CMRT Radar System Fundamentals 2 — Questions and Answers
Question 1: What is the primary purpose of the radar duplexer in a marine radar system?
- Amplify the transmitted signal before it reaches the antenna
- Switch the antenna between transmit and receive modes to protect the receiver (Correct answer)
- Convert analog radar returns to digital signals
- Regulate the pulse repetition frequency
Correct answer: Switch the antenna between transmit and receive modes to protect the receiver
The duplexer acts as a transmit/receive switch, connecting the antenna to the transmitter during transmission and to the receiver immediately after, protecting the sensitive receiver from the high-power transmit pulse.
Question 2: In radar terminology, what does 'range resolution' refer to?
- The maximum detection distance of the radar
- The ability to distinguish between two targets at the same bearing but different ranges (Correct answer)
- The minimum detectable signal level at the receiver
- The angular separation needed to distinguish two targets side by side
Correct answer: The ability to distinguish between two targets at the same bearing but different ranges
Range resolution is the radar's ability to display two separate targets at the same bearing as distinct returns rather than merging them into one; it is primarily determined by pulse width.
Question 3: Which component in a magnetron-based radar generates the high-frequency microwave energy?
- Klystron tube
- Magnetron oscillator (Correct answer)
- Traveling wave tube
- Gunn diode
Correct answer: Magnetron oscillator
The magnetron is a crossed-field vacuum tube oscillator that converts DC power into microwave energy at the radar's operating frequency, typically in the X-band (9–10 GHz) for marine radars.
Question 4: What effect does increasing the pulse repetition frequency (PRF) have on maximum unambiguous range?
- Increases maximum range because more pulses are transmitted
- Decreases maximum range because the listening period between pulses shortens (Correct answer)
- Has no effect on maximum range
- Doubles maximum range when PRF is doubled
Correct answer: Decreases maximum range because the listening period between pulses shortens
Higher PRF means shorter intervals between pulses, so echoes from distant targets may return after the next pulse is sent, causing range ambiguity and effectively reducing unambiguous range.
Question 5: What is the function of the radar's intermediate frequency (IF) amplifier stage?
- Amplify the transmitted pulse to the required power level
- Amplify the mixed-down received signal before detection (Correct answer)
- Generate the local oscillator frequency
- Convert the video signal to a display format
Correct answer: Amplify the mixed-down received signal before detection
The IF amplifier provides most of the receiver's gain and selectivity by amplifying the signal after it has been down-converted from microwave frequency to a fixed intermediate frequency.
Question 6: Which type of radar scan pattern is standard for surface-search marine navigation radars?
- Sector scan covering only the forward 120°
- Continuous 360° plan position indicator (PPI) scan (Correct answer)
- Raster scan identical to a television display
- Spiral scan starting from the center outward
Correct answer: Continuous 360° plan position indicator (PPI) scan
Marine navigation radars use a continuously rotating antenna producing a 360° PPI display, giving the navigator a complete picture of all surrounding targets.
Question 7: What is 'sea clutter' on a marine radar display?
- Interference caused by other ships' radars operating on the same frequency
- Unwanted returns from waves and wave crests near the vessel (Correct answer)
- Electronic noise generated inside the receiver's amplifier stages
- Rain and precipitation returns masking target echoes
Correct answer: Unwanted returns from waves and wave crests near the vessel
Sea clutter (sea return) is radar energy reflected back from the rough sea surface close to the vessel, appearing as a bright, noisy area around the center of the PPI display.
CMRT Radar System Fundamentals 2
What is the primary purpose of the radar duplexer in a marine radar system?