Single and Dual Input Packaged 5.5-6.5GHz, 20W, Quasi-MMIC GaN-HEMT Doherty Power Amplifier

This paper presents the design, the realization and the power characteristics of plastic low cost packaged symmetric Doherty Power Amplifiers (DPA) operating in the 5.5-6.5GHz bandwidth. A single input (SI-DPA) and a dual input (DI-DPA) DPAs are proposed based on two power bars composed of two GaN HEMT cells (8 fingers of 275 mu m unit gate width). Input and output matching networks are designed on passive GaAs MMIC technology. To our knowledge, it is the first published SI and DI-DPAs working in C band, designed using Quasi-MMIC technology and assembled in plastic package. The measured power results under Continuous Wave (CW) signal of the SI-DPA demonstrate a maximum output power (POUT) upper than 20W (43.5dBm) with 50% drain efficiency (DE), 42% power added efficiency (PAE), 11dB of insertion gain (GI) in the 5.5-6.5GHz bandwidth. At 6dB Output power Back-Off (OBO), the drain efficiency is greater than 35% (32% PAE). The DPA linearity has been investigated with a 256QAM modulation signal of 30MHz bandwidth and using Digital Pre-Distortion (DPD) leading to a 50dBc Adjacent Channel Leakage Ratio (ACLR) at a 34 dBm average output power. The designed DI-DPA is identical to the SI-DPA without input power splitter. It demonstrates that the adjustment of power ratio between the main and the peak amplifiers associated with adequate bias points, improves all the power performances: linearity, PAE, OBO and GI. The DI-DPA reaches a 12.5 dB GI, a maximum P-OUT equal to 44dBm (3.5dB gain compression) with 45% PAE. Moreover, in the same previous bandwidth, 40% PAE with 4 degrees of AM/PM variation are obtained at 6dB(OBO) and 36% PAE (AM/PM= 3 degrees) at 8dB(OBO).