MCQ in Microwave Communications Part 6 | ECE Board Exam

This is the Multiples Choice Questions Part 6 of the Series in Microwave Communications as one of the Communications Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies, Communications Books, Journals and other Communications References.

MCQ Topic Outline included in ECE Board Exam Syllabi

• MCQ in Basic Principles of Microwave Communications
• MCQ in Electro-Optics
• MCQ in Photonics
• MCQ in Optoelectronics
• MCQ in Electromagnetics
• MCQ in Avionics, Aerospace, Navigational and Military Applications
• MCQ in Medical Electronics
• MCQ in Cybernetics
• MCQ in Biometrics

Continue Practice Exam Test Questions Part 6 of the Series

251. Which of the following is not true: The radar cross section of a target

a) depends on the frequency used

b) may be reduced by special coating of the target

c) depends on the aspect of a target, if this non-spherical

d) is equal to the actual cross-sectional area for small targets

252. It is a general term applied to the reduction in signal strength at the input to a receiver

a) fading

b) attenuation

c) absorption

d) ghosting

253. Indicate which of the following cannot be followed by the word “waveguide”

a) elliptical

b) flexible

c) coaxial

d) ridged

254. If the ratio of the antenna diameter to the wavelength in a radar system is high, this will result in (indicate the false statement)

a) large maximum range

b) good target discrimination

c) difficult target acquisition

d) increased capture area

255. High-power TWTs are replacing what in microwave amplifiers?

a) MESFETs

b) Magnetrons

c) Klystrons

d) IMPATT diodes

256. The most widely used microwave antenna is a

a) half-wave dipole

b) quarter-wave probe

c) single loop

d) horn

257. Applies to propagation variables in the physical radio path which affect changes in path loss between the transmitter at one station and its normal receiver at the other station.

a) ghosting

b) absorption

c) attenuation

d) fading

258. If the antenna diameter in a radar system is increased by a factor of 4, the maximum range will be increased by a factor of

a) square root of 2

b) 2

c) 4

d) 8

259. If the peak transmitted power in a radar system is increased by a factor of 15, the maximum range will be increased by a factor of

a) 2

b) 4

c) 8

d) 16

260. Varactor and step-recovery diodes are widely used in what type of circuit?

a) amplifier

b) oscillator

c) frequency multiplier

d) mixer

261. It is defined as line loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects.

a) IRL

b) FSL

c) RSL

d) Eb/No

262. For proper operation, a magnetron must be accompanied by a

a) cavity resonator

b) strong electric field

c) permanent magnet

d) high dc voltage

263. A police radar speed trap functions at a frequency of 1.024 GHz in direct line with your car. The reflected energy from your car is shifted 275 Hz in frequency. Calculate the speed in miles per hour?

a) 60 mph

b) 70 mph

c) 80 mph

d) 90 mph

264. It is the ratio of the wideband carrier to the wideband noise power

a) carrier to noise ratio

b) signal to noise ratio

c) energy per bit per noise density ratio

d) noise figure

265. What is the duty cycle of a radar pulse if the pulse width is 1µs, the pulse repetition rate is 900, and the average power is 18 W?

a) 0.09 %

b) 0.99 %

c) 0.90 %

d) 1.00 %

266. A microwave tube amplifier uses an axial magnetic field and a radial electric field. This is the

a) reflex klystron

b) coaxial magnetron

c) traveling-wave magnetron

d) CFA

267. Figure of merit used to indicate how much the signal-to-noise ratio deteriorates as a signal passes through a circuit or series of circuits

a) noise factor

b) signal to noise ratio

c) carrier to noise ratio

d) dynamic range

268. What is the peak power of a radar pulse if the pulse width is 1µs, the pulse repetition rate is 900, and the average power is 18 W?

a) 10 kW

b) 15 kW

c) 20 kW

d) 30 kW

269. The point where the antenna is mounted with respect to the parabolic reflector is called the

a) focal point

b) center

c) locus

d) tangent

270. The operating frequency of klystron and magnetrons is set by the

a) cavity resonators

b) DC supply voltage

c) input signal frequency

d) Number of cavities

271. Using a small reflector to beam waves to the larger parabolic reflector is known as

a) focal feed

b) horn feed

c) cassegrain feed

d) coax feed

272. If the noise figures and gains of each of the amplifiers in cascade is 3 dB and 10 dB respectively. What is the total noise figure?

a) 2.12 dB

b) 3.24 dB

c) 1.24 dB

d) 4.23 dB

273. One of the following is unlikely to be used as a pulsed device

a) multicavity klystron

b) BWO

c) CFA

d) TWT

274. Calculate the maximum ambiguous range for a radar system with PRT equal to 400µs.

a) 13.8 mi

b) 43.5 mi

c) 16.4 mi

d) 32.8 mi

275. When electromagnetic waves are propagated in a waveguide

a) they travel along the broader walls of the guide

b) they are reflected from the walls but do not travel along them

c) they travel through the dielectric without the walls

d) they travel along all four walls of the waveguide

276. What is the distance in nautical miles to a target if it takes 123 µs for a radar pulse to travel from the radar antenna to the target, back to the antenna, and be displayed on the PPI scope?

a) 10 nmi

b) 5 nmi

c) 20 nmi

d) 15 nmi

277. Waveguides are used mainly for microwave signals because

a) they depend on straight-line propagation which applies to microwaves only

b) losses would be too heavy at lower frequencies

c) there are no generators powerful enough to excite them at lower frequencies

d) they would be too bulky at lower frequencies

278. Calculate the coupling of a directional coupler that has 70 mW into the main guide and 0.35 mW out the secondary guide.

a) 13 dB

b) 23 dB

c) 33 dB

d) 10 dB

279. The wavelength of a wave in a waveguide

a) is greater than in free space

b) depends only on the waveguide dimensions and the free space wavelength

c) is inversely proportional to the phase velocity

d) is directly proportional to the group velocity

280. A rectangular waveguide is 1 cm by 2 cm. Calculate the cutoff frequency

a) 3.5 GHz

b) 15 GHz

c) 7.5 GHz

d) 4 GHz

281. The main difference between the operation of transmission liners and waveguides is that

a) the latter is not distributed, like transmission lines

b) the former can use stubs and quarter-wave transformers, unlike the latter

c) transmission lines use the principal mode of propagation, and therefore do not suffer from low-frequency cut-off

d) terms such as impedance matching and standing-wave ratio cannot be applied to waveguides

282. The useful power of the transmitter that is contained in the radiated pulses is termed as ______.

a) rms power

b) rated power

c) peak power

d) average power

283. In radars, echoes that are produced when the reflected beam is strong enough to make a second trip

a) double range echoes

b) double frequencies echoes

c) second return echoes

d) second time around echoes

284. Indicate the false statement. Compared with equivalent transmission lines, 3 GHz waveguides

a) are less lossy

b) can carry higher powers

c) are less bulky

d) have lower attenuation

285. The range beyond which targets appear as second return echoes is called

a) maximum range

b) maximum unambiguous range

c) maximum usable range

d) any of these

286. When a particular mode is excited in a waveguide, there appears an extra electric component, in the direction of propagation. The resulting mode is

a) transverse electric

b) transverse magnetic

c) longitudinal

d) transverse-electromagnetic

287. In radars, echoes that arrive after the transmission of the next pulse are called _____.

a) second return echoes

b) second time around echoes

c) multiple time around echoes

d) any of these

288. When electromagnetic waves are reflected at an angle from a wall, their wavelength along the wall is

a) the same as the free space

b) the same as the wavelength perpendicular to the wall

c) shortened because of the Doppler effect

d) greater than in the actual direction of propagation

289. A radar mile is equivalent to

a) 2000 mi

b) 2000 m

c) 2000 yd

d) 2000 km

290. As a result of reflections from a plane conducting wall, electromagnetic waves acquire an apparent velocity of light in space

a) velocity of propagation

b) normal velocity

c) group velocity

d) phase velocity

291. In radars, the time between pulses is called ______.

a) rest time

b) duration time

c) delay time

d) propagation time

292. Indicate the false statement. When the free-space wavelength of a signal equals the cutoff wavelength of the guide

a) the group velocity of the signal becomes zero

b) the phase velocity of the signal becomes infinite

c) the characteristic impedance of the guide becomes infinite

d) the wavelength within the waveguide becomes infinite

293. In radars, the duration of the pulse is

a) duty cycle

b) pulse width

c) pulse amplitude

d) pulse cycle

294. A signal propagated in a waveguide has a full wave electric intensity change between two further walls, and no component of the electric field in the direction of propagation. The mode is

a) TE11

b) TE10

c) TM22

d) TE20

295. In radars, the number of the pulses transmitted per second is called

a) pulse repetition frequency

b) pulse repetition time

c) pulse repetition phase

d) pulse number of repetition

296. Which of the following is incorrect? The dominant mode of propagation is preferred with rectangular waveguides because

a) it leads to the smallest waveguide dimensions

b) the resulting impedance can be matched directly to coaxial lines

c) it is easier to excite than other modes

d) propagation of it without any spurious generation can be ensured

297. It is a mean of employing radio waves to detect and locate objects such as aircraft, ships and land masses.

a) detectors

b) radars

c) repeaters

d) beacons

298. A choke flange may be used to couple two waveguides

a) to help the alignment of the waveguides

b) because it is simpler than any other join

c) to compensate for discontinuities at the join

d) to increase the bandwidth of the system

299. The resonant frequency of a cavity may be varied by changing any of these parameters except:

a) cavity volume

b) cavity inductance

c) cavity capacitance

d) cavity resistance

300. In order to couple two generators to a waveguide system without coupling them to each other, which could not be use?

a) rat-race

b) E-plane T

c) hybrid ring

d) magic T

Questions and Answers in Microwave Communications and Principles Series

Following is the list of multiple choice questions in this brand new series:

Complete List of MCQ in Communications Engineering per topic