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Semi-Active vs. Passive vs. Active Radar Homing: Key Differences

By RF Wireless Expert Team

This page compares semi-active radar homing, passive radar homing, and active radar homing, highlighting the differences between semi-active, passive, and active radar homing missile systems.

Introduction

Radar homing guidance is a common guidance system for anti-air missiles. Based on their operation, there are three types of radar homing missile systems: semi-active, passive, and active.

Semi-Active Radar Homing

Semi-active Radar Homing

Figure-1 depicts Semi-active Radar Homing working operation.

Here are the features of Semi-active Radar Homing:

  • It uses only a receiver, while the target is illuminated by a nearby radar or another external source.
  • The reflected energy from the target is received by the receiver mounted on the missile.
  • A computer connected to the receiver determines the relative trajectory of the target. This information is used by the missile system to accurately intercept the target.
  • It’s used for long-range air-to-air and ground-to-air missile systems.
  • It’s used for “all-weather” guidance systems as an anti-aircraft system.

Example: 1st generation SAM used by the RSAF

Active Radar Homing

Active Radar Homing

Figure-2 depicts Active Radar Homing working operation.

Here are the features of Active Radar Homing:

  • It transmits energy and receives the reflected energy. Unlike semi-active systems, the missile itself houses both transmitter and receiver components.
  • No external source is needed in this radar homing system.

Examples:

  • AMRAAM air-to-air missile
  • Exocet anti-ship missile

AMRAAM AIM-120 is a combination of both active and semi-active homing. It supports a medium range of about 50 km.

Passive Radar Homing

Passive Radar Homing

Figure-3 depicts Passive Radar Homing working operation.

Here are the features of Passive Radar Homing:

  • It uses heat radiation from the target. The heat energy is used by the missile to determine the target’s parameters.
  • It’s independent of any external guidance system.
  • It only receives the signal and cannot transmit the signal, similar to semi-active radar homing systems.

Examples:

  • Mistral deployed by the RSAF is a passive infrared homing guidance system.
  • AIM9L/M passive IR homing guidance seeker
  • Semi-active and active homing missiles can be detected easily.
  • Passive homing missiles are difficult to detect and easier to break lock on.

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