Widely Tunable High-Efficiency Power Amplifier With Ultra-Narrow Instantaneous Bandwidth

This paper reports the first power amplifier (PA) that simultaneously achieves a very narrow instantaneous bandwidth (2%) while being tunable over a 38.5% frequency range (2.1-3.1 GHz) with a measured 50%-60% efficiency in the entire band. Such PAs are in great demand for realizing all-digital burst-mode transmitters that are expected to become critical for the future generation of wireless communication systems. Unlike state-of-the-art planar PAs that cannot simultaneously achieve a narrow bandwidth and high efficiency, the presented PA employs a widely tunable high-Q (Q > 300 over the tuning range) cavity resonator as the output matching network. Furthermore, the tunable multiband matching is performed for both the fundamental frequency and the second harmonic to ensure a high efficiency. The measured PA is implemented with a Cree GaN transistor, and it delivers an output power of >= 36 dBm at a gain of >= 10 dB. Two-tone testing is further conducted, indicating a good linearity of this PA with an output third-order intercept point greater than 48 dBm over the entire band. This design demonstrates, for the first time, that multiband burst-mode transmitters can be potentially built with widely tunable high-efficiency narrowband PAs.