Defence electronics is the electronics inside missiles, radars and satellites, built under strict controls on who may see a weapon's designs. The buyers are governments and armed forces. They usually buy through government tenders, in which companies bid and fixed rules choose the winner. In India, the government also asks that more of this equipment be made in India, so Indian companies design and build a growing share of it.
Defence electronics are different from the electronics in an airliner in two ways. The first is secrecy. Countries restrict who may see a weapon's designs. A foreign company often cannot send the design files of a radar to its engineers abroad. So defence engineering is harder to move to another country than commercial work. The second is long life. A radar or a missile system stays in service for decades, and the maker supports it all that time.
Say a company in Ghaziabad designs the receiver board for a radar. Its engineers work on files that are marked as controlled. Only named engineers may open them. Suppliers who help with the board, such as a company that makes the circuit boards, log in through a system that records each session and limits what the supplier can open. That system is vendor privileged access management. This guards against a supply chain attack, in which an attacker enters through a supplier.
The electronics go into many products. They are used in counter-drone systems, which detect hostile drones and stop them, and in mesh and tactical radios, which pass messages from one radio to another without a tower. They are also built into earth observation satellites. Soldiers and pilots practise with them on simulators and instrumented ranges. Sensors such as thermal imaging cameras are part of the same family.
The electronics must also work in harsh conditions: heat in a desert, cold at high altitude, shock and vibration in a vehicle. So they are tested far more than ordinary electronics before they are accepted.