LAUSR

In this paper, a switchless dual-band, dual-mode power amplifier (PA) has been developed for multioctave operation. For the switchless dual-band operation, we proposed a new coupled-line-based diplexer structure. The proposed diplexer operates as a balun at high-band frequencies and the coupled line at low-band frequencies. To better understand the proposed diplexer structure, a detailed analysis is performed based on a coupled-line theory. The interstage and output-stage matching networks of the PA are designed by using the proposed diplexer. To maximize the power-added efficiency (PAE) of the designed PA, turn off the unused band PAs and decide the optimum off-state bias condition of transistors. The designed dual-band, dual-mode PA is fabricated with commercial 0.25- $\mu \text{m}$ GaN HEMT process. The fabricated PA shows over 15-dB small-signal gain at 5–11 GHz in the low-band mode and 9–18 GHz in the high-band mode. The measured average output power and PAE are 35 dBm, 23% in the low-band mode and 37 dBm, 26% in the high-band mode.