Designing an oscillator with 270 VDC input

I want to design an oscillator with high voltage of DC input. to be precise I am giving input of 270 Vdc. I want to generate a frequency of 3GHz and above. With the use of crystal oscillator, is it possible to do so or is there any other option for that.

Yeah it is possible, there have been studies about this already. However, because of the high input voltage you want to implement, I think your device will definitely heat up. It is another aspect of your design you'd need to look into considering device sustainability.

You are talking about a microwave RF oscillator and power amplifier, or a CW microwave generator.

At these frequencies, the load you are driving is critical to the design. If you want to generate an RF signal as a radiated EM field at a single frequency, a cavity magnetron would be the easiest way to go at high power levels.

If you want to drive a high impedance load at low power, a crystal oscillator driving a DDS frequency synthesizer driving a power stage will work. A power stage that operates at 3GHz and 270V will be a little tricky as most of the off-the-shelf stuff will be for a 50 ohm (or so) load and will be set up for high power outputs at 270V. You would use a voltage regulator to reduce the 270V to 5 or 3.3v (typically) to run the actual oscillator and only the power stage would run at 270V.