I. Introduction
The development of systems and application such as high speed communications, spectroscopy and remote sensing extend the need for higher frequency and bandwidth devices and circuits. Due to their high cut off frequency and high maximum oscillator frequency InP HBT devices have been wildly used in various technologies. An accurate and stable small signal equivalent circuit model plays an important role in millimeter-wave circuits designing. Because the model parameters are extracted from the measured S-parameters it is becoming essential to obtain accurate high frequency scattering parameters.