Test: RADAR (Radio Detection & Ranging) - Electronics and Communication Engineering (ECE) MCQ

MTI Radar:

MTI radar operates on low pulse repetition frequencies thus causing ambiguous Doppler measurements (blind speeds) but unambiguous range measurements (no second-time-around echoes).

Pulse Doppler Radar:

Pulse Doppler radar operates on high pulse repetition frequency thus causing unambiguous doppler measurements (no blind speeds) but ambiguous range measurements (second-time-around echoes).

PRF:

The pulse repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit, normally measured in pulses per second.

In radar, a radio signal of a carrier frequency is turned on and off; the term "frequency" refers to the carrier, while the PRF refers to the number of switches.

Both are measured in terms of cycle per second, or hertz.

TWT (Travelling Wave Tube) is an electron tube used for amplification at microwave frequencies- generally identified as frequencies between 500 MHz and 300 Hz.. 
Its power generation capability range from watts to megawatts.
For helix TWTs, bandwidths may be as high as two octaves or more and power levels of tens to hundreds of watts.
The duty or cycle time of the TWT is the time the TWT is ON divided by the time base. TWT has the advantage of producing a high duty cycle.

The magnetron is a vacuum tube that is used to generate microwaves of high power.

• Its working principle is based on the interaction between electron stream and magnetic field.
• It works on direct current power.

The range of the radar is given as:

G = Antenna Gain

σ = Radar Cross-Section

Pr = Reflected Power

Ae = Effective Area of the Antenna

Observation:

We observe that, R ∝ (P_t)^1/4

Now, to double the range R, Pt has to be increased by a factor of 16

The radar principle is used in the detection of aircraft.

Radar:

• Radar is an acronym for Radio Detection and Ranging. 
• The term "radio" refers to the use of electromagnetic waves with wavelengths in the so-called radio wave portion of the spectrum, which covers a wide range from 104 km to 1 cm.  
• It is basically an electromagnetic system used to detect the location and distance of an object from the point where the RADAR is placed.
• It works by radiating energy into space and monitoring the echo or reflected signal from the objects.
• It works on radio frequency in the range of about 3 kHz to 300 GHz.
• But most of the RADAR operates between 220 MHz to 35 GHz.

Radar systems have been used in military applications for

• Ground surveillance 
• Missile control, fire control,
• Air traffic control (ATC),
• Moving target indication (MTI),
• Weapons location
• Vehicle search

• In monopulse antenna the simultaneously two or more lobes of antenna are used to track a target hence give better tracking than other methods.
• Monopulse radar is a radar system that uses additional encoding of the radio signal to provide accurate directional information.
• The name refers to its ability to extract range and direction from a single signal pulse.
• Monopulse radar avoids problems seen in conical scanning radar systems, which can be confused by rapid changes in signal strength.
• This system also makes jamming more difficult.
• Most radars designed since the 1960s are monopulse systems.
• The monopulse method is also used in passive systems, such as electronic support measures and radio astronomy.
• Monopulse radar systems can be constructed with reflector antennas, lens antennas or array antennas.
• Historically, monopulse systems have been classified as either phase-comparison monopulse or amplitude monopulse. This is because some common implementions have been based on a phase comparison or an amplitude comparison.
• Modern systems determine the direction from the monopulse ratio, which contain both amplitude and phase information.
• The monopulse method does not require that the measured signals are pulsed. 

The range of the radar is given as:

G = Antenna Gain

σ = Radar Cross-Section

P_r = Reflected Power

A_e = Effective Area of the Antenna

∴ R_max ∝ (P_t)^1/4

To double R_max, P_t must be increased by a factor of 16

MTI refers to Moving Target Indication. It may be considered as a mode in which radar systems are operated so as to discriminate the target against any form of clutter.

Rayleigh scattering is the effect that creates Earth’s blue sky and red sunsets. It is named after the British physicist Lord Rayleigh.

LIDAR is a system similar to radar. It is a system that predominantly uses infrared light from lasers rather than radio waves. It makes use of the other parts of the electromagnetic spectrum.