Defence Technology Series: 1. What Is Defence Technology → 2. Sensors & Radar → 3. Radar Range Equation → 4. Phased Array & AESA Radars
Phased Array & AESA Radars: Steering Beams Without Moving Metal
How interference, timing, and computation replaced mechanical rotation
The limitation of rotating radars
Classical radar systems rely on mechanically rotating antennas to scan the sky. While robust, this approach has a hard physical limitation: speed. Mechanical systems cannot instantaneously change direction, nor can they easily track many targets at once.
Modern defence environments demand faster reaction times, multi-target tracking, and resistance to jamming. These requirements forced radar engineering to abandon moving metal and embrace wave interference.
The core idea: controlled interference
A phased array radar replaces one large antenna with hundreds or thousands of smaller radiating elements arranged in a grid.
Each element emits electromagnetic waves with the same frequency but with a precisely controlled phase difference.
Where waves add constructively, a strong beam forms. Where they cancel, radiation is suppressed. By adjusting phase delays electronically, the radar steers its beam without physically moving anything.
Beam steering through phase control
Consider two adjacent antenna elements separated by distance d. If the phase difference between them is Δφ, the direction of maximum radiation θ satisfies:
d sinθ = (λ / 2π) Δφ
This relation shows that steering angle is governed purely by wavelength and phase. Change the phase delays, and the beam jumps to a new direction at nearly the speed of light.
From phased array to AESA
Traditional phased array radars often use a single high-power transmitter feeding all elements. AESA — Active Electronically Scanned Array — goes further.
In an AESA radar, each antenna element has its own transmit/receive module. This allows:
- Multiple beams at the same time
- Rapid frequency hopping
- Graceful degradation if some modules fail
- Lower probability of interception
Software-defined radar behavior
In AESA systems, beam patterns, scan strategies, and even radar modes are largely software-controlled.
The same hardware can perform surveillance, tracking, fire control, and electronic counter-countermeasures by altering signal processing algorithms.
Modern radars are closer to high-speed computers with antennas attached than to traditional radio transmitters.
Resolution and array size
Angular resolution in phased array radars depends on the effective aperture size. Larger arrays produce narrower beams.
Beamwidth ≈ λ / D
Here, D is the array dimension. This equation explains why fighter aircraft nose size limits radar performance and why large ground-based radars achieve exceptional angular precision.
Resistance to jamming
AESA radars are naturally resilient to electronic attack. They can change frequency, waveform, and beam direction faster than most jammers can respond.
This agility makes it difficult for adversaries to lock onto or blind the radar without revealing themselves.
Indian context
India has developed indigenous AESA radar systems for airborne and ground-based applications. These systems mark a transition from mechanically scanned radars to software-driven sensing architectures.
Strategic implication
Phased array and AESA radars fundamentally alter the balance between detection and evasion. They compress reaction times and enable layered defence architectures that rely on sensor fusion rather than single sensors.
In modern defence, speed of information is often more decisive than speed of weapons.
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