1. DESIGNING OF A SMALL WEARABLE CONFORMAL PHASED ARRAY ANTENNA FOR WIRELESS COMMUNICATIONSBy
Sayan Roy
Major Advisor: Dr. Benjamin D. Braaten Dept. of ECE, NDSU, Fargo, ND, USA

2. Contents Introduction Defining the Problem Phased Array Antenna
Realization of Conformal Phased Array Antenna
Designing of Phased Array Antenna Test Platform
Scanning Properties of Phased Array Antenna Test Platform
Four Element SELFLEX Array Design
Scanning Properties of SELFLEX Array
Conclusion

3. Introduction to Array Antenna Conformal Antenna Phased Array Antenna

4. Antenna
For any communication device, an antenna system serves the purpose for external communication wirelessly.

5. Today’s Antenna Systems

6. Array Antenna Array means a collection of similar entities.
Set of individual antenna elements connected together to behave as a single unit
Advantages
Higher Gain
Beam Steering Capability
Reliable
Higher SNR

7. Beam steered 45° from Broadside direction
Beam Steering
In any Antenna system, the transmitting or receiving signal has two attributes:
Amplitude (A) and
Phase (φ).
Beam Steering can be achieved in an array antenna by changing the progressive phase differences between antenna elements.
Beam steered 45° from Broadside direction

8. Beam Steering of a Patch Array Antenna

9. Conformality
Conformality can be described as a map projection which has the property of preserving relative angles over small scales.
In Mathematics, a conformal map is a function which preserves angles.

10. Conformal Antennas
Often mechanical design of a communication system requires that the associated antenna should be mounted on a curved surface.
Applications
Aerospace Designs
Wearable Antenna
Spacesuit
Mobile Devices
For last couple of years, designers have been showing interest in simulating conformal antenna performance to optimize antenna parameters in presence of conformal surface.

11. Defining the Problem

12. Relation between Conformality and Beam Steering
A conformal surface changes its curvature with time and may be planar or non-planar.
When an antenna system lies on a planar conformal surface, the field pattern of the antenna behaves normally.

13. Relation between Conformality and Beam Steering (cont.)
However, when the surface of the antenna becomes non-planar, the performance of the antenna starts to degrade.

14. Relation between Conformality and Beam Steering (cont.)
Beam Steering concept can be implemented to recover the field pattern of the antenna system by proper correction in relative phases between elements of the array.
This type of antenna is known as Phased Array Antenna.

15. Defining the Problem: Can we recover the radiation pattern of a conformal array ?

16. Phased Array Antenna. Defining Co-ordinate. Theory of Array Factor
Phased Array Antenna Defining Co-ordinate Theory of Array Factor Concept of Phase Scanning Phase Compensation Technique of a Conformal Array Antenna

17. Defining Co-ordinate
(θ,φ) is the direction in space

18. Array Factor (AF)
The array factor due to isotropic point sources is the weighted sum of the signals received by the elements.
Mathematically,
where N = number of elements
is the complex weight for element n
k=2π/λ is the wave number
(xn, yn, zn) is the location of element n

19. Array Factor (AF) (cont.)
Unique for each array
Depends on
number of elements,
relative magnitude and phase of current on each element,
relative inter-element spacing and
geometrical orientation of the elements.
Use
Pattern Multiplication Rule
If the response of a single element of a linear array is 𝑬 𝒔
then the total response of the array 𝑬 total can be written as,
𝑬 total = 𝑬 𝒔 𝑨𝑭

20. Concept of Phase Scanning
Phase Scanning Circuitry
Why?
Electronic Beam Steering
Technique
Time Delay Scanning
Frequency Scanning
Phase Scanning
Why Phase Scanning?
Ease of Implementation
Cheaper Digital Control Circuitry
Fast Response Time
High Sensitivity

21. Concept of Phase Scanning (cont.)
How?
By controlling the progressive phase difference between each individual elements of an array.
Implementation
Diode Phase Shifter
Ferrite Phase Shifter
Industrial Solution
Digitally controlled fixed step phase shifter
Analog controlled continuous phase shifter

22. Phase Scanning Technique
Implementation
Series Phasers
Advantage:
Sharing Equal Power
Disadvantages:
Unequal Inter-element Phase Shift,
so complex control circuitry.
Summed up Attenuation
Parallel Phasers
Advantages:
Phase Shifters act independently
Simpler Control Circuit
Disadvantage:
Each phase shifter does not share equal power
Example
Switched Line Phase Shifter
Ferrite Phase Shifter

23. Conformal Antenna- Challenges and Solution
For a conformal antenna, the surface of the substrate changes with time during operation.
When the surface remains planar, the antenna behaves normally.
However for non-planar orientation, the radiation pattern gets distorted.
Solution
By applying the concept of phase steering, correct radiation pattern can be recovered.

24. Realization of Conformal Phased Array Antenna
Realization of Conformal Phased Array Antenna Equation for Phase Correction Proposed System Block

25. Determining possible conformal surfaces in terms of application
Conformal Antennas are used basically as wearable antennas which may be shaped as wedge or cylindrical in non-planar orientation.

26. A linear conformal array antenna placed on a Wedge shaped surface

27. A linear conformal array antenna placed on a Cylindrical surface

28. Equation for Phase Correction
An x- and z- translation is incurred from the original flat position for each array element.
Fields arriving at the reference plane associated with A±2 lagged from fields arriving at the reference plane associated with A±1.
So, the phases of current at A±2 should be positive enough to compensate the phase delay by that free space propagation to maintain equivalent planar orientation.
As the phase has being corrected towards the source, the phase correction will be additive in nature.
For wedge shaped surface, this correction can be achieved by introducing phase 𝚫 𝜱 𝒏 𝒘 to each element where
𝜱 𝒏 𝒘 = +𝒌𝑳|𝒏|𝐬𝐢𝐧 𝜽 𝒃
For cylindrical surface, this correction can be achieved by introducing phase 𝚫 𝜱 𝒏 𝒄 to each element where
𝜱 𝒏 𝒄 =+𝒌𝒓 𝒔𝒊𝒏 𝜱 𝒏 − 𝒔𝒊𝒏 𝜱 𝒏−𝟏

29. Designing of Phased Array Antenna Test Platform

30. Phased Array Antenna Test Platform

31. 4-element antenna array with connectors
g=2.0 mm, h=35.6 mm, t=1.3 mm
w=43.6 mm.
Rogers 6002(εr=2.94) 60 mil substrate.
Resonant Frequency: 2.46 GHz

32. Four port Receiver RF Circuit Board
Consists of
Voltage controlled Analog Phase Shifters
Voltage Controlled Attenuators
Amplifier and
Power Combiner
Industry Available
Each component was tested and verified prior to application with single prototype

33. Control Voltage vs. Normalized Phase of the Phase Shifter

34. Four port Receiver RF Circuit Board (cont.)
Multiple Input Single Output System
RT/duroid mil (εr=2.94)
Controlled by DAC Circuit through LabVIEW GUI

35. DAC Circuit 12 bit, octal, 64 pin, low power DAC
Output ranges from 0V to 33 V for unipolar operation
Allows programmable gain of x4 or x6 w.r.t the applied reference voltage
Features Serial Peripheral Interface that can be operated at 50 MHz and is logic compatible with 1.8V, 3V or 5V
The register consists of a R/W bit, 5 address bits and 12 data bits
Operated in both synchronous and asynchronous mode
TQFP(Thin Quad Flat Package)-64 (10 x 10mm) used

36. LabVIEW GUI
National Instrument LabVIEW USB 6008 peripheral device was used to communicate with the GUI
4 phase shifters and 4 attenuators can be controlled by 8 separate output channels from DAC with precision up to 300 mV

37. Connection Setup of the system

38. Scanning Properties of Phased Array Antenna Test Platform

39. Phase Compensation Calculation
The expression for Array Factor can be redefined in Spherical coordinate as:
where 𝒖= 𝐬𝐢𝐧 𝜽 𝐜𝐨𝐬 𝜱
𝒖 𝒔 = 𝐬𝐢𝐧 𝜽 𝒔 𝐜𝐨𝐬 𝜱 𝒔
𝒗 𝒔 = 𝐬𝐢𝐧 𝜽 𝒔 𝐬𝐢𝐧 𝜱 𝒔
𝒗= 𝐬𝐢𝐧 𝜽 𝐬𝐢𝐧 𝜱
θs is the elevation steering angle
Φs is the elevation steering angle
A is the amplitude to each element
Element factor 𝒆 𝜽 =𝑨 𝐜𝐨𝐬 𝜽
and 𝒘 𝒏 =𝒆(𝜽) 𝒆 𝒋𝜶
Then the compensated Array Factor ( 𝑨𝑭 𝒄 ) will be
𝑨𝑭 𝒄 =𝑨𝑭 𝒆 𝒋 𝜱 𝒏

40. Return Loss Measurement

41. Properties on a flat surface ( 𝜽 𝒃 =0°)

42. Properties on a wedge ( 𝜽 𝒃 =30°)

43. Properties on a wedge ( 𝜽 𝒃 =45°)

44. Properties on a cylinder (r=10cm)

45. Gain Calculation
The primary objective through this correction is to recover the gain.
If the reference gain of the system for a particular orientation is Gr(θ,Φ) and the compensated gain after the correction is Gc(θ,Φ), then for ideal condition
Gr (θ,Φ) = Gc (θ,Φ)
However, the projected spacing between the elements deviates from λ/2 value for any non-planar orientation.
Due to this geometrical limitation, compensated gain can never be achieved to be equal to the reference gain. This gain shift (Gs) has been measured for all conformal cases and compared with analytical result.

46. Gain Calculation (cont.)
Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)
Surface
( 𝜽 𝒃 =30°)
( 𝜽 𝒃 =45°)
Cylinder
Gs, analy.
-0.6 dBi
-1.3 dBi
-0.8 dBi
Gs, meas.
-1.0 dBi
-1.8 dBi
-1.6 dBi
Projected Spacing
0.43λ
0.35λ
non-uniform

47. Test Platform Results Advantages Disadvantages
Practically validates the theory of beam steering
Ability of recovering the radiation pattern has been demonstrated for a general array
Gain Calculation has been presented showing low loss of gain
Disadvantages
Manual control required for any changes of conformal surface
The array was formed by individual element with separate feeding points. But an array should be acting as an individual element.
Gain shift

48. Four Element SELFLEX Array Design

49. SELFLEX Array Design Challenges Solution
Can we design a conformal array on a single substrate with phase correction capability?
Can we achieve radiation pattern recovery for a conformal array in an autonomous manner?
Can we reduce the gain shift?
Solution
By designing a SELFLEX (SELF-adapting FLEXible) array antenna.

50. Proposed System Block Diagram

51. Corporate Feed Network
Why?
Matching.
Technique
Corporate Feed Structure by using quarter-wave transformer
Example
Bifurcated T waveguide or
coaxial T-junctions.

52. SELFLEX Array Design Features: Single feed point
Insertion of phase shifters into corporate feed network
Introduce the sensor circuit as the feedback network with autonomous controller circuitry for radiation pattern recovery

53. Sensor Circuit Setup

54. How it Works
A flexible resistor senses the amount of curvature of the surface each time and feed that value to the controller circuit.
The controller circuit consists of an instrumentation Op-Amp AMP04 that offers the phase shifter with necessary voltage correction for any conformal orientation.
The phase shifters placed on the corporate feed network then process the signals from each array element resulting correction of radiation pattern of the array autonomously.

55. Scanning Properties of SELFLEX Array

56. Return Loss Measurement

57. Properties on a flat surface ( 𝜽 𝒃 =30°)

58. Properties on a flat surface ( 𝜽 𝒃 =45°)

59. Properties on a cylinder (r=10cm)

60. Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)
Gain Calculation
Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)
Surface
( 𝜽 𝒃 =30°)
( 𝜽 𝒃 =45°)
Cylinder
Gs, analy.
-0.6 dBi
-1.3 dBi
-0.8 dBi
(Test Platform)
Gs, meas.
-1.0 dBi
-1.8 dBi
-1.6 dBi
(SELFLEX)
Projected Spacing
0.43λ
0.35λ
non-uniform
-0.9 dBi
-1.4 dBi
-1.2 dBi

61. Conclusion Conformal Phased Array Antenna Theory of Beam Steering
Implementation of RF block
Designing, printing and testing of a primitive conformal array that has the ability to compensate phase on each element with external manual control by the user
Designing, printing and testing of a 1x4 self-adapting antenna that can autonomously preserve its radiation field during conformal application

62. Questions ?
Thank You