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Satellite to Ground System/Satellite to Satellite System
An EDO Corporation omni directional conical spiral antenna (hyperlink here to ConicalAntenna.pdf, also maybe the company?) was chosen as the satellite’s antenna for space-ground communication as well as satellite-satellite communications. This is possible because of the antenna’s broadband characteristics, and the fact that the other satellites and receivers will be in a single hemisphere. Interference should be minimal since the ground receivers will be operating at 2.10GHz and the satellite receivers will be operating at 2.16GHz. This design will also minimize the number of antennas required to conduct operations. While each link will need its own RF front end, their signals maybe be combined using a combiner before being fed into the antenna.
Antenna Benefits
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Space hardened
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Circularly polarized
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Hemispherical coverage
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Small footprint
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Antenna Specifications
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S-band (1.7-2.3GHz)
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Peak Gain 4dB
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Beamwidth 145 degrees
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Max Power 10W CW
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Satellite to Earth System
Earth will communicate with the satellites via the NASA Deep Space Network (DSN), a collection of satellite dishes around the world that are used for deep space communication. Due to the high data rate and larger distances required for this project, this system will utilize the upgraded 34m antenna array in the Ka band under development at the DSN. Currently, the 70m antennas at each of the facilities in Spain, Australia, and California do not support Ka band transmission. The dishes’ surface roughness is on the order of one centimeter due to its physical large dimensions. Current research is aimed at resolving this issue. However, all of the 34m antennas will be operational for Ka band transmission in the coming years. Four of these antennas can be used in an array to provide the same capabilities as the 70m dish, but at our desired frequency. Satellite uplink will occur at 34GHz while downlink will occur at 32GHz.
NASA DSN 34m Antenna Array (Approximated using values from 70m dish)
- Gain ~87dB at 32-34GHz
- 500MHz Bandwidth
- 20K System Noise
- 400kW Transmit Power
- Circularly Polarized
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Each satellite will be able to transmit to Earth via a Ka band dish antenna modeled after the high gain antenna on NASA’s Voyager spacecraft. Each dish will point to Earth via a mechanically steered control system. Since multiple satellites are in view of the Earth at a given time, the system has redundancy should one of the control systems fail. The network of satellites will decide which satellite will maintain the Earth Satellite link by evaluating which satellite has the highest CNR. This information can then be buffered and distributed to other satellites via the inter-satellite communication network.
Satellite High Gain Antenna
- 3.0m Diameter
- Gain ~60.5dB at 32-34GHz
- 500MHz Bandwidth
- 20W Maximum Transmit Power
- Circularly Polarized
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References
C.A. Balanis, Antenna Theory and Design, Edition 2, New York: John Wiley & Sons, 1997, 466-472, 722-760.
R. Garg, R. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna Design Handbook, Boston: Artech House, 2001, 253-314.
C. Ho and N. Golshan, “Radio Wave Propagation for Communication on and around Mars: Highlights of Parat I: Propagation Through Mars Environment,” Communication Systems and Research Section, Jet Propulsion Laboratory, 1999. [Online]. Available: http://trs-new.jpl.nasa.gov/dspace/handle/2014/17651. [Accessed: October 30, 2008].
United Kingdom Radio Astronomy Network, “Radio Astronomy Frequency Allocations,” National Radio Astronomy Observatory, 2006. [Online]. Available: http://www.ukaranet.org.uk. [Accessed: October 30, 2008]
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