Radar System Fundamentals Flashcards

What frequency band do most commercial marine navigation radars operate in for short-range coastal navigation?

Answer: X-band (8–12 GHz, typically 9.2–9.5 GHz)

X-band radars operating at approximately 9.3–9.5 GHz are the most common marine navigation radars because their shorter wavelength provides finer resolution and suits smaller antennas.

What is the radar horizon, and what factor primarily determines it for a given installation?

Answer: The geometric line-of-sight distance to the sea surface; primarily determined by antenna height

The radar horizon is approximately 1.22 × √(antenna height in feet) nautical miles; since radar waves travel slightly beyond the geometric horizon due to refraction, antenna height is the dominant factor.

Which parameter directly controls the range resolution of a pulsed radar?

Answer: Pulse width (pulse duration)

Range resolution equals c × τ / 2, where τ is the pulse width; shorter pulses resolve closely spaced targets at the same bearing more precisely.

What is 'rain clutter' and which radar control primarily suppresses it?

Answer: Returns from precipitation; suppressed by the FTC (fast time constant) or differentiation circuit

Rain clutter consists of returns from precipitation filling large areas of the display; the FTC (rain clutter) control differentiates the video signal to enhance target edges and reduce the smeared clutter background.

In a waveguide transmission line used in marine radar, what is the primary advantage over coaxial cable at microwave frequencies?

Answer: Waveguide has lower attenuation and higher power-handling capability at microwave frequencies

At X-band frequencies, coaxial cable has unacceptably high resistive losses; rectangular waveguide carries the signal as a guided wave in air with much lower attenuation and can handle the high peak powers of radar transmitters.

What is the function of the local oscillator (LO) in a superheterodyne radar receiver?

Answer: Produce a frequency slightly offset from the received signal to create an intermediate frequency through mixing

The local oscillator generates a CW signal that the mixer combines with the incoming RF echo to produce the fixed intermediate frequency (typically 60 MHz) at which the bulk of receiver amplification occurs.

What causes 'indirect (false) echoes' on a marine radar display?

Answer: Radar energy reflected from the ship's own structure before reaching a real target, creating a ghost return

Indirect echoes occur when the radar beam strikes part of the vessel's superstructure (masts, funnels) and is deflected to a target, returning along the same indirect path and appearing on the display at an incorrect bearing or range.