radar

radar — noun

1. a system that works by sending out high-frequency radio waves and reading their

1.名詞B2
釋義

a system that works by sending out high-frequency radio waves and reading their reflected signals, making it possible to locate far-away things like planes, boats, or approaching storms

例句

Hassan spotted a small plane on his radar screen before anyone else did.

collocation: radar screen

Police set up a radar trap and caught several cars going too fast.

collocation: radar trap

同義詞
  • radio detection and ranging

    the full expanded acronym; highly technical, rarely used in everyday speech

  • sonar

    uses sound waves instead of radio waves; used underwater rather than through air

  • lidar

    uses laser light pulses instead of radio waves; used for high-resolution mapping

文法句型

radar + noun (radar screen, radar system)

adjective + radar (weather radar, police radar)

on radar

用法筆記

Radar is most often uncountable — we say 'the plane appeared on radar' not 'on a radar'. When countable, it refers to a specific type or instance: 'The navy installed three new radars on the base.' The noun is frequently used attributively before another noun (radar screen, radar gun, radar signal).

常見錯誤

❌The air traffic controller looked at a radar.
✅The air traffic controller looked at the radar screen.
💡Radar is typically uncountable; use 'radar screen' or 'radar system' when referring to the display or equipment.
❌The radar showed a storm.
✅The weather radar showed a storm approaching.
💡Adding 'weather' or 'police' before 'radar' specifies the type of system being used.

2. the state of being seen, noticed, or considered by the public or by a particular

2.名詞B2
釋義

the state of being seen, noticed, or considered by the public or by a particular person or group, used mainly in fixed phrases about receiving or avoiding attention — for example, keeping an activity under the radar to avoid detection, or having an issue come onto a decision-maker's radar

例句

That new restaurant is not on my radar yet, but a friend recommended the pasta there.

idiom: not on [possessive] radar

The small startup stayed under the radar for three years before becoming a well-known brand.

idiom: under the radar

同義詞
  • attention

    broader and less colourful; lack the metaphor of detection from a distance

  • awareness

    similar but less vivid; 'public awareness' is more formal than 'on the public radar'

  • notice

    implies a brief or surface-level observation rather than focused attention

反義詞
  • obscurity

    the state of being unknown or unnoticed; more formal and less vivid than the radar metaphor

文法句型

on [possessive] radar

under the radar

off [possessive] radar

come onto [possessive] radar

用法筆記

This is an extended metaphorical sense of the original radar meaning. The phrase 'under the radar' generally has a positive or neutral connotation when describing clever avoidance; 'on someone's radar' can be neutral or slightly urgent. 'Off the radar' is typically neutral, describing something simply not receiving attention. Unlike sense 1, this sense cannot be used with a countable form or in technical compound nouns.

常見錯誤

❌The issue is on radar.
✅The issue is on my radar.' or 'The issue is on the radar of the committee.
💡The metaphorical sense requires a possessive or 'the' before 'radar'; bare 'on radar' is only used in the technical sense.
❌He wants to stay under a radar.
✅He wants to stay under the radar.
💡Always use the definite article 'the' in this fixed phrase.