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Defence Sensors & Radar

 

Defence Technology Series: 1. What Is Defence Technology? → 2. Sensors & Radar

Defence Sensors & Radar: How Machines “See” the Invisible

Translating electromagnetic pulses into distance, speed, and situational awareness

The goal: detection, distance, velocity

A radar system is one of the most ubiquitous defence sensors. Its job is deceptively simple in description: emit electromagnetic energy, capture reflections, and interpret them into meaningful information about objects in space — their range, direction, and motion. But behind that simple description lies rich physics and sophisticated signal processing that distinguish radar designed for aerospace, missiles, or sea surveillance.

Principles of radar operation

Radar stands for Radio Detection and Ranging. At its core, a radar transmits electromagnetic waves and waits for their echoes. The time between sending a pulse and receiving its reflection gives the distance to a target, based on:

Range = (c × Δt) / 2
where c is the speed of light and Δt is the round-trip echo time.

The division by two exists because the wave must travel to the object and then back. This fundamental equation underpins all pulsed radar systems. 0

Pulse vs continuous wave radar

A radar can emit energy in bursts (pulses) or continuously:

  • Pulsed radar sends short bursts. It easily separates distance information by measuring echo timing. 1
  • Continuous-wave (CW) radar emits a steady signal and detects targets by measuring changes in frequency due to motion — thanks to the Doppler effect. 2

Doppler effect: motion through frequency shifts

When an object moves relative to the radar, the frequency of the reflected signal changes — a principle known as the Doppler effect, first described in classical wave theory. 3

For radar, this means that the frequency received from a moving target will be shifted above the transmitted frequency if the object approaches, and below it if it recedes. This frequency shift is proportional to the object’s radial velocity (toward or away from the radar). 4

Why Doppler matters for defence radars

Modern radar systems — especially those used for air defence or missile tracking — combine pulse timing with Doppler processing. These “pulse-Doppler” radars can measure a target’s range and velocity at once, and they can suppress stationary noise (“clutter”) more effectively than simple pulse systems. 5

Angle and resolution

Beyond range and velocity, a radar must localize targets in direction. It does this with directed antenna beams. A pencil-like beam gives fine angular precision; a fan-shaped beam trades precision for wide coverage. 6

More advanced systems like phased arrays steer beams electronically without moving parts, enabling faster scanning and simultaneous tracking of multiple objects. 7

Signal processing: from echo to insight

Raw echo signals are noisy and complex. Modern defence radars incorporate digital signal processing that amplifies weak returns, filters clutter, and interprets patterns to extract meaningful target characteristics. Techniques such as space-time adaptive processing improve sensitivity even in environments with interference, jamming, or overlapping returns. 8

Types of radar sensors

Radar comes in many flavors, each optimized for specific defence tasks:

  • Surveillance radar – long-range scanning, early detection
  • Tracking radar – follows a specific target’s trajectory
  • Fire-control radar – provides precise targeting data for weapons
  • Missile-borne radar – seeker radars embedded in missiles

Indian radar systems: a glance

India’s DRDO has developed multiple radar systems for air defence and surveillance. Examples include battlefield surveillance radars and 3D airspace radars that detect and track aerial targets in all weather. 9

Emerging directions

Radar research is pushing beyond classical limits. Concepts like quantum-enhanced radar — which uses entangled microwave photons to improve detection in noisy environments — are in early research stages and show how even foundational sensor technology continues to evolve. 10

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