Hi Farhan;
That's an interesting idea. I'd be concerned that the 1N4148 might be a bit delicate in this application. If it fails (and it will fail shorted like most diodes do) then +12 Volts will be sent to the Gate which is going to blow a fuse.
If you're willing to throw more parts at the idea - Zeners or maybe a simple voltage divider circuit made from resistors could be used to turn on another FET that pulls the drive RF to ground. This idea could be extended to include input from the Power/SWR detector to both act like an ALC, and to fold back the output power when there's a high SWR.
73; Steve, N3SB
