The effect of dispersion on the bandwidth of distributed amplifier

This paper presents a new GaAs P-HEMT distributed amplifier that employs a coplanar waveguide (CPW) as a transmission line taking into account the effect of CPW dispersion on the performance of the amplifier. It is shown that a wide-band amplifier can be designed if the effect of CPW dispersion is kept as minimum as possible. The CPW is first modeled with a pi-section and the parameters (capacitance and inductance) of this model were obtained using its S-parameters with ADS software. From the capacitance and inductance per unit length of CPW line, the length of CPW is calculated to provide required characteristic impedance of artificial transmission line for distributed amplifier. The method of moment (MOM) is used to analysis the dispersion of CPW line. By removing the substrate between the signal and ground metal which makes CPW inductive and less dispersive, a 20% bandwidth enhancement and 17% size reduction were achieved which are of great important for MMIC applications.