2.45 GHz Right-Hand Circular Polarized Helical Antenna

Project Overview

A few of the Cube Satellites (CubeSats) that the JHU CubeSat Team desires to communicate with have specific polarization directions and frequencies. One CubeSat in particular has a 2.45 GHz right-hand polarized signal, which means that this ground station requires a similar antenna that can receive such polarized frequencies. I was tasked with designing, manufacturing and assembling this antenna. Special thanks to Steve Hope and Aidan Gray at the Instrument Development Group (IDG) at JHU for this project and for their guidance/instruction to help me learn about something I've become passionate about! This project was definitely a team effort and could not have gotten done so efficiently (~4 weeks!) without all hands on deck.

Design Highlights

Helical Antenna MATLAB Calculator

I built a MATLAB application to help calculate the proper dimensions for the antenna, along with where along the support towers the helix will intersect for ease of hole placement

RHCP Antenna - CAD Assembly

Above, the SolidWorks CAD assembly can be seen of the antenna. Parts have been colored for ease of visibility.

The three towers are spaced 120 degrees apart to support the copper wire helix. Additionally, there are circular supports that have slots to stiffen the towers.

Mounted Antenna

Using laser cutters, the towers and supports were made from acrylic. Acrylic was chosen due to its dielectric properties as to reduce the interference of the electromagnetic field of the antenna. Additionally, it has high UV resistance, meaning it is a good choice for when the full ground station is mounted on the roof of Bloomberg Center for Physics and Astronomy.

Full Ground Station Antenna Boom

The RHCP antenna can be seen mounted with the other two antennas that will be used by the JHU CubeSat Team. It will be oriented using using the central rotator (orange/blue motors).

Requirements

The antenna shall be designed to properly operate at 2.45 GHz frequency
The antenna shall be designed with the following parameters:
- The helix/coil shall have 18 turns
- The coil shall be made using 2.7 mm diameter copper wire
The antenna shall be mounted to a reflector, dimensions of which shall be determined using the proper helical antenna calculations
The full antenna shall be mountable to the existing boom
The material of the antenna shall minimize interference with the performance (frequency, gain, electromagnetic wave)
The antenna shall be able to withstand outside conditions, including rain, snow, and wind

Additional Photographs and Information

Below, the design iteration and progression can be seen. Often, changes would be made after receiving feedback from various professors and instructors that would be the users of the system. Other changes were made when something in the system failed. Descriptions of each of the designs and changes can be found below.

The Matching Section
(Quarter Wavelength a.k.a. λ/4)

Helical antennas have an additional stretch of "wire" at the bottom known as the matching section or quarter-wavelength standoff. The purpose of this λ/4 standoff is to transform the impedance of the main helix to the coaxial cable (which transmits the signal). This section can be seen on the left.

The actual λ/4-wavelength conductor is within this part, and was sealed within. The goal was to make this part waterproof due to its use outside. This was done using adhesive lined heat shrink. Courtesy to Steve Hope and Aidan Gray of the Instrumentation Development Group (IDG) at JHU for their design of this part and teaching me about its purpose.

The antenna tower design was made with Steve and Aidan's design in mind, and aligned the copper helix properly so that it could be soldered to the standoff with minimal additional wire.

There is a threated part on the bottom that allows for the coaxial cable to attach to the antenna.

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