modeling printed antennas using the matlab antenna toolbox wajih iqbal clemson university advisor:...
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Modeling Printed Antennas Using The Matlab Antenna Toolbox
Wajih IqbalClemson UniversityAdvisor: Dr. Martin
Outline
Background Integral equations and method of
moments overview Formulating the antenna model LP patch antenna Future work
Background
Graduate students usually use Ansoft HFSS for antenna modeling
Too complicated and expensive for undergrads
A much easier and user-friendly code has been developed by Makarov (Worcester Polytechnic Institute) called the Matlab Antenna Toolbox (MAT)
Background (cont’d)
The code is based on method of moments and is limited to about 7000 unknowns
The code is reasonably precise for simple printed antennas
I have modeled and studied 15 different antenna structures
Integral Equations and Method of Moments Overview
Statement of an Electromagnetic Boundary Condition
Consider an incident wave (with no z variation i.e. 2D problem)
5
E Exs
xi 0 on strip
Perfectly conductingthin strip
- w
ix
w
y
Ei
90 - i
i
Formulation of an Integral Equation
E xk
d
dxk J x H k x x dxx
s
w
wbg bg c hbg FHG
IKJ
z4
2
22
02
E Exs
xi 0 on strip
E E exi i i jk x i
0 sincos e j
,s ix xE E x w w
The Electric Field Integral Equation
4
20
2
kk J x H k x x dx
w
w
RST zbg c hbg
UVW
zd
dx
d
dxJ x H k x x dx E x x w w
w
w
xibg c h bg b gbg
02 ,
The current on the strip is the unknown to be determined. The unknownquantity is under the integral sign.
J w J w b g bg0
Solution of Integral Equations (MoM)
Step 1: Approximate unknown (surface current) by means of a finite sum of N known functions each with an unknown coefficient.
1
( )N
n nn
I
J r f r
Three Major Steps
UVW
zd
dx
d
dxJ x H k x x dx E x x w w
w
w
xibg c h bg b gbg
02 ,
Solution of Integral Equations (MoM)
Step 2: Substitute the approximation (Step 1) into the IE and establish a well-conditioned system of linear equations by enforcing the resulting equations over N subintervals which are within the interval where a solution is desired
1
( )N
n nn
I
J r f r
4
20
2
kk J x H k x x dx
w
w
RST zbg c hbg
(substitute and apply testing function)
1 11 2 12 3 13 4 14 1
1 21 2 22 3 23 4 24 2
1 31 2 32 3 33 4 34 3
1 41 2 42 3 43 4 44 4
for subinterval 1
for subinterval 2
for subinterval 3
for subinterval 4
i
i
i
i
J Z J Z J Z J Z E
J Z J Z J Z J Z E
J Z J Z J Z J Z E
J Z J Z J Z J Z E
J Z E m Nn mn mi
n
N
, , , ,1 2
1
Solution of Integral Equations (MoM)
Step 3: Solve the N by N linear system of equations from step 2 and thereby obtain values for the coefficients.
11 12 13 14 1 1
21 22 23 24 2 2
31 32 33 44 3 3
41 42 43 44 4 4
i
i
i
i
Z Z Z Z J E
Z Z Z Z J E
Z Z Z Z J E
Z Z Z Z J E
Z J Emn n mi
1
11 12 13 141 1
21 22 23 242 2
31 32 33 443 3
41 42 43 444 4
i
i
i
i
Z Z Z ZJ E
Z Z Z ZJ E
Z Z Z ZJ E
Z Z Z ZJ E
1 in mn mJ Z E
Once we have found J(r) we can find all the radiation properties of the antenna
Why Printed Antennas?
Printed antennas are low-profile planar structures that utilize printed circuit board (PCB) technology
They are compact, low cost, easy to manufacture and suitable for integration with electronic systems
Multi-band operation can also be achieved by integrating several coupled printed antenna elements of different lengths and geometries on the same PCB
Dimension can be smaller with higher dielectric GPS, Radar, Satellite communication, Military, cell
phones, and wireless laptops
Execution Flow Chart
Create 2D geometry
Create 3D geometry and feed
Patch Ground Plane
Feeding Probe
MoM Calculations
4
20
2
kk J x H k x x dx
w
w
RST zbg c hbg
UVW
zd
dx
d
dxJ x H k x x dx E x x w w
w
w
xibg c h bg b gbg
02 ,
J Z E m Nn mn mi
n
N
, , , ,1 2
1
1
( )N
n nn
I
J r f r
Z J Emn n mi
Input impedance/Return loss
Near field and far field properties
-0.02-0.01
00.01
0.02
-0.03
-0.02
-0.01
0
0.01
0.02
0.0300.511.5
x 10-3
xy
z
Patch Ground Plane
Feeding Probe
Formulating the Antenna Model
Design:
Dielectric
View with Dielectric
View without Dielectric
•Linearly polarized patch antenna •Patch is 30x40mm •Ground plane is 50x60mm•Substrate has εr = 2.55
Side View
Patch
Ground Plane
Feeding Probe
2-D Mesh Projection
Feed point
Patch
Ground plane
Volume Mesh Generation
Layer(s) properties
Substrate structure
Ground plane
Vertical metal faces
Feeding points
Patch
3D model ready!
Properties of the Patch Antenna
4800 unknowns took 1.5 hours for 50 frequency points (65sec for each point)
Input Impedance
Solid line – Matlab
Dotted line – Ansoft HFSS
Resonance
Properties of the Patch Antenna
Return Loss
2.93 GHz 2.99 GHz
2.96 GHz
2.99 2.932%
2.96Bandwidth
Far Field Properties
Directivity (xz-plane)
Co-polar dominates
At 2.96GHz
Front to back ratio is about 10dB
Far Field Properties
Total Directivity (dB) 3D Directivity
The maximum directivity is approximately 7.4 dB at zenith
Near Field Properties
z-Directed Electric Fieldx-Directed Electric Field
xy
y-Directed Electric Field
Near Field Properties
Surface Current Distribution (x-directed)Surface Current Distribution (y-directed)Surface Current Distribution (z-directed)
Future Work
Simulate more multiband antennas accordingly with future wireless communication needs
Incorporate the genetic algorithm with the code for antenna optimization
After convergence studies construct and test a multiband antenna in the spherical near field chamber
Acknowledgements
Dr. Anthony Martin
Dr. Daniel Noneaker
Dr. Xiao-Bang Xu
Michael Frye
Questions
? ? ? ? ? ? ? ?