**Abstract**

The small signal characteristics of DDR IMPATTs based on GaAs designed to operate at mm-wave window frequencies such as 94, 140, and 220GHz are presented in this chapter. Both the DC and Small signal performance of the abovementioned devices are investigated by using a small signal simulation technique developed by the authors. The efficiency, output power and power density of GaAs IMPATT is higher than that of Si IMPATT. Results show that the DDR IMPATTs based on GaAs are most suitable for generation of RF power with maximum conversion efficiency up to 220GHz. The noise behavior of GaAs IMPATT yield less noise as compared to Si IMPATT.

**Keywords:** GaAs, IMPATT diode, ionization rates, efficiency, noise
