandwidth covering 2.4/3.7/5GHz. Figure 23 compares simulated and measured radiation patterns at
2.4GHz. The measured antenna’s 7.1dB directivity is 1.4 dB higher than the simulated maximum 5.7dB
directivity. The measured approximate 40° E-plane HPBW is close to the simulated 39° HPBW. The
simulated radiation pattern exhibits a null at 180°, which appears to be absent in the measured radiation
pattern.
The fabricated and simulated antenna’s ground plane differ in terms of ground defect area, shape
and deformation such as corrugations in grounding tape, which could lead to discrepancies. A more
durable probe feed construction could improve the system. Alternative probe feed connections include
embroidery with conductive yarn (less rigid but more durable than solder) and cured conductive epoxy
(more rigid than embroidered connections and solder but as brittle as solder). The circular ring patch
antenna’s operating bandwidth includes unlicensed frequencies from 2.4-5GHz. Notch filters can be
designed to prevent illegal bandwidth access.
20
VI. BIBLIOGRAPHY
1. IEEE Standard for Information Technology, 802.11, 2012.
2. D. M. Pozar and D. H. Schaubert, “Microstrip Antennas: The Analysis and Design of Microstrip
Antennas and Arrays,” Hoboken, NJ: Wiley, 1995.
3. R. Kumar and D. C. Dhubarya, “Design and Analysis of Circular Ring Microstrip Antenna,”
Global J. of Researches in Eng., vol. 11, no. 1, Feb 2011.
4. L. H. Weng, Y. C. Guo, X. W. Shi, and X. Q. Chen, “An Overview on Defected Ground
Structure,” Progress in Electromagnetics Research B. Vol. 7, pp. 173-189, 2008.
5. W. L. Stutzman and G. A. Thiele, “Antenna Theory and Design,” 3rd ed. Hoboken, NJ: Wiley,
2012.
6. B. J. Kwaha, O. N. Inyang, and P. Amalu, “The Circular Microstrip Patch Antenna – Design and
Implementation,” University of Jos and Ajayi Crowther University, Jos and Oyo, Nigeria, 2011.
7. K.C. Gupta, “Broadbanding Techniques for Microstrip Patch Antennas – A Review,” University
of CO Dept. of Elect. and Comput. Eng., Boulder, CO, Rep. 98, 1988.
21
APPENDIX A — PARTS LIST AND COSTS
Table VIII: Circular Ring Patch Antenna Materials and Costs
Module
Cost Estimates ($)
Description
Substrate
0.33
124mm x 124mm x 0.3556mm Mylar®/Polyester Film
Patch
5.98
Silver Metal Ink, Conductive Water-Based Coating, 6g, 5 to 6
µm thickness, 8.54 mm2 coverage area, 33% Ag
Ground
10.34
124mm X 124mm Tapecase Copper Foil Tape
RF Connectors
0.43
1x End Launch PCB Mount SMA Female Plug Straight RF
Connector Adapter
Total
17.08
-
Table VIII lists required materials and costs to produce one unit.
22
APPENDIX B — ANALYSIS OF SENIOR PROJECT DESIGN
1. Summary of Functional Requirements
The fabricated circular ring patch antenna achieves an operating bandwidth that includes
2.4-5GHz WLAN frequencies and 7.1dB directivity at 2.4GHz. The PET substrate is 124mm x 124mm x
0.3556mm (L x W x H). The substrate is thinner than typical microstrip patch antennas (h < 0.003λ).
Antenna size and weight are desirable properties for compact and portable applications. 2.4-5GHz
frequency applications include Wi-Fi Internet, Bluetooth (connecting device and peripherals, device
synchronization), Zigbee (mesh networking, residential and building controls), industrial processes (selfguided vehicles, communication between machines) and public safety (surveillance, emergency
communications).
2. Primary Constraints
Using a lightweight substrate requires design and analysis focused on improving an inherently
more narrow impedance bandwidth. Circular ring microstrip patch design and ground defect
implementation enables a compact antenna to achieve 2.4-5GHz operating bandwidth.
3. Economic
Human capital includes labor costs. Parts manufacturing, retail and delivery require labor.
Substrate production and screen printing processes also require labor. The initial projection based on
material costs for producing one antenna is $17.08 (see Table VIII). The projected costs are difficult to
estimate because the substrate, ground and RF connectors must be purchased in bulk. Commercial HFSS
packages can be accessed in the Microwaves Laboratory (20-116) and cost $50,000. Microwave
Laboratory test assets include the Anritsu MS4622B Vector Network Measurement Systems and all
anechoic chamber equipment including RF absorbent foam, test fixtures, chamber construction materials
and the standard gain horn antenna. The Microwave Laboratory and screen printing facilities require
significant overhead expenses and maintenance. Redesign and fabrication caused weeks of delays during
project development. Since there is no additional research or redesign prior to manufacturing,
approximately one month is required for materials acquisition, fabrication and testing.
4. If Manufactured on a Commercial Basis
23
Table IX: Circular Ring Patch Antenna Single Unit vs. Bulk Materials and Costs
Module
Single Unit Amount
Bulk Amount
Single Unit Cost
Bulk Cost
Estimates ($)
Estimates ($)
Substrate
4.882" x 4.882"
3' x 25'
0.33
148.09
Patch
8.54 mm2
32.77 mm2
5.98
22.95
Ground
4.882" x 4.882"
1” x 18”
10.34
16.08
RF Connectors
1 unit
20 units
0.43
6.03
Total
-
-
17.08
193.15
Table IX compares single unit and bulk materials and costs. Table VIII lists $17.08 total material
costs to produce one unit. Table IX indicates that the product needs to be manufactured and sold in mass
quantities for profit. Expenses for manufacturing one unit are over eleven times greater than single unit
production costs. Materials such as the RF connectors would cost more individually than if bought in
packages containing multiple. Online market research using popular commerce sites (e.g. amazon.com,
newegg.com) indicates that Wi-Fi antennas are regularly priced above $40, and assuming each unit
requires $17.08 in materials expenses, the project can potentially be marketed alongside other consumer
antennas for profit. In order to utilize this product, the user requires a wireless adapter, such as an SMA
to USB adapter. There are no additional operating and maintenance costs for the consumer.
5. Environmental
Substrate PET is manufactured in plastic processing plants. Regulated industrial facilities
establish safe and efficient environments to limit pollution and material consumption. Recycling plastics
is a popular form of environmental conservation in industrial plants. The grounding tape used with the
prototype is composed of copper foil cultivated through copper mining. Naturally occurring conductive
materials such as copper are depleted as the demand for electronics expands and electronics become more
ubiquitous and are manufactured at higher rates. Electromagnetic compatibility standards conformance is
unknown without performing certification tests. Used materials, defective parts and waste should be
recycled or disposed through electronics waste management facilities.
6. Manufacturability
Screen printing with conductive ink prevents the use of many desirable substrates that could meet
24
project specifications, such as textiles. Since the patch antenna is fabricated using precision screen
printing, inaccuracies in attaining the simulated model's dimensional specifications or using conductive
ink deposition and curing are not an issue. Grounding tape deforms easily and corrugations may cause
unwanted effects and involves unnecessary labor and costs to implement, hence, screen printing the
ground plane as an alternative is favorable.
7. Sustainability
Performance errors caused by deformation over long periods of time in portable applications were
not experimentally studied due to the relatively short project time frame. The probe feed coaxial
connection is constructed using rigid yet brittle solder. Alternative feed configurations using embroidered
or cured epoxy connections could potentially enhance the feed connection's durability and extend the
product's lifetime. Implementing design improvements entails another fabrication and testing cycle,
requiring more time, labor and materials and hence more costs. The 124mm x 124mm plastic antenna
consumes relatively little material because of its compact dimensions. Required materials are plastic
(substrate), copper (adhesive tape) and silver (conductive ink).
8. Ethical
The product can potentially be used to access unlicensed bands specified in the IEEE 802.11
protocols. Notch filters that eliminate access to specific frequencies can be configured on the patch to
prevent this issue.
9. Health and Safety
Electromagnetic interference issues including emissions, immunity and signal integrity were not
tested according to standards for regulatory compliance. Noncompliance results in product performance
degradation, adverse effects on other electronics and human exposure to unsafe levels of emissions.
10. Social and Political
Social impacts of the device include wireless congestion due to increased widespread WLAN
access. The 2.4GHz frequency band in particular has become so congested that 5GHz and 5.9GHz are
being used more frequently to allocate bandwidth for 2.4GHz applications. The product impacts wireless
service providers as their services are used more heavily. The antenna's use can lead to signal congestion
in crowded networks, due to RF interference. Interference causes network slowdowns due to the
antenna's inability to distinguish signals and packet loss followed by reconnection attempts. This affects
both the provider's service quality and the user's experience.
25
11. Development
Information available through the IEEE Xplore Digital Library provides insights into patch
antenna theory and design and has proved invaluable to project development. Familiarization with
procedures and test equipment used for antenna measurements such as anechoic chamber measurements
became indispensable knowledge. HFSS design and analysis enriched an understanding of a powerful
tool that is prevalent in the RF industry.
26