Chapter 7. The Space Segment 第七章 空間段 亞洲大學 資訊工程學系碩士班 呂克明教授 二○○六年十一月十三日 9/22/2019

Chapter 7. The Space Segment (第七章空間段) Introduction (緒言) The Power Supply (動力供電電源) Transponders (轉發器) Homework Problems (習題) 9/22/2019

Introduction (緒言) The space segment (空間段) includes the satellite and ground facilities needed to keep the satellite operational such as tracking, telemetry, and command (追蹤, 遙測, 與控制, TT&C) facilities. Payload (負載): The equipment used to provide the service for which the satellite has been launched. Two (2) main sections of payload: Transponder and antennas (轉發器與天線) Transponder (轉發器): The equipment which provides the connecting link between the satellite’s transmit and receive antennas. (衛星發射與接受天線) Transponder forms one of the main sections of the payload, the other being the antenna subsystems. 9/22/2019

The Power Supply (動力供電電源) The primary electrical power for operating the electronic equipment is obtained from solar cells (太陽能電池組). The arrays of cells in series-parallel connection (太陽能電池組是串聯與並聯連接而成的) are required. The solar panels of H376 satellite produce 940 W DC at BOF (初期) and 760 W at EOF (末期,約10 yrs). Two (2) Ni-Cd batteries of H376 deliver 830 W during eclipse and recharge time is less than 16 h at EOF. Solar sails (太陽能帆板): Solar panels of H601 are arranged in the form of rectangular solar sails and stretch to 316.5 cm when fully extended. In comparing to the power capacity of cylindrical and solar-cell satellites, the crossover point is estimated to be about 2 kW, where the solar-sail type is more economical than the cylindrical type. 9/22/2019

Transponders (轉發器) A transponder is the series of interconnected units which forms a single communications channel between the receive and transmit antennas in a communication satellite (轉發器是一連串的互聯單元.它們形成通訊衛星內收發天線的單一通訊頻道). The bandwidth allocated for C-band service is 500 MHz and divided into 12 sub-bands (C-波段衛星的頻寬是500兆赫. 可分成12個子頻道). Each transponder has one sub-band and the bandwidth of each sub-band is 36 MHz with 4 MHz guard-band (每一個轉發器有一個36兆赫和同時具有4兆赫保護帶的子頻道). 9/22/2019

Transponders (轉發器)(continued) By making use of polarization isolation, the number can be doubled (使用極化隔離, 這個數目可以加倍). Polarization isolation refers to the fact that carriers, which may be on the same frequency but with opposite senses of polarization, can be isolated from one another by receiving antennas matched by the incoming polarization (極化隔離的意思是相同頻率但是不同極化的載波, 在收發波束主瓣能量上有所區隔). The bandwidth allocated for Ku-band service is 500 MHz and divided into 8 sub-bands (Ku-波段衛星的頻寬是500兆赫. 可分成8個子頻道). Each transponder has one sub-band and the bandwidth of each sub-band is 54 MHz with 7 MHz guard-band (每一個轉發器有一個54兆赫和同時具有7兆赫保護帶的子頻道). 9/22/2019

Transponders (轉發器)(continued) Transponder consists of wideband receiver (寬頻接收器), input de-multiplexer (解調器), and power amplifier (功率放大器). Wideband receiver (寬頻接收器)- The first stage in the receiver is a low-noise amplifier (LNA). The overall noise temperature must take into account the noise added from the antenna. The input de-multiplexer separates the broadband input, covering the frequency range 3.7 to 4.2 GHz (C-band) or 11.75 to 12.25 GHz (Ku-band) into the transponder frequency channels. Redundant receiver (備援接收器): A duplicate wideband receiver is provided so that if one fails, the other is automatically switched in. 9/22/2019

Transponders (轉發器)(continued) The receiver includes a low-noise amplifier (LNA) and a mixer. LNA – The amplifier adds little noise to the carrier being amplified, and at the same time it provides sufficient amplification for the carrier to override the higher noise level present in the following stage. System noise – The major source of electrical noise in equipment is that which arises from the random thermal motion of electrons in various resistive and active devices in the receiver. Antenna noise - Thermal noise is also generated in the lossy components of antennas, and thermal-like noise is picked up by the antennas as radiations. Amplifier output noise energy: N = k * (T ant+ Te), p.315 Te is amplifier noise temperature, K T ant is antenna noise temperature, K k = 1.38 x 10 ** -23 J/K, Boltzmann’s constant (p.312) Mixer – It provides a local oscillator signal for the frequency-conversion process. They provide the frequency conversion for the C-band 6/4-GHz and the Ku-Band 14/12-GHz transponders. 9/22/2019

Transponders (轉發器)( continued) The input de-multiplexer separates the broadband input, covering the downlink frequency range 3.7 to 4.2 GHz for C-Band. What’s the downlink frequency range for the Ku-band? 12.2-12.7 GHz. Traveling-wave tube amplifiers (TWTA, 行波管功率放大器) are widely used in transponders to provide the final output power required to the transmit antenna. 9/22/2019

Homework Problems (習題) 7.12 Draw to scale the uplink and downlink channeling schemes for a 500 MHz bandwidth C-band satellite. Assume the use of 4 MHz guard-bands. 7.13 Explain what is meant by frequency reuse, and describe briefly two methods by which this can be achieved. 7.14 Explain what is meant by redundant receiver in connection with communication satellites. 7.23 Please search ROCSAT 1 and 2 from web. Summarize their history, specifications, and current status. 7.24 Please define the TT&C and describe how the ground facility command the satellite in space. 9/22/2019