UPSC Prelims 2026 Q47: Drone Swarms — Communication & Countermeasures
Which of the following statements with regard to drone swarms is/are correct?
1. They use Terahertz band of frequency to communicate with the command centre.
2. Individual drones in the swarm can communicate with other drones in the swarm.
3. GPS Spoofing is a commonly used technique to counter drone swarm attack.
- 1 only
- 2 and 3 only
- 1 and 2 only
- 1, 2 and 3
Answer: (b) 2 and 3 only
Statement-wise explanation
- 1: incorrect — Drones, including those in swarms, talk to ground control over ordinary radio-frequency links. These are mostly in the gigahertz range, such as the 2.4 GHz and 5.8 GHz bands, with UHF and satellite links used for longer range. The terahertz band (about 0.1–10 THz) is absorbed heavily by water vapour in the air, so it carries signals only over very short distances. It is still being researched for future 6G systems and is not the standard command-centre link.
- 2: correct — Drone-to-drone communication is what makes a group of drones a swarm. The drones form a peer-to-peer (mesh or ad hoc) network to share position, task and sensor data. This lets them coordinate, avoid collisions and keep working if one drone or the ground link is lost.
- 3: correct — GNSS/GPS spoofing is a standard non-kinetic, 'soft-kill' counter-drone technique. The defender broadcasts fake satellite signals that give the drone false position, velocity and timing data, so it can be pushed off course, forced to land or made to crash. It is used together with RF jamming of control links and with 'hard-kill' options such as guns, missiles and lasers.
How to eliminate
Statement 2 is close to the definition of a swarm. Coordinated flight is not possible unless drones share data with each other, so it is almost certainly true. That removes the option '1 only'. Next, check Statement 1. Terahertz is linked in the news with 6G research, not with drones already in service. Its short range in air makes it a poor choice for a long command link. If you reject Statement 1, the only remaining option is '2 and 3 only'. Statement 3 can also be judged from basic logic: drones depend on satellite navigation, so feeding them false GPS signals is an obvious countermeasure. Facts to remember: drone control links run on GHz-band RF, and counter-drone 'soft kill' means jamming plus spoofing.
Know more
Drone swarms are groups of drones that coordinate on their own to carry out one mission. They use onboard autonomy (often AI) and share data constantly, so the swarm keeps working even if some drones are lost.
How a swarm communicates
- Drone-to-ground link: command and control plus video/telemetry, mostly on RF bands such as 2.4 GHz and 5.8 GHz (and UHF or satellite links for longer range).
- Drone-to-drone link: a mesh/ad hoc network in which each drone can send, receive and relay messages. No single node is critical.
- Navigation: GNSS (GPS, NavIC, etc.) plus onboard inertial sensors.
Terahertz band: 0.1–10 THz, between microwaves and infrared. It offers very high bandwidth, but water vapour absorbs it strongly, so its range is short. It is a candidate for 6G, not a standard drone link.
Counter-drone (C-UAS) toolkit
| Method | Type | How it works |
|---|---|---|
| RF jamming | Soft kill | Floods the control/video link with noise |
| GNSS spoofing | Soft kill | Sends fake satellite signals to mislead navigation |
| Protocol takeover | Soft kill | Hijacks the drone's own control link |
| Guns, missiles, interceptor drones | Hard kill | Physically destroys the drone |
| Directed-energy weapons (laser, microwave) | Hard kill | Burns or fries the airframe or electronics |
Swarms are hard to counter because they are numerous and cheap. Defences therefore favour area-effect soft kill (jamming, spoofing) and low cost-per-shot hard kill such as lasers. DRDO's counter-drone system, transferred to BEL, combines radar, EO/IR and RF detection with jamming and laser-based hard kill.
In the news
Drone swarms and counter-drone defence were widely reported in 2025. During the May 2025 India–Pakistan hostilities (Operation Sindoor), Indian air defences took down swarms of Pakistani drones. Later in 2025 the Indian Army held drone and counter-drone exercises such as Vayu Samanvay-II, and the government pushed for indigenous drone and counter-drone manufacturing.
NCERT Concepts to Revise
- Electromagnetic spectrum: Statement 1 turns on where the terahertz band sits on the spectrum compared with the gigahertz radio bands that drones usually use to reach ground control.
- Electromagnetic radiation: Statements 1 and 3 depend on how radio and satellite signals travel, get absorbed by water vapour, and can be jammed or faked by a defender.