Design of X-band high power amplifier with magnetically coupled transmission line transformer

Abstract

There is an increasing demand for X band radar T/R modules in relation to military and public service use. One of the most important components of the module is a high power amplifier, which should preferably be developed as an MMIC for minimization and reproducibility of the module. For X band compact high power amplifier, the two power combiners are proposed. The high power amplifier with bus-bar combiner is fabricated with HEMT technology. Bus-bar combiner is impedance transforming combiner with simple biasing networks. Improved bus-bar combiner for high output power is proposed. The high power amplifier with tournament-shaped power combiner is proposed and fabricated with HEMT technology. Because the differential structure with tournament-shaped power combiner removes the transmission line for biasing, the size of the power amplifier is decreased. Besides, transmission line transformers of tournament-shaped power combiner are implemented with shorter transmission lines than the transmission lines of bus-bar combiner for impedance transform. Therefore, the tournament-shaped power combiner makes the power amplifier more compact. The amplifier with tournament-shaped combiner has higher power density than that with bus-bar combiner at same output power because of small chip-size. Lastly, the efficiency and linearity characteristics of the parallel matching power combiner and tournament power combiner are discussed in detail. The more combined transistors with tournament power combiner show the better efficient characteristics than the transistors with parallel matching power combiner. Moreover the bias network of the tournament power combiner has more linear characteristics than the bias network of parallel matching combiner. These are proven through the simulation and measurement results. When high power amplifier module for base station is designed, the tournament power combiner can use less surface-mounted device (SMD) capacitors for matching than pa...