AMIETE – ET (NEW SCHEME) - Code: AE78

Subject: RADAR AND NAVIGATIONAL AIDS

Time: 3 Hours Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q.1 must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions, answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or the best alternative in the following: (210)

a. Matched filter used in radar is ________.

. (A) a non-linear network, maximizes signal to noise ratio, when noise spectral density is non-uniform.

(B) linear network that maximizes the out put peak signal to noise (mean) ratio, when input noise spectral density is uniform.

(C) a non-linear network that optimises SNR when noise spectral density is uniform.

(D) an auto-correlation receive that optimises SNR at the RF stage and the mixer stage for optimising the SNR.

b. Method of enhancing cross-range resolution that takes advantage of differential Doppler shift from object at different positions within the antennas angular resolution cell is ________.

(A) SAR

(B) Doppler Beam-Sharpening (DBS)

(C) Inverse Doppler Beam-Sharpening (IDBS)

(D) ISAR

c. Loss caused by not tracking at the peak of the antenna gain _________.

(A) Cross-over loss (B) Polarization loss

(C) Squint loss (D) Integration loss

d. Airport surface detection equipment has the specialized surface search task of keeping track of aircraft on the ground at airports, the PRF class used here is _____.

(A) High PRF (B) Medium or low PRF

(C) Medium PRF (D) Low PRF

e. The equation that specifies the form of the detector law that maximizes the likelihood ratio for a fixed probability of false alarm is ______.

(A) (B)

(C) (D)

f. A radar that increases its PRF high enough to avoid the problems of blind speed      is called _________.

(A) Air surveillance radar (B) Pulse Doppler radar

(C) MTI radar (D) High PRF tracking radar

g. The deflection of the beam or the appearance of an intensity-modulated spot of a radar display caused by the presence of a target is referred to as

(A) Blip (B) Glint

(C) Scintillation (D) Amplitude fluctuation

h. ________ can be a serious limitation in MTI radar since they cause some desired moving target to be cancelled along with the undesired clutter at____ frequency.

(A) Blind speeds, 90 Hz (B) Blind speed, zero

(C) Delay line cancelling, 2.7 Hz (D) Clutter echoes, 10 Hz

i. The standard LORAN operates in the frequency range of _______ and the low frequency version of LORAN operates at ______.

(A) 1.8 to 2 MHz, 100 K cycles (B) 10 K cycles, 1.75 to 2 MHz

(C) 1.75 to 2 MHz, 10 K cycles (D) 100 K cycles, 1.8 to 2 MHz

j. A target echo is detected 129.30 sec after the radar transmits. How far from the radar is the target in nautical miles.

(A)19.395 km (B) 19.395 n miles

(C)10.47 n miles (D) 10.57 n miles

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Clearly explain radar frequencies and electromagnetic spectrum. (5)

b. Draw a general block diagram of radar and explain the function of each part.

(5)

c. Write a note on applications of radar (6)

Q.3 a. Derive the expression for maximum for maximum radar range that includes bandwidth and receiver noise figure terms. (8)

b. Calculate the maximum range of a radar system which operates at 3 cms with a peak pulse power of 500 KW. If its minimum receivable power is 10^-13 watts, the capture area of its antenna is 5 m² and radar cross sectional area of the target is 20 m². (8)

Q.4 a. With a block diagram explain the operation of an MTI radar. (6)

b. An MTI radar operates at 5 GHz with a pulse repetition frequency of 800 PPS. Calculate the lowest 3 blind speeds of this radar. (6)

c. Write a note on delay line cancellers. (4)

Q.5 a. Derive the frequency response H(f) of a matched filter. (10)

b. With a CW transmit of 5 GHz, calculate the Doppler frequency seen

by a stationary radar when the target radial velocity is 100 km/hr. (6)

Q.6 a. Define clutter. Derive radar range equation for the detection of a target in surface clutter at low grazing angle. (8)

b. Explain how clutter reduction is achieved in radar systems. (4)

c. Explain the Bragg Scatter/resonance with respect to sea echo at long broad wave-lengths. (4)

Q.7 a. Briefly explain the functions of a radar antenna and their parameters. (8)

b. With mathematical steps and with neat diagram explain electronically steered phased array antenna and their chief advantages in radar applications. (8)

Q.8 a. Explain the different types of Duplexer. With block diagram explain their operation and their uses. (6)

b. calculate the minimum receiver signal for a radar receiver which has an IF

band width of 1.5 MHz and a 9 dB noise figures. (5)

c. Explain the performance of a mixer in radar receiver with neat diagram. (5)

Q.9 Write an explanatory notes on the following:

(i) Tracking radar

(ii) Radar Beacons and their applications

(iii) Radio direction finding

(iv) Aircraft landing system. (44)