Radar System Fundamentals Flashcards

What is the significance of the 'blind zone' (dead zone) directly around a radar antenna?

Answer: It is the minimum range within which targets cannot be detected because the duplexer is still recovering

The minimum range or blind zone exists because the duplexer recovery time after transmission prevents the receiver from processing any echoes returned from very close targets.

How does antenna beamwidth affect the azimuthal (bearing) accuracy of a marine radar?

Answer: Narrower beamwidth provides better bearing discrimination and accuracy

A narrower horizontal beamwidth means the antenna illuminates a smaller angular slice of the scene, allowing closer targets at different bearings to be resolved and improving bearing accuracy.

What does the term 'noise figure' describe in a radar receiver?

Answer: The ratio of output noise power to the noise that would exist if the receiver were perfect

Noise figure quantifies how much additional noise a receiver introduces compared to an ideal noiseless receiver, directly affecting the minimum detectable signal and thus detection range.

In a solid-state radar, what replaces the magnetron as the transmit source?

Answer: A solid-state power amplifier (SSPA) using transistors such as GaN devices

Modern solid-state marine radars use gallium nitride (GaN) or similar semiconductor power amplifiers instead of magnetrons, offering longer life, lower peak power with pulse compression, and no high-voltage supplies.

What is 'pulse compression' and why is it used in some marine radars?

Answer: Transmitting a long coded pulse and processing it to achieve the resolution of a short pulse

Pulse compression allows a radar to transmit a long, frequency- or phase-modulated pulse to achieve high average power, then correlate the return to produce the equivalent resolution of a very short pulse.

What is the purpose of the sensitivity time control (STC) circuit in a marine radar receiver?

Answer: Reduce receiver gain at short ranges to suppress sea clutter

STC progressively increases receiver gain with time (range) after each pulse, reducing sensitivity at close ranges where sea clutter is strongest and restoring full sensitivity at longer ranges.

What does ARPA stand for in the context of marine radar systems?

Answer: Automatic Radar Plotting Aid

ARPA (Automatic Radar Plotting Aid) is a system that automatically tracks multiple radar targets, computing their course, speed, closest point of approach (CPA), and time to CPA to assist collision avoidance.