ML‐91 NVIS antenna and design the roof rack antenna

I have to design a NVIS roof rack antenna for the following specifications.

Frequency range: 3.3 ‐12.5 GHz.
Power rating: 125 PEP
Receive bandwidth: 45 KHz at 3 GHz and 290 KHz at 12.5 GHz.
Tuning method: Continuously variable tuning capacitor.
Drive Method: Microprocessor controlled precision stepper motor.
Dimensions: Standard rack 1800x1250
Compact rack 1500x1250

anyone has any idea at all??