Non-linear PHEMT model and it implementation in high gain monolithic X-band amplifier for space communications systems

This paper describes the design of high gain amplifiers for space communications systems in the frequency range of 8-12 GHz using a PHEMT operated at the bias point where the maximum value of transconductance (Gm) occurs. The amplifiers design is based on the knowledge of the small signals equivalent circuit of a PHEMT F4×25 featured by a 0.25μm gate length. The amplifiers design processes involve synthesis of matching networks with Chebyshev response in passive and distribute elements using MDS and Libra programs. A negative feedback is used to achieve the stability condition and flat response of the gain amplifier. In order to predict I_MD (intermodulation distortion), we use the “chen´s” Non - Linear model modeling the drain current Ids(Vgs, Vds) and the first three associates derivaties. Finally, the performance of the amplifier was evaluating using “MDS” commercial simulation software. The achieved gain is 11.5 dB with an input and output VSWR of 1.9 in all the bandwidth.