Design of an S-band power combiner system with two parallel power amplifiers and phase shifters

Abstract

RF power amplifiers are important blocks in a wireless communication system that play a vital role in determining the level of overall performance. In some situations, more power than a single power amplifier can alone provide is required in applications such as a radar or a space communication system. In such cases, power combiners that can surpass the maximum output power level of a single power amplifier should be used. In this thesis, we study the performance of a power combiner built in classical binary structure. The combiner operates at 3 GHz (S-band) and comprises two power amplifiers which can supply up to 38 dBm of saturated power. Wilkinson power dividers/combiners are utilized at the input/output respectively in order to divide and combine the input and output signals. While building a power combiner, one should also note that the phases of the amplified signals should be matched at the output or else the level of combining loss can reach significant levels. At a phase difference of 180◦ , the signals will be completely out of phase and will combine destructively at the output. Therefore, in our study, in order to be able to control the phases at each arm of the power combiner, two tunable microwave phase shifters are placed before the active devices. The phase shift generated by these shifters are controlled via voltage, hence a desired level of phase shift can be obtained. By this, we demonstrate that phase shifters are also important structures for a power combiner that are instrumental in accomplishing a phase balance between the two arms. The idea behind the work displayed here can be extended to applications requiring much higher power levels or operating at higher frequencies.