Illinois Tiny Satellite Initiative

University of Illinois @ Urbana-Champaign
ITSI UIUC
 Satellite Antenna

Satellite Antenna

The satellite antenna is a critical part of the communication system. Without the antenna, communication between the satellite and the ground station would not be possible. There are several key components that make up the antenna system: antenna element, power divider/combiner, and RF circuit board.

The ION will communicate with the ground station through a dipole antenna. The dipole antenna's radiating element is composed of cross-curved steel strips, typically used in tape measure. Two antenna elements of a quarter-wave will realize the half-wave dipole. The antenna elements will have a 180 phase separation from each other and exhibit linear polarization.  

During the launch of the satellite, the antenna elements will be tied down along the sides of the satellite.  After the initial release of the satellite into it's orbit, the computer will switch on current to a loop of metal wire surrounding some nylon wire, melting through it. The natural tension in the tape-measure stock will cause it to flip up into the ready position. This only needs to be done once, and is irreversible.

A power divider/combiner will be used to balance the power to and from the input and output ports. It will also shift one of the output ports by 180, which combines with the other output port to get a single mixed signal connecting to the radio.  

A microstrip antenna design is used for signal distribution as a RF waveguide to the antenna elements or to the radio. It also provides a structural support for mounting critical components for antenna operation as well as provides a parallel surface for mounting the steel strips of the antenna elements. The backplane side of the antenna board will be completely copper clad. The other side will contain line traces of a designed line width, which will connect the antenna components.

 Ground Station Antenna

A Circularly Polarized Yagi Antenna is located on the roof of Everitt Lab on the University of Illinois' campus.  With other equipment to compensate for Doppler shift and amplification, we are able to communicate with the CubeSat satellite in a 650km (~400m) orbit as it passes over our ground station.  The satellite ground tracks allows for two ten-minute periods of communication, one period at 10:00am and another at 10:00pm.

A ground station has been set up within Everett Labs to handle communication with the satellite. The station consists of a computer to control the rotor that points the antennas on the roof at the satellite which is being tracked, the antennas (70 cm band), the control for the rotor, and an amateur band HAM radio. A modem can be connected to the radio in order to transfer data to and from the satellite.

In order for the station to maintain communication with the satellite, the antenna must be pointing in the correct direction. The rotor on the roof points the antenna to the azimuth and elevation coordinates given by the controller inside the building. A serial connection between the computer and the device which controls the rotor allows communication and control via the computer.

Software named "SatTrack" has also been placed onto the computer which takes information on known satellites, outputting coordinates to a file for use in tracking. There is also information that will be useful in the calculation of Doppler Shift when we are sending and receiving information which is provided by SatTrack. Another program is used to interpret the output of SatTrack and point the antennas according to that information.

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