Ka-band satellite beacon transmitters
- Paper number
IAC-08.B2.4.6
- Author
Mr. SRIMOHAN SRIVASTAVA, INDIAN SPACE RESEARCH ORGANIZATION AHMEDABAD, India
- Coauthor
Mr. ALAK BANIK, Indian Space Research Organization (ISRO),SAC, India
- Coauthor
Mr. JAYESH THAKKAR, Indian Space Research Organisation (ISRO), SAC, India
- Coauthor
Mr. KIRAN GUJARATHI, Indian Space Research Organization (ISRO),SAC, India
- Coauthor
Mr. VINESH GARG, Indian Space Research Organisation (ISRO), SAC, India
- Year
2008
- Abstract
Abstract
Purpose: An increasing number of applications are being planned for Ka-band satellite communication systems mainly due to the demand for higher data rates and high bandwidth in conjunction with the overcrowding of KuC band systems. Ka-band systems typically employ Very Small Aperture Terminals (VSAT’s). While use of smaller earth terminals is attractive from consumer point of view it places a limit on the link margins available. In such application it becomes much important to predict the atmospheric effects to calculate the availability and reliability of the system. GSAT-4 Ka-band satellite will carry two Ka-band beacon transmitters (20.2GHz and 30.5GHz) to support propagation experiments as this band is being introduced first time on a domestic Indian spacecraft. These beacons will be dual-polarized with a switching capability to allow depolarization studies to be performed in addition to conventional propagation experiments. The design and development of 20.2GHz30.5GHz beacon transmitters for Ka-band payload transponder is described in this paper.
Methodology: The transmitter consists of a beacon source, SSPA, switch and a dual-mode horn. The Beacon source provides highly stable beacon frequency signal with good spectral purity, which is amplified by the SSPA. Circular India coverage footprints with a high-gain and high order of polarization purity are provided using frequency-reuse OMT’s and dual-mode horn antennas. This paper covers the critical design parameters of Ka-band beacon transmitter for space use.
Individual sub-system details are given below; • Beacon source generates the required output frequency by successive multiplication of a basic reference TCXO. Here the multiplication order is 200 times for 20.2GHz source (TCXO frequency is 100MHz) and 256 times for 30.5GHz source (TCXO frequency is 119.140625MHz.) The TCXO output is amplified, multiplied and filtered in successive stages to achieve the final output frequency. • The Solid State Power Amplifier (SSPA) consists of low and medium power stages. This subassembly is constructed using hybrid, thin-film, chip-and-wire technology contained in a hermetic housing. • Ka-Band Harmonic Rejection filters are corrugated waveguide low pass filters providing rejection in the second and third harmonic frequencies. • The dual-mode horn is a smooth-walled type providing better cross-polar performance over a conical horn. The horn length and aperture diameter are selected in accordance with the required gain and beamwidth characteristics. A mode generator is used prior to the flare section.
Results: Since the transmitters are to be flown as a part of satellite payload all the sub-systems have been subjected to an environmental test sequence before being delivered for panel level assembly, so as to verify that all the systems are acceptable for flight and can operate in space environment. The sub-systems are meeting the required specifications and the transmitter has an EIRP of 24dBW at 20GHz and 22dBW at 30GHz. The flight model of both the beacon transmitters is ready to be flown in GSAT-4 satellite in second quarter of 2008.
Conclusion: The beacon transmitters have been designed and developed and have successfully cleared the stringent environmental tests. The assembly of beacon transmitters on satellite panel is also completed. The transmitters are part of a Ka-band geo-stationary GSAT-4 satellite which is scheduled to be launched in second quarter of 2008.
- Abstract document
- Manuscript document
IAC-08.B2.4.6.pdf (🔒 authorized access only).
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