Radar

Definition

Radar (Radio Detection and Ranging) is a ground-based system used to detect, locate, and track aircraft by transmitting radio waves and analyzing their reflections. In air traffic control (ATC), radar enables real-time monitoring of aircraft position and movement, forming the backbone of surveillance and separation services.

Types of Radar

Type	Name	Function
Primary Radar (PSR)	Passive detection	Measures position using reflected signals; detects any object (aircraft, terrain, birds)
Secondary Surveillance Radar (SSR)	Cooperative	Interrogates onboard transponders to receive aircraft ID, altitude, and other data
Monopulse Secondary Radar	High precision	Advanced SSR for Mode S tracking with higher accuracy

Primary Radar (PSR)

Does not rely on aircraft systems
Detects any object reflecting the radar beam
Provides azimuth (bearing) and distance, but no altitude or identity
Used for military, backup, or non-cooperative target detection
Susceptible to clutter (e.g., weather, terrain)

Secondary Radar (SSR)

Requires aircraft to carry a transponder
Provides aircraft identity (squawk) and pressure altitude (Mode C)
With Mode S, also transmits heading, groundspeed, and callsign
Allows target labeling on controller screens, improving clarity and response

Phraseology Examples

“Radar contact” → ATC has identified your aircraft on radar
“Resume own navigation” → Radar vectors are no longer provided
“Radar service terminated” → Aircraft leaving radar coverage or switching to procedural control

Radar Vectoring

ATC can issue headings to aircraft for sequencing, separation, or traffic avoidance.

Typical instructions include:

“Turn left heading 210”
“Fly heading 060 for spacing”

Radar vectoring is common in approach and departure phases, especially in busy terminal areas.

Radar Identification Methods

Squawk Ident → Controller instructs pilot to press IDENT button
Position correlation → Controller matches position report with radar return
SSR Code Assignment → ATC assigns a discrete squawk code, linked to flight plan
Departure correlation → Known time and runway departure allows positive ID

Limitations of Radar

Line of sight only: Radar coverage depends on aircraft altitude and terrain
Not all airspace is radar-covered: Especially in mountainous or remote areas
Radar separation minima must be maintained (e.g., 3–5 NM horizontally, 1,000 ft vertically)

Radar Services Provided

Traffic sequencing and spacing
Vectoring for approaches
Weather avoidance guidance
Conflict resolution advisories
Transition between airspace sectors

Modern Developments

Mode S radar networks support enhanced surveillance
ADS-B and multilateration are augmenting or replacing radar in some FIRs
Radar screen automation provides data tags showing callsign, level, speed, and intent