Antennas, Radar & Navigation

When considering a 3D antenna radiation pattern, the azimuth angle usually covers what range?

A. 0-270

B. 0-180

C. 0-90

D. 0-360

D

When considering a 3D antenna radiation pattern, the elevation angle usually covers what range?

A. 0-180

B. 0-90

C. 0-360

D. 0-270

A

For signal traveling in free space, if the frequency increases, the wavelength:

A. Increases proportionally

B. Remains constant

C. Decreases

D. Becomes zero

C

For a radio, or wireless, communications system radiated power decays with distance (R) as

A. 1/R

B. 1/R^3

C. 1/R^2

D. 1/R^6

C

If a radio communications system has a loss of 300dB at R 10km, what is the loss at R 20km?

A. 606dB

B. 306dB

C. 150dB

D. 600dB

B

What type of antenna would you typically use for a point-to-point communications link?

A. Parabolic dish

B. Monopole

C. Dipole

D. Square loop

A

What type of antenna would you typically use for a radio broadcast link?

A. Helix

B. Aperture antenna

C. Parabolic dish

D. Monopole

D

If largest dimension of an antenna is 1m and the frequency is 2GHz, what is the approximate far-field distance?

A. 23m

B. 13m

C. 3m

D. 6m

B

What is the unit of solid angle?

A. radian

B. elevation

C. steradian

D. m^2

C

What are the units of radiation density?

A. W/m

B. W/m^2

C. W/m^4

D. W^2/m^2

B

What are the units of radiation intensity?

A. W/m^2

B. W/radian

C. W/(solid angle)

D. W^2/(solid angle)^2

C

Antenna gain is normally expressed using what units?

A. dBm

B. dBx

C. dBW

D. dBi

D

If an antenna has a radiation efficiency of n, what is the relationship between the antenna gain (G) and directivity (D)?

A. G=(D/n)^2

B. G=2D/n

C. G=nD

D. G=n/D

C

In a radio communications system what is the product of the input power and the gain called?

A. EIRP

B. PIRE

C. EPIP

D. IRPE

A

An antenna has a gain of 0dB, what is this value in linear?

A. 1

B. 2

C. 3

D. 0.5

A

The polarization of a radio wave is generally defined as

A. the direction of the E field

B. the direction of the H field

C. the direction of the Poynting vector

A

An antenna with perfect circular polarisation has an axial ratio of

A. 0.1

B. 0.5

C. 2

D. 1

D

In the equivalent circuit of an antenna, what does ZA represent?

A. Antenna impedance

B. Antenna resistance

C. Antenna reactance

D. Antenna inductance

A

In the equivalent circuit of an antenna, what does RA represent?

A. Antenna capacitance

B. Antenna resistance

C. Antenna reactance

D. Antenna impedance

B

The correct equation for antenna radiation efficiency is?

A. RR /(ZL+ RR)

B. RL /(RL+ RR)

C. RR /(RL+ RR)

D. ZR /(RL+ RA)

C

What does VSWR stands for?

A. Voltage Single Wave Ratio

B. Voltage Simple Wave Ratio

C. Voltage Standing Wave Ratio

D. Voltage Standing Wave Return

C

A perfect match is indicated by a VSWR of?

A. 0.5

B. -0.5

C. 1

D. -1.0

C

A perfect short circuit is indicated by a reflection coefficient of?

A. 1

B. 0

C. 0.5

D. -1

D

What is the impedance of free space

A. 1270

B. 4770

C. 277

D. 377

D

In a radio communications system what is the path loss when two isotropic antennas are separated by d=2λ?

A. 20 dB

B. 22 dB

C. 30 dB

D. 24 dB

D

A satellite at a distance of 40,000 km from the receiving earth station operates at 11 GHz. What is the free space path loss?

A. 105.3dB

B. 105.3dB

C. 105.3dB

D. 215.3dB

D

In the far-field region, at a distance R, the fields from a dipole antenna vary as?

A. 1/R

B. 1/R^2

C. 1/R^3

D. 1/R^4

A

In the far-field region, at a distance R, the power from a dipole antenna vary as?

A. 1/R

B. 1/R^2

C. 1/R^3

D. 1/R^4

B

The 3D radiation pattern of a dipole antenna is often described as?

A. Banana

B. Doughnut

C. Shortbread

D. Kitkat

B

The directivity of a short dipole is?

A. 0.5

B. 1.0

C. 1.5

D. 2.0

C

The reactive component of the impedance of a dipole becomes zero when the length is what percentage of a wavelength?

A. 48

B. 45

C. 52

D. 54

A

What is the radiation resistance of a monopole?

A. 17.8

B. 33.5

C. 65.8

D. 36.6

D

If the circumference of a small loop antenna is C, the radiation resistance varies as ?

A. C^4

B. C^3

C. C^2

D. C

A

Compared to a single loop antenna, the radiation resistance of a N-turn loop is increased by ?

A. N^0.5

B. N

C. N^4

D. N^2

D

A half-wavelength monopole antenna is a balanced antenna.

A. True

B. False

B

Which of the following is a common type of aperture antenna?

A. Dipole antenna

B. Horn antenna

C. Monopole antenna

D. Loop antenna

B

The far-field radiation pattern of a 2D aperture is mathematically related to which of the following?

A. 1D Laplace transform

B. 2D Fourier transform of the aperture field distribution

C. Convolution of the physical area

D. Taylor series expansion

B

What is the definition of Aperture Efficiency

A. Physical area / Effective area

B. Gain / Beamwidth

C. Effective area / Physical area

D. Main beam power / Sidelobe power

C

What happens to the antenna performance when an "illumination taper" (variation in amplitude across the aperture) is applied?

A. Reduction in gain, reduced sidelobes, and increased beamwidth

B. Increase in gain, reduced sidelobes, and decreased beamwidth

C. Reduction in gain, increased sidelobes, and increased beamwidth

D. No effect on performance

A

In RADAR applications, why are sidelobes generally considered unwanted?

A. They increase the physical size of the antenna

B. They cause the antenna to be more expensive

C. They can give rise to false detection and receive unwanted "clutter" signals

D. They decrease the frequency of operation

C

What is a primary advantage of using an "offset reflector" antenna?

A. It increases the physical area of the dish

B. It reduces feed blockage

C. It allows for lower frequency operation

D. It eliminates the need for a parabolic surface

B

Which type of antenna is specifically noted for its use in "Sky dishes" and rotating radar antennas because it reduces feed blockage?

A. Shaped reflector

B. Multi-beam reflector

C. Offset reflector

D. Standard dipole

C

An active phased array antenna can perform electronic beam steering?

A. True

B. False

A

An active phased array antenna can perform adaptive nulling?

A. True

B. False

A

The mean output power of the Fylingdales radar antenna is approximately?

A. 1.5 MWatts

B. 2.0 MWatts

C. 2.5 MWatts

D. 1.0 MWatts

C

Which of the following equations is correct?

A. ARRAY PATTERN=ELEMENT PATTERN× ELEMENT PATTERN

B. ARRAY PATTERN=ELEMENT PATTERN/ARRAY FACTOR

C. ELEMENT PATTERN=ARRAY PATTERN ×ARRAY FACTOR

D. ARRAY PATTERN=ELEMENT PATTERN×ARRAY FACTOR

D

The Fylindales radar antenna is an example of a passive array antenna?

A. True

B. False

B

Two antennas (one having gain G and the second with gain 3G [both linear units]) are connected by coax cable to form a simple two element array. What is the maximum gain?

A. 5G

B. 3G

C. 2G

D. 4G

D

What is the maximum element spacing (in terms of wavelength) in a linear array to prevent grating lobes?

A. 0.75

B. 1.0

C. 0.25

D. 0.5

D

An antenna has a gain of 3dBi. What is this in linear units?

A. 2

B. 1

C. 3

D. 4

A

Ten antenna elements each with gain of 3dBi are used to form a 10-element array. What is the maximum gain in dBi?

A. 20

B. 10

C. 13

D. 23

C

An 8-element array consists of identical element each with an individual gain of 8 [linear]. What is the maximum gain in dBi?

A. 64

B. 16

C. 32

D. 18

D

RADAR stands for

A. Radio Detection and Ranging

B. Radio Distance and Ranging

C. Radio Detection and Relay

D. Radar Detection and Ranging

A

Which is the most common form of radar

A. Multi-static

B. Passive

C. Bi-static

D. Mono-static

D

In a mono-static radar system the Tx and Rx antennas are co-located?

A. True

B. False

A

In a Bi-static radar system the Tx and Rx antennas are co-located?

A. True

B. False

B

In a mono-static radar system the received power from a target at distance R is proportional to?

A. 1/R^2

B. 1/R^3

C. 1/R^1

D. 1/R^4

D

In a mono-static radar system the power at a target at distance R is proportional to?

A. 1/R^2

B. 1/R^3

C. 1/R

D. 1/R^4

A

The Fylindales radar system is an example of a bi-static radar system?

A. True

B. False

B

A CW Doppler radar system provides information on

A. Target range

B. Target azimuth angle

C. Target speed

D. Target elevation angle

C

A 10GHz mono-static radar detects a target travelling at 100m/s What is the Doppler frequency?

A. 6.67GHz

B. 3.35kHz

C. 6.67kHz

D. 667Hz

C

A 10GHz mono-static radar detects a target with Doppler frequency of 667Hz. What is the target speed?

A. 10 m/s

B. 1 m/s

C. 100 m/s

D. 50 m/s

A

In a pulsed radar system, the return time (τD) of an echo signal from a target at distance R is given by:

A. τD=R/c

B. τD=2R/c

C. τD=3R/c

D. τD=4R/c

B

In a pulsed radar system, if the pulse return time from an echo signal is τD, then the target range R is:

A. R=cτD /4

B. R=cτD /3

C. R=cτD /2

D. R=cτD/1

In a pulsed radar system, what is the relationship between Pulse Repetition Frequency (PRF) and Pulse Repetition Interval (PRI)?

A. PRF* PRI=1

B. PRF=PRI^2

C. PRI=PRF^2

D. 1/PRI=1/PRF

A

A basic pulsed radar provides no information about target speed.

A. True

B. False

A

In a pulsed radar system, if the pulse width is 1µs, then the range resolution is:

A. 300 m

B. 50 m

C. 100 m

D. 150 m

D

In a pulsed radar system, if the pulse width is 1µs, the PRI is 1ms, and the peak transmit power is 100 kW, then the average transmit power is:

A. 100 W

B. 10 W

C. 200 W

D. 20 W

A

In a pulsed radar system, multiple PRFs can be used to avoid range ambiguities.

A. True

B. False

A

In a pulsed Doppler radar system, in-phase (I) and quadrature (Q) channels are used to provide phase information.

A. True

B. False

A

In a pulsed Doppler radar system, for the Doppler shift (Δf) not to be ambiguous, then the following condition applies:

A. Δf ≤ PRF/2

B. Δf ≤ PRF/2

C. Δf ≤ PRF/2

D. Δf ≤ PRF/2

A

In a pulsed Doppler radar system, N pulses are integrated to give a Doppler resolution of:

A. ~2/NT Hz

B. ~1/4NT Hz

C. ~1/NT Hz

D. ~1/2NT Hz

C

In a surveillance radar system, an antenna with a narrow beam gives good angular resolution.

A. True

B. False

A

In a surveillance radar system, an antenna with a narrow beam means fewer scan positions.

A. True

B. False

B

A surveillance radar system uses an antenna with a gain of 36dB. If we need to scan a complete hemisphere of sky, how many beam positions do we need?

A. 1000

B. 500

C. 3000

D. 2000

D

A surveillance radar system uses an antenna with a gain of 39dB. If we need to scan a complete hemisphere of sky, how many beam positions do we need?

A. 1000

B. 2000

C. 4000

D. 500

C

If an antenna rotates at 5rpm, what is the rotation rate in seconds?

A. 6 s

B. 10 s

C. 8 s

D. 12 s

D

Airport surveillance radars normally employ both Primary surveillance radar and SSR?

A. True

B. False

A

What does SSR stand for?

A. secondary single radar

B. secondary surveillance radar

C. sequential scanning radar

D. sequential surveillance radar

B

A pulsed surveillance radar system has a maximum range of 470km. What is the PRF?

A. 319 Hz

B. 401 Hz

C. 367 Hz

D. 263 Hz

A

In a tracking radar system, conical scanning is a mechanical system?

A. True

B. False

A

A monopulse radar system uses two beams to provide sum and difference information for target tracking?

A. True

B. False

A

The rule of balanced observables states that "A stealth object should be designed so that it provides a Low Observable (LO) response to all sensors at a similar range."

A. True

B. False

A

A typical Radar Cross Section (RCS) for a small insect is?

A. 0.001 m^2

B. 1 m^2

C. 0.1 m^2

D. 10 m^2

A

A typical Radar Cross Section (RCS) for a person is?

A. 0.001 m^2

B. 1 m^2

C. 0.1 m^2

D. 10 m^2

B

The RCS versus angle variation for a flat metal plate is approximately a SINC function?

A. True

B. False

A

The RCS versus angle variation for a metal sphere is approximately an elliptical function?

A. True

B. False

B

The maximum RCS of a sphere of radius r is?

A. 2πr^3

B. (4/3)πr^4

C. πr^2

D. 4πr^2

C

A 1kW transmitter that emits its energy in a 10-MHz spectrum provides a power density of 100 watts per MHz. If the same transmitter must spread its energy to cover a spread of 100 MHz, its power density is?

A. 10 W/MHz

B. 1000 W/MHz

C. 20 W/MHz

D. 1 W/MHz

A

A 1kW transmitter that emits its energy in a 10-MHz spectrum provides a power density of 100 watts per MHz. If the same transmitter must spread its energy to cover a spread of 1000 MHz, its power density is?

A. 10 W/MHz

B. 1000 W/MHz

C. 20 W/MHz

D. 1 W/MHz

D

In a radar system, the burnthrough range occurs when the Signal-to-Jam (S/J) ratio is equal to?

A. 0.1

B. 10

C. 2

D. 1

D

In air combat, a stand-forward jammer is often carried on an expendable drone?

A. True

B. False

A