LITERATURE SURVEYtransponder -downlink- radio frequencies-femtosatellite- coherent detector-AGC- LNA-antennaPROPOSED WORK WITH METHODOLOGYThe C band covers the frequency range between 4 to 8GHz.The transponders operating at this frequency range are called Cband transponders. The basic transponder locks onto a constant carrier uplink tone and generates a constant carrierdownlink tone which is phase-coherent with the uplink.
aluminum shells present in the transponder maintains rigidity ofthe structure and provides electromagnetic shielding.The power supply unit we use in this proposed transponder is a transformer coupled DC-DC converter and itsupplies regulated voltages to the transponder and its subsystems. The down converter is used to supply the frequencyconversion and the gain required for the functioning of the transponder.
In this ,there are two local oscillators that aremade to get locked to a predetermined reference given by the coherent detector. Variable gain amplifiers present in thedown converter are also a subsystem of the automatic gain control(AGC) function.The coherent detector/reference generator consists of a final frequency translation stage. It converts to a basebandsignal which are meant to control the frequency control loop and the automatic gain control loop(AGC). The controlvoltage of the frequency control loop is used to tune a low-noise voltage controlled crystal oscillator to keep track on theuplink carrier. This reference is used to develop a down converter local oscillator signals and the coherent downlinkcarrier.
Like this uplink and downlink phases are kept in matching “lockstep.”The functionality of this includes carrierdetect circuitry and special switched-bandwidth loop filters.The transmitter has a local oscillator locked to the precision reference signal and a RF power amplifier. Thecontrol unit is a microcontroller programming all the phase-locked loops and sets the default transponder state as power-up. It also performs basic control and telemetry interfacing with the spacecraft control systems. A simple RS-232 serial linkCENTRE FOR TECHNOLOGY DEVELOPMENT AND TRANSFERStudent Innovative Project (2017-18) – Proposal ReportSIP ID – 1617S4063Page 1 of 7is provided for ground testing.
SPECIFICATIONS:Uplink frequency of the proposed transponder : 7.15-7.19GHzDownlink frequency of the proposed transponder : 8.4-8.45GHzTx/Rx ratio of the proposed transponder : 880/749Tx RF power of the proposed transponder : 3WAcquisition power level of the proposed transponder : <-134dBmTracking power level of the proposed transponder : <-134dBm -140dBmTypical IF bandwidth of the proposed transponder : 3.
5kHzPower supply of the proposed transponder : 26-32vNoise figure of the proposed transponder : <3dBIMPLEMENTATIONThe subsystems of the transponder are as follows:1. Power supply unit2. Down converter3. Coherent detector/ reference generator4. Transmitter5. Control unitParameters like antenna gain, transmitter power,receiver sensitivity, provide a reliable path to meet ourobjectives.
CENTRE FOR TECHNOLOGY DEVELOPMENT AND TRANSFERStudent Innovative Project (2017-18) – Proposal ReportSIP ID – 1617S4063Page 1 of 7Antenna positioning and tracking equipments are adjustable to compensate for positional variation in the satellite.Physical structure are designed to withstand the harsh climates. The radome or de-icing equipment makes surethat the transponder functions properly during snow or icing conditions.Outdoor Equipment :An antenna for has a low noise amplifier for reception and a down converter for converting microwave tointermediate frequencies. For transmission, additional equipment is required: an upconverter for converting frequenciesfrom intermediate to microwave frequencies, and a solid state power amplifier for boosting signals for transmission.
Antenna Configuration:Low Noise Blockconverter:Since the transmitted signal travels a vry long distance ,it is very weak at the time of reception, it is amplified to a rangethat can be used for communication. A low noise amplifier achieves this without burying the transmitted signal withinternal amplifier noise. Most ground stations today utilize solid state low-noise amplifiers comprising field effecttransistors (FETs) made of from gallium arsenide (GaAs),a semiconductor material. This device is less noisy ,extremelyrugged and reliaWORK PLANTo design the mixer ,amplifier,filters present in the downconverter and the coherent detector/reference generator,transmitter section of the transponderEXPECTED OUTCOME / RESULTSThe femto satellite with proposed transponder is expected to function as a better communication satellite withefficient size and cost.APPLICATIONSC-band transponders are widely used for the telemetry, telecomm and control of satellite. This requires fullprotection from all other external interferences –such as risk of losing control.C-band is used to enhance the air traffic control systems in areas where land coverage is unreliable. TheCENTRE FOR TECHNOLOGY DEVELOPMENT AND TRANSFERStudent Innovative Project (2017-18) – Proposal ReportSIP ID – 1617S4063Page 1 of 7interconnection between the remote VHF towers and the air traffic control centre is given by C-band FSS systems.
C-bandcan supply the required reliability for safety services.It is not preferred to be replaced using other bands .it withstands all climatic conditions imposed on it. It providesSufficiently high reliability in tropical and high-rain regions.CONCLUSIONThus with all these above furnished details and the gained knowledge ,we will be able to design an efficient C bandtransponder to be used in