CS6271 - Evolutionary Computation [Week 4]

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• [ ] Watch backlog lecture content.
• [ ] Watch and understand this week's content.
• [x] Complete exercise set 2 and submit assignment.
• [x] Read week 4's research paper.
• [x] Submit quiz on week 4's paper.
• [x] Participate in GD.

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Notes on this week's research paper:

Main goal

• Present an evolved X-band antenna design and flight prototype for NASA's (Space Technology 5) ST5 mission.
• This mission aims to demonstrate and validate new and cutting edge technologies that can be used for future space missions.

How are EAs used here?

• The authors use two Evolutionary Algorithms (EAs) to search the design space and automatically find effective solutions that would ordinarily be very difficult if not impossible for human designers to discover. The two EAs used here are:
  • Genetic Algorithm (GA) that did not allow for branching in the antenna arms.
  • Each individual was represented as a fixed-length binary string that encoded the values of the antenna parameters, such as the length and radius of each arm.
  • The binary string was decoded into a real-valued vector using a linear mapping.
  • The fitness function was designed to maximize the gain of the antenna while satisfying the mission requirements and constraints.
  • Genetic Programming (GP) style tree-structured representation that allowed for branching of antenna arms.
  • Each individual was represented as a tree of nodes that encoded the values of the antenna parameters.
  • The tree structure allowed for branching in the antenna arms, which increased the design space and flexibility.
  • The fitness function was designed to maximize the gain of the antenna while minimizing its complexity and satisfying the mission requirements and constraints.

Advantages of the evolved antennas:

• It has potential power savings, as it achieves high gain across a wider range of elevation angles.
• It has a simpler design and fabrication, as it does not require a matching network nor phasing circuit.
• It has more uniform coverage, as it has a uniform pattern with small ripples in the elevations of greatest interest.
• It has a shorter design cycle, as it took less time and effort to produce than the quadrifilar helical antenna which was a human designed solution.
  • Quadrifilar Helical Antenna: A quadrifilar helical antenna is a type of helical antenna that consists of four wires wound in the form of a helix. The wires are arranged in a way that allows the antenna to transmit and receive circularly polarized electromagnetic waves. Quadrifilar helical antennas are commonly used in satellite communication, GPS navigation, and radiofrequency detection because they are highly resistant to interference. They can be produced by printing to reduce costs and the antenna size can be controlled by using dielectric substrates for the antenna core.

Mission constraints for ST5:

• The gain pattern of the antenna must be greater than or equal to 0 dBic at 40° < θ < 80° and 0° < φ < 360° for right-hand circular polarization.
• The antenna must have a voltage standing wave ratio (VSWR) of under 1.2 at the transmit frequency (8470 MHz) and under 1.5 at the receive frequency (7209.125 MHz).
• The input impedance should be 50 Ω at both frequencies.
• The antenna is restricted in shape to a mass of under 165 g, and must fit in a cylinder of height and diameter of 15.24 cm.
• An additional “desired” specification was issued for the field pattern, which required high gain in the field pattern at low elevation angles.

Additional pointers and context for reference:

The antenna design problem requires two features that are hard to achieve simultaneously:

1. Wide beamwidth for a circularly-polarized wave:
   • This means that the antenna should be able to transmit and receive electromagnetic waves that have a circular shape and a constant orientation in any direction within a large angle range.
   • This is important for communication with the ground station regardless of the spacecraft’s orientation.
2. Wide bandwidth:
   • This means that the antenna should be able to operate at different frequencies without losing much power or signal quality.
   • This is important for data transmission and reception at different rates and modes.

These two features are challenging to design because they often conflict with each other. For example, increasing the beamwidth usually reduces the gain (the strength of the signal) and increasing the bandwidth usually increases the VSWR (the ratio of reflected to transmitted power). Therefore, finding an optimal balance between them requires a sophisticated design method.

X-band:

X-band refers to a frequency range of electromagnetic waves that is commonly used in satellite communication and radar systems. The X-band frequency range is approximately 8 to 12 gigahertz (GHz), which corresponds to a wavelength of approximately 2.5 to 3.75 centimeters. The ST5 mission required an X-band antenna that could transmit and receive circularly polarized waves with a wide beamwidth and bandwidth, which was a challenging design problem.

Week 05 Discussion Group.pdf

[sprince0031]

Week 4 submissions done. However, need to catch up on backlog lecture content. Carrying over this to the current open issue.