Presentation on theme: "By Sayan Roy Major Advisor: Dr. Benjamin D. Braaten Dept. of ECE, NDSU, Fargo, ND, USA."— Presentation transcript:
By Sayan Roy Major Advisor: Dr. Benjamin D. Braaten Dept. of ECE, NDSU, Fargo, ND, USA
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
Introduction to Array Antenna Conformal Antenna Phased Array Antenna
Antenna For any communication device, an antenna system serves the purpose for external communication wirelessly.
Today’s Antenna Systems
Array Antenna Array means a collection of similar entities. Array Antenna Set of individual antenna elements connected together to behave as a single unit Advantages Higher Gain Beam Steering Capability Reliable Higher SNR
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
Beam Steering of a Patch Array Antenna
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.
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.
Defining the Problem
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.
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.
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.
Defining the Problem: Can we recover the radiation pattern of a conformal array ?
Phased Array Antenna Defining Co-ordinate Theory of Array Factor Concept of Phase Scanning Phase Compensation Technique of a Conformal Array Antenna
Defining Co-ordinate ( θ,φ ) is the direction in space
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 Array Factor (AF) is the complex weight for element n k=2π/λ is the wave number (x n, y n, z n ) is the location of element n
Array Factor (AF) (cont.)
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
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
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
Conformal Antenna- Challenges and Solution Challenges 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.
Realization of Conformal Phased Array Antenna Equation for Phase Correction Proposed System Block
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.
A linear conformal array antenna placed on a Wedge shaped surface
A linear conformal array antenna placed on a Cylindrical surface
Equation for Phase Correction
Designing of Phased Array Antenna Test Platform
Phased Array Antenna Test Platform
4-element antenna array with connectors g=2.0 mm, h=35.6 mm, t=1.3 mm w=43.6 mm. Rogers 6002(ε r =2.94) 60 mil substrate. Resonant Frequency: 2.46 GHz
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
Control Voltage vs. Normalized Phase of the Phase Shifter
Four port Receiver RF Circuit Board (cont.) Multiple Input Single Output System RT/duroid mil (ε r =2.94) Controlled by DAC Circuit through LabVIEW GUI
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
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
Connection Setup of the system
Scanning Properties of Phased Array Antenna Test Platform
Phase Compensation Calculation
Return Loss Measurement
Properties on a cylinder (r=10cm)
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 G r (θ,Φ) and the compensated gain after the correction is G c (θ,Φ), then for ideal condition G r (θ,Φ) = G c (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 (G s ) has been measured for all conformal cases and compared with analytical result.
Gain Calculation (cont.) Surface Cylinder Gs, analy dBi-1.3 dBi-0.8 dBi Gs, meas dBi -1.8 dBi -1.6 dBi Projected Spacing 0.43λ 0.35λ non- uniform G s (θ,Φ) = G c (θ,Φ) - G r (θ,Φ)
Test Platform Results Advantages 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
Four Element SELFLEX Array Design
SELFLEX Array Design Challenges 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.
Proposed System Block Diagram
Corporate Feed Network Feed Network Why? Matching. Technique Corporate Feed Structure by using quarter-wave transformer Example Bifurcated T waveguide or coaxial T-junctions.
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
Sensor Circuit Setup
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.
Scanning Properties of SELFLEX Array
Return Loss Measurement
Properties on a cylinder (r=10cm)
Gain Calculation Surface Cylinder Gs, analy dBi-1.3 dBi-0.8 dBi Gs, meas. (Test Platform) -1.0 dBi -1.8 dBi -1.6 dBi Gs, meas. (SELFLEX) Projected Spacing 0.43λ 0.35λ non- uniform G s (θ,Φ) = G c (θ,Φ) - G r (θ,Φ) -0.9 dBi -1.4 dBi -1.2 dBi
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