PSU's like DRDO always needs Physicists as well as Engineering Physics graduates for there R&D purposes. With a good gate score you can apply for the DRDO or get a shortlisted call from there side (if you have extremely good results). The DRDO interviews are of 4-5 panelists. Each of the panelist are the best of the Defence Scientist in India.

Frequently asked portions in the Interview are:

• Mathematical Physics
• Resolution of fields and forces
• Physical safety measures and safety predictions
• Mechanical Engineering portions like Propulsion, Force Balances etc

To know more about DRDO visit the link below:

https://engineering.careers360.com/articles/drdo-recruitment-through-gate

I hope my answer helps. All the very best for your future endeavors!