A 3.2–4.2 GHz Wideband 47 dBm GaN HEMT Sequential-LMBA with Harmonic Tuned Using CRLH Transmission Line Stub
This article presents a wideband load modulated balanced amplifier (LMBA) with harmonic tuned using composite right-/left-handed transmission line (CRLH TL) stub. The LMBA is capable of wideband and high-efficiency operation because it does not require a quarter-wavelength (λ/4) line in the output matching circuit, which is an obstacle to wideband operation in Doherty Power Amplifiers (DPAs). To achieve higher efficiency in a smaller size and wider bandwidth, we demonstrate a GaN high electron mobility transistor (HEMT) sequential LMBA (S-LMBA) with a wideband second harmonic matching circuit using a CRLH TL. The proposed harmonic tuning circuit was fabricated to achieve a high reflection coefficient of more than 0.9 for the second harmonic at 3.2-4.2 GHz with a small size of 5.5 mm. The proposed S-LMBA obtained saturation efficiency of 71.6-66.1% and 8 dB BO efficiency of 44.8-41.6% at 3.2-4.2 GHz.