Integrated Filtering Class-F Power Amplifier Based on Microstrip Multimode Resonator

Filtering power amplifiers (PAs) combine two functions into one circuit and 2-order cascaded structure with two transmission poles (TPs) is the most common form. Multiple TPs can extend bandwidth and minimize in-band ripple. However, more resonators are required for traditional topologies, resulting in large size with high loss. A microstrip filtering Class-F is proposed based on the couple-line multimode impedance transformer (IT) in this paper. Four TPs are created by using only a single resonator. Lengths of the drain bias stub and coupled feed line are carefully chosen to meet the requirement for Class-F operation. The fabricated multimode filtering Class-F PAs is measured at 3.6 GHz for 5G applications. Maximum gain at saturation is 12 dB with output power Pout>38.5 dBm. Maximum power added efficiency (PAE) is 63%, while the effective bandwidth is 400 MHz under the condition of PAEs > 50%.