THEORY EXAMINATION (SEM–VIII) 2016-17 SATELLITE AND RADAR SYSTEM

Satellite and Radar System – Section Wise Explanation

Section A – Basic Concepts of Satellite and Radar Systems

Section A contains short questions that test the basic concepts of satellite communication and radar technology. Students must attempt all questions in this section. 

Satellite communication is a technology used to transmit signals over long distances using artificial satellites orbiting the Earth. It is widely used for television broadcasting, weather forecasting, navigation systems, and military communication.

One important concept in satellite communication is Direct Broadcast Satellite (DBS) television, which allows television signals to be transmitted directly from satellites to users’ homes through satellite dishes.

Another important concept is noise temperature, which represents the amount of noise present in a communication system. It is important because it affects the quality of signals received from satellites.

To transmit video signals efficiently in DBS systems, video compression techniques are used. These techniques reduce the amount of data required to transmit video signals while maintaining acceptable picture quality.

Satellite systems also use Telemetry, Tracking, and Command (TT&C) systems. These systems help monitor satellite health, track satellite position, and send commands from Earth stations to satellites.

Satellite communication systems operate in different frequency bands, such as:

L-band

Ku-band

Ka-band

These frequency bands are selected based on communication requirements and atmospheric conditions.

Radar (Radio Detection and Ranging) systems are used to detect objects and measure their distance, speed, and direction. Radar systems are commonly used in aviation, weather monitoring, military applications, and traffic control.

An important radar concept is radar resolution, which refers to the ability of a radar system to distinguish between two closely spaced objects.

Another concept is the likelihood ratio test, which is used in radar signal processing to detect targets in the presence of noise.

Understanding these concepts helps engineers design efficient satellite communication and radar systems.

Questions for Section A

What is Direct Broadcast Satellite television?

What is noise temperature and why is it important?

Explain video compression used in DBS systems.

What is Telemetry, Tracking, and Command (TT&C)?

What are the frequency ranges of L, Ku, and Ka bands?

How does radar range equation depend on wavelength?

What is radar resolution?

How is maximum radar operating frequency determined?

What are the applications of radar?

What is the likelihood ratio test?

Section B – Satellite Communication and Radar Signal Processing

Section B focuses on detailed explanations of satellite communication issues and radar system performance factors. Students must attempt any five questions from this section. 

One common problem in satellite communication systems is intermodulation distortion. This occurs when multiple signals pass through nonlinear components such as amplifiers, causing unwanted mixing of frequencies. Engineers use techniques such as power control and linear amplification to reduce this distortion.

Another important phenomenon affecting satellites is the solar eclipse effect. When a satellite passes through the Earth's shadow, its solar panels cannot generate power. During this period, the satellite relies on onboard batteries.

Radar systems also experience system losses, which reduce the strength of received signals. These losses may occur due to antenna inefficiencies, atmospheric absorption, and signal processing limitations.

Another radar concept discussed in this section is beam splitting, which refers to dividing a radar beam into multiple parts to improve detection accuracy and tracking capability.

A delay line canceller is used in radar systems to eliminate unwanted echoes from stationary objects, allowing the radar to detect moving targets more effectively.

Radar echoes from targets depend on the radar cross-section (RCS) of the target. The behavior of radar echoes can be classified into three regions:

Rayleigh region – small target compared to wavelength

Resonance region – target size comparable to wavelength

Optical region – target size much larger than wavelength

Satellite stability in orbit is another important topic. Satellites must maintain proper orientation in space to ensure accurate communication. This can be achieved using methods such as spin stabilization and three-axis stabilization.

Understanding these topics helps engineers improve communication reliability and radar detection performance.

Questions for Section B

Explain intermodulation distortion in satellite links and how it can be reduced.

What is the effect of solar eclipse on geostationary satellites?

Explain different types of system losses in radar systems.

What is beam splitting and how is it implemented?

Explain the working of a delay line canceller.

Describe radar echoes in Rayleigh, resonance, and optical regions.

What factors cause system losses in radar?

What methods are used to stabilize satellites in orbit?

Section C – Advanced Satellite Navigation and Radar Systems

Section C contains advanced questions related to satellite link analysis, GPS technology, and radar system design. Students must attempt any two questions from this section. 

One important topic discussed in this section is the carrier-to-noise ratio (C/N) in satellite communication systems. Engineers calculate C/N ratios for both uplink and downlink channels to determine signal quality.

Another concept is look angles, which are the angles used by an Earth station antenna to point toward a satellite. These angles include azimuth angle and elevation angle.

Engineers calculate look angles based on the Earth station location and satellite position.

Another important technology discussed in this section is the Global Positioning System (GPS). GPS is a satellite-based navigation system that provides accurate location and time information anywhere on Earth.

GPS consists of three segments:

Space segment – satellites orbiting the Earth

Control segment – ground stations monitoring satellite operations

User segment – GPS receivers used by individuals or systems

Another radar technology discussed in this section is the Moving Target Indicator (MTI) radar.

MTI radar is designed to detect moving targets while eliminating reflections from stationary objects such as buildings or terrain.

It works by comparing signals from successive radar pulses and identifying changes caused by moving targets.

Questions for Section C

Derive the expression for the carrier-to-noise ratio (C/N) for uplink and downlink.

What are look angles in satellite communication?

Calculate azimuth and elevation angles for an earth station and satellite.

Explain the position location principle of GPS.

Describe the segments of GPS.

Draw the block diagram and explain the operation of MTI radar.

Conclusion

The Satellite and Radar System exam paper evaluates knowledge at three levels. Section A focuses on basic concepts of satellite communication and radar systems. Section B examines detailed system behavior and signal processing techniques. Section C explores advanced topics such as satellite link analysis, GPS technology, and radar target detection. 

Understanding these concepts is essential for designing modern communication, navigation, and radar systems.