High-efficiency and flat-gain Doherty type transmitter using a 180-degree hybrid-combiner

It is well-known that the isolation provided by a hybrid combiner defeats the active load-modulation mechanism between the carrier and peaking power amplifiers in a Doherty transmitter. In this paper, a hybrid combiner is used in combination with a lattice network to combine the carrier and peaking amplifiers in order to manage load modulation between them. Both amplifiers have a driver stage. The driver of the peaking amplifier is tuned and biased so that the efficiency at 6-dB backoff power is peaked. The prototype exhibits an efficiency at peak power of 80.5% and an efficiency at 6-dB back-off of 70.5%. Alternatively, the transmitter can be optimized for flat AM-AM characteristics scarifying efficiency enhancement at back-off power.